Chin. Phys. B

Soliton molecules and asymmetric solitons of the extended Lax equation via velocity resonance

Hongcai Ma(马红彩), Yuxin Wang(王玉鑫), and Aiping Deng(邓爱平)

Chin. Phys. B, 2022, 31 (1): 010201. DOI: 10.1088/1674-1056/ac0907

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We investigate the techniques for velocity resonance and apply them to construct soliton molecules using two solitons of the extended Lax equation. What is more, each soliton molecule can be transformed into an asymmetric soliton by changing the parameter φ. In addition, the collision between soliton molecules (or asymmetric soliton) and several soliton solutions is observed. Finally, some related pictures are presented.

Theoretical study of (e, 2e) triple differential cross sections of pyrimidine and tetrahydrofurfuryl alcohol molecules using multi-center distorted-wave method Suggested by editors

Yiao Wang(王亦傲), Zhenpeng Wang(王振鹏), Maomao Gong(宫毛毛), Chunkai Xu(徐春凯), and Xiangjun Chen(陈向军)

Chin. Phys. B, 2022, 31 (1): 010202. DOI: 10.1088/1674-1056/ac21c3

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We report theoretical studies of electron impact triple differential cross sections of two bio-molecules, pyrimidine and tetrahydrofurfuryl alcohol, in the coplanar asymmetric kinematic conditions with the impact energy of 250 eV and ejected electron energy of 20 eV at three scattering angles of -5 °, -10 °, and -15 °. Present multi-center distorted-wave method well describes the experimental data, which was obtained by performing (e, 2e) experiment. The calculations show that the secondary electron produced by the primary impact electron is strongly influenced by the molecular ionic multi-center potential, which must be considered when the low energy electron interacts with DNA analogues.

Protection of entanglement between two V-atoms in a multi-cavity coupling system

Wen-Jin Huang(黄文进), Mao-Fa Fang(方卯发), and Xiong Xu(许雄)

Chin. Phys. B, 2022, 31 (1): 010301. DOI: 10.1088/1674-1056/ac0bb2

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The protection of the entanglement between two V-atoms (EBTVA) in a multi-cavity coupling system is studied. The whole system consists of two V-atoms. The two V-atoms are initially in the maximum entangled state and interacts locally with its own dissipative cavity which is coupled to the external cavities with high quality factor (ECWHQF). The results show that, when there is no ECWHQF, the EBTVA can be protected effectively in the case where the V-atom and the dissipative cavity are weak coupled in large detuning, while when there are different numbers n of ECWHQF coupled to two dissipative cavities, by adjusting the parameters of the number n of ECWHQF and the coupling strength k between cavities, the EBTVA can be protected perfectly and continuously. Our result provides an effective method for protecting entanglement resources of three-level system.

Semi-quantum private comparison protocol of size relation with d-dimensional GHZ states

Bing Wang(王冰), San-Qiu Liu(刘三秋), and Li-Hua Gong(龚黎华)

Chin. Phys. B, 2022, 31 (1): 010302. DOI: 10.1088/1674-1056/ac1413

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A novel efficient semi-quantum private comparison protocol based on the d-dimensional GHZ states is proposed. With the assistance of semi-honest third party, two classical participants can compare the size relation of their secrets without any information leakage. To reduce the consumption of quantum devices, the qubit efficiency of our protocol is improved by introducing the semi-quantum conception via the existing semi-quantum private comparisons. Furthermore, it is unnecessary to prepare the secure classical authentication channel among participants in advance. It is shown that our protocol is not only correct and efficient, but also free from external and internal attacks.

Determination of quantum toric error correction code threshold using convolutional neural network decoders

Hao-Wen Wang(王浩文), Yun-Jia Xue(薛韵佳), Yu-Lin Ma(马玉林), Nan Hua(华南), and Hong-Yang Ma(马鸿洋)

Chin. Phys. B, 2022, 31 (1): 010303. DOI: 10.1088/1674-1056/ac11e3

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Quantum error correction technology is an important solution to solve the noise interference generated during the operation of quantum computers. In order to find the best syndrome of the stabilizer code in quantum error correction, we need to find a fast and close to the optimal threshold decoder. In this work, we build a convolutional neural network (CNN) decoder to correct errors in the toric code based on the system research of machine learning. We analyze and optimize various conditions that affect CNN, and use the RestNet network architecture to reduce the running time. It is shortened by 30%-40%, and we finally design an optimized algorithm for CNN decoder. In this way, the threshold accuracy of the neural network decoder is made to reach 10.8%, which is closer to the optimal threshold of about 11%. The previous threshold of 8.9%-10.3% has been slightly improved, and there is no need to verify the basic noise.

Low-loss belief propagation decoder with Tanner graph in quantum error-correction codes

Dan-Dan Yan(颜丹丹), Xing-Kui Fan(范兴奎), Zhen-Yu Chen(陈祯羽), and Hong-Yang Ma(马鸿洋)

Chin. Phys. B, 2022, 31 (1): 010304. DOI: 10.1088/1674-1056/ac11cf

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Quantum error-correction codes are immeasurable resources for quantum computing and quantum communication. However, the existing decoders are generally incapable of checking node duplication of belief propagation (BP) on quantum low-density parity check (QLDPC) codes. Based on the probability theory in the machine learning, mathematical statistics and topological structure, a GF(4) (the Galois field is abbreviated as GF) augmented model BP decoder with Tanner graph is designed. The problem of repeated check nodes can be solved by this decoder. In simulation, when the random perturbation strength p=0.0115-0.0116 and number of attempts N=60-70, the highest decoding efficiency of the augmented model BP decoder is obtained, and the low-loss frame error rate (FER) decreases to 7.1975×10^-5. Hence, we design a novel augmented model decoder to compare the relationship between GF(2) and GF(4) for quantum code [[450,200]] on the depolarization channel. It can be verified that the proposed decoder provides the widely application range, and the decoding performance is better in QLDPC codes.

Quantum multicast communication over the butterfly network Suggested by editors

Xing-Bo Pan(潘兴博), Xiu-Bo Chen(陈秀波), Gang Xu(徐刚), Zhao Dou(窦钊), Zong-Peng Li(李宗鹏), and Yi-Xian Yang(杨义先)

Chin. Phys. B, 2022, 31 (1): 010305. DOI: 10.1088/1674-1056/ac20c6

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We propose a scheme where one can exploit auxiliary resources to achieve quantum multicast communication with network coding over the butterfly network. In this paper, we propose the quantum 2-pair multicast communication scheme, and extend it to k-pair multicast communication over the extended butterfly network. Firstly, an EPR pair is shared between each adjacent node on the butterfly network, and make use of local operation and classical communication to generate entangled relationship between non-adjacent nodes. Secondly, each sender adds auxiliary particles according to the multicast number k, in which the CNOT operations are applied to form the multi-particle entangled state. Finally, combined with network coding and free classical communication, quantum multicast communication based on quantum measurements is completed over the extended butterfly network. Not only the bottleneck problem is solved, but also quantum multicast communication can be completed in our scheme. At the same time, regardless of multicast number k, the maximum capacity of classical channel is 2 bits, and quantum channel is used only once.

Vacuum-gap-based lumped element Josephson parametric amplifier

Sishi Wu(吴思诗), Dengke Zhang(张登科), Rui Wang(王锐), Yulong Liu(刘玉龙), Shuai-Peng Wang(王帅鹏), Qichun Liu(刘其春), J S Tsai(蔡兆申), and Tiefu Li(李铁夫)

Chin. Phys. B, 2022, 31 (1): 010306. DOI: 10.1088/1674-1056/ac280c

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We propose a lumped element Josephson parametric amplifier with vacuum-gap-based capacitor. The capacitor is made of quasi-floating aluminum pad and on-chip ground. We take a fabrication process compatible with air-bridge technology, which makes our design adaptable for future on-chip integrated quantum computing system. Further engineering the input impedance, we obtain a gain above 20 dB over 162-MHz bandwidth, along with a quasi quantum-limit noise performance. This work should facilitate the development of quantum information processing and integrated superconducting circuit design.

Efficient and stable wireless power transfer based on the non-Hermitian physics

Chao Zeng(曾超), Zhiwei Guo(郭志伟), Kejia Zhu(祝可嘉), Caifu Fan(范才富), Guo Li(李果), Jun Jiang(江俊), Yunhui Li(李云辉), Haitao Jiang(江海涛), Yaping Yang(羊亚平), Yong Sun(孙勇), and Hong Chen(陈鸿)

Chin. Phys. B, 2022, 31 (1): 010307. DOI: 10.1088/1674-1056/ac3815

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As one of the most attractive non-radiative power transfer mechanisms without cables, efficient magnetic resonance wireless power transfer (WPT) in the near field has been extensively developed in recent years, and promoted a variety of practical applications, such as mobile phones, medical implant devices and electric vehicles. However, the physical mechanism behind some key limitations of the resonance WPT, such as frequency splitting and size-dependent efficiency, is not very clear under the widely used circuit model. Here, we review the recently developed efficient and stable resonance WPT based on non-Hermitian physics, which starts from a completely different avenue (utilizing loss and gain) to introduce novel functionalities to the resonance WPT. From the perspective of non-Hermitian photonics, the coherent and incoherent effects compete and coexist in the WPT system, and the weak stable of energy transfer mainly comes from the broken phase associated with the phase transition of parity-time symmetry. Based on this basic physical framework, some optimization schemes are proposed, including using nonlinear effect, using bound states in the continuum, or resorting to the system with high-order parity-time symmetry. Moreover, the combination of non-Hermitian physics and topological photonics in multi-coil system also provides a versatile platform for long-range robust WPT with topological protection. Therefore, the non-Hermitian physics can not only exactly predict the main results of current WPT systems, but also provide new ways to solve the difficulties of previous designs.

Non-Hermitian Weyl semimetals: Non-Hermitian skin effect and non-Bloch bulk-boundary correspondence

Xiaosen Yang(杨孝森), Yang Cao(曹阳), and Yunjia Zhai(翟云佳)

Chin. Phys. B, 2022, 31 (1): 010308. DOI: 10.1088/1674-1056/ac3738

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We investigate novel features of three-dimensional non-Hermitian Weyl semimetals, paying special attention to the unconventional bulk-boundary correspondence. We use the non-Bloch Chern numbers as the tool to obtain the topological phase diagram, which is also confirmed by the energy spectra from our numerical results. It is shown that, in sharp contrast to Hermitian systems, the conventional (Bloch) bulk-boundary correspondence breaks down in non-Hermitian topological semimetals, which is caused by the non-Hermitian skin effect. We establish the non-Bloch bulk-boundary correspondence for non-Hermitian Weyl semimetals: the topological edge modes are determined by the non-Bloch Chern number of the bulk bands. Moreover, these topological edge modes can manifest as the unidirectional edge motion, and their signatures are consistent with the non-Bloch bulk-boundary correspondence. Our work establishes the non-Bloch bulk-boundary correspondence for non-Hermitian topological semimetals.

Two-body exceptional points in open dissipative systems

Peize Ding(丁霈泽) and Wei Yi(易为)

Chin. Phys. B, 2022, 31 (1): 010309. DOI: 10.1088/1674-1056/ac3396

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We study two-body non-Hermitian physics in the context of an open dissipative system depicted by the Lindblad master equation. Adopting a minimal lattice model of a handful of interacting fermions with single-particle dissipation, we show that the non-Hermitian effective Hamiltonian of the master equation gives rise to two-body scattering states with state- and interaction-dependent parity-time transition. The resulting two-body exceptional points can be extracted from the trace-preserving density-matrix dynamics of the same dissipative system with three atoms. Our results not only demonstrate the interplay of parity-time symmetry and interaction on the exact few-body level, but also serve as a minimal illustration on how key features of non-Hermitian few-body physics can be probed in an open dissipative many-body system.

Topological properties of non-Hermitian Creutz ladders

Hui-Qiang Liang(梁辉强) and Linhu Li(李林虎)

Chin. Phys. B, 2022, 31 (1): 010310. DOI: 10.1088/1674-1056/ac3991

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We study topological properties of the one-dimensional Creutz ladder model with different non-Hermitian asymmetric hoppings and on-site imaginary potentials, and obtain phase diagrams regarding the presence and absence of an energy gap and in-gap edge modes. The non-Hermitian skin effect (NHSE), which is known to break the bulk-boundary correspondence (BBC), emerges in the system only when the non-Hermiticity induces certain unbalanced non-reciprocity along the ladder. The topological properties of the model are found to be more sophisticated than that of its Hermitian counterpart, whether with or without the NHSE. In one scenario without the NHSE, the topological winding is found to exist in a two-dimensional plane embedded in a four-dimensional space of the complex Hamiltonian vector. The NHSE itself also possesses some unusual behaviors in this system, including a high spectral winding without the presence of long-range hoppings, and a competition between two types of the NHSE, with the same and opposite inverse localization lengths for the two bands, respectively. Furthermore, it is found that the NHSE in this model does not always break the conventional BBC, which is also associated with whether the band gap closes at exceptional points under the periodic boundary condition.

Disorder in parity-time symmetric quantum walks

Peng Xue(薛鹏)

Chin. Phys. B, 2022, 31 (1): 010311. DOI: 10.1088/1674-1056/ac3741

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We experimentally investigate the impact of static disorder and dynamic disorder on the non-unitary dynamics of parity-time (PT)-symmetric quantum walks. Via temporally alternating photon losses in an interferometric network, we realize the passive PT-symmetric quantum dynamics for single photons. Controllable coin operations allow us to simulate different environmental influences, which result in three different behaviors of quantum walkers: a standard ballistic spread, a diffusive behavior, and a localization, respectively, in a PT-symmetric quantum walk architecture.

Topology of a parity-time symmetric non-Hermitian rhombic lattice

Shumai Zhang(张舒迈), Liang Jin(金亮), and Zhi Song(宋智)

Chin. Phys. B, 2022, 31 (1): 010312. DOI: 10.1088/1674-1056/ac364a

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We investigate the topological properties of a trimerized parity-time ($ \mathcal{PT}$) symmetric non-Hermitian rhombic lattice. Although the system is $\mathcal{PT}$-symmetric, the topology is not inherited from the Hermitian lattice; in contrast, the topology can be altered by the non-Hermiticity and depends on the couplings between the sublattices. The bulk-boundary correspondence is valid and the Bloch bulk captures the band topology. Topological edge states present in the two band gaps and are predicted from the global Zak phase obtained through the Wilson loop approach. In addition, the anomalous edge states compactly localize within two diamond plaquettes at the boundaries when all bands are flat at the exceptional point of the lattice. Our findings reveal the topological properties of the $\mathcal{PT}$-symmetric non-Hermitian rhombic lattice and shed light on the investigation of multi-band non-Hermitian topological phases.

Exact solutions of non-Hermitian chains with asymmetric long-range hopping under specific boundary conditions

Cui-Xian Guo(郭翠仙) and Shu Chen(陈澍)

Chin. Phys. B, 2022, 31 (1): 010313. DOI: 10.1088/1674-1056/ac3228

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We study the one-dimensional general non-Hermitian models with asymmetric long-range hopping and explore how to analytically solve the systems under some specific boundary conditions. Although the introduction of long-range hopping terms prevents us from finding analytical solutions for arbitrary boundary parameters, we identify the existence of exact solutions when the boundary parameters fulfill some constraint relations, which give the specific boundary conditions. Our analytical results show that the wave functions take simple forms and are independent of hopping range, while the eigenvalue spectra display rich model-dependent structures. Particularly, we find the existence of a special point coined as pseudo-periodic boundary condition, for which the eigenvalues are the same as those of the periodical system when the hopping parameters fulfill certain conditions, whereas the eigenstates display the non-Hermitian skin effect.

Dynamical learning of non-Markovian quantum dynamics

Jintao Yang(杨锦涛), Junpeng Cao(曹俊鹏), and Wen-Li Yang(杨文力)

Chin. Phys. B, 2022, 31 (1): 010314. DOI: 10.1088/1674-1056/ac2490

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We study the non-Markovian dynamics of an open quantum system with machine learning. The observable physical quantities and their evolutions are generated by using the neural network. After the pre-training is completed, we fix the weights in the subsequent processes thus do not need the further gradient feedback. We find that the dynamical properties of physical quantities obtained by the dynamical learning are better than those obtained by the learning of Hamiltonian and time evolution operator. The dynamical learning can be applied to other quantum many-body systems, non-equilibrium statistics and random processes.

Nonlinear dynamics analysis of cluster-shaped conservative flows generated from a generalized thermostatted system

Yue Li(李月), Zengqiang Chen(陈增强), Zenghui Wang(王增会), and Shijian Cang(仓诗建)

Chin. Phys. B, 2022, 31 (1): 010501. DOI: 10.1088/1674-1056/ac0a61

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The thermostatted system is a conservative system different from Hamiltonian systems, and has attracted much attention because of its rich and different nonlinear dynamics. We report and analyze the multiple equilibria and curve axes of the cluster-shaped conservative flows generated from a generalized thermostatted system. It is found that the cluster-shaped structure is reflected in the geometry of the Hamiltonian, such as isosurfaces and local centers, and the shapes of cluster-shaped chaotic flows and invariant tori rely on the isosurfaces determined by initial conditions, while the numbers of clusters are subject to the local centers solved by the Hessian matrix of the Hamiltonian. Moreover, the study shows that the cluster-shaped chaotic flows and invariant tori are chained together by curve axes, which are the segments of equilibrium curves of the generalized thermostatted system. Furthermore, the interesting results are vividly demonstrated by the numerical simulations.

A new simplified ordered upwind method for calculating quasi-potential

Qing Yu(虞晴) and Xianbin Liu(刘先斌)

Chin. Phys. B, 2022, 31 (1): 010502. DOI: 10.1088/1674-1056/ac140f

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We present a new method for calculation of quasi-potential, which is a key concept in the large deviation theory. This method adopts the "ordered" idea in the ordered upwind algorithm and different from the finite difference upwind scheme, the first-order line integral is used as its update rule. With sufficient accuracy, the new simplified method can greatly speed up the computational time. Once the quasi-potential has been computed, the minimum action path (MAP) can also be obtained. Since the MAP is of concern in most stochastic situations, the effectiveness of this new method is checked by analyzing the accuracy of the MAP. Two cases of isotropic diffusion and anisotropic diffusion are considered. It is found that this new method can both effectively compute the MAPs for systems with isotropic diffusion and reduce the computational time. Meanwhile anisotropy will affect the accuracy of the computed MAP.

Explosive synchronization in a mobile network in the presence of a positive feedback mechanism

Dong-Jie Qian(钱冬杰)

Chin. Phys. B, 2022, 31 (1): 010503. DOI: 10.1088/1674-1056/ac16d3

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Synchronization is a process that describes the coherent dynamics of a large ensemble of interacting units. The study of explosive synchronization transition attracts considerable attention. Here, I report the explosive transition within the framework of a mobile network, while each oscillator is controlled by global-order parameters of the system. Using numerical simulation, I find that the explosive synchronization (ES) transition behavior can be controlled by simply adjusting the fraction of controlled oscillators. The influences of some parameters on explosive synchronization are studied. Moreover, due to the presence of the positive feedback mechanism, I prevent the occurrence of the synchronization of continuous-phase transition and make phase transition of the system a first-order phase transition accompanied by a hysteresis loop.

An extended smart driver model considering electronic throttle angle changes with memory

Congzhi Wu(武聪智), Hongxia Ge(葛红霞), and Rongjun Cheng(程荣军)

Chin. Phys. B, 2022, 31 (1): 010504. DOI: 10.1088/1674-1056/ac0eec

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Based on the fact that the electronic throttle angle effect performs well in the traditional car following model, this paper attempts to introduce the electronic throttle angle into the smart driver model (SDM) as an acceleration feedback control term, and establish an extended smart driver model considering electronic throttle angle changes with memory (ETSDM). In order to show the practicability of the extended model, the next generation simulation (NGSIM) data was used to calibrate and evaluate the extended model and the smart driver model. The calibration results show that, compared with SDM, the simulation value based on the ETSDM is better fitted with the measured data, that is, the extended model can describe the actual traffic situation more accurately. Then, the linear stability analysis of ETSDM was carried out theoretically, and the stability condition was derived. In addition, numerical simulations were explored to show the influence of the electronic throttle angle changes with memory and the driver sensitivity on the stability of traffic flow. The numerical results show that the feedback control term of electronic throttle angle changes with memory can enhance the stability of traffic flow, which shows the feasibility and superiority of the proposed model to a certain extent.

Large-amplitude dust acoustic solitons in an opposite polarity dusty plasma with generalized polarization force

Mahmood A. H. Khaled, Mohamed A. Shukri, and Yusra A. A. Hager

Chin. Phys. B, 2022, 31 (1): 010505. DOI: 10.1088/1674-1056/ac0421

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Linear and nonlinear dust acoustic (DA) waves have been investigated in an opposite polarity dusty plasma comprising negatively and positively charged dust grains, Maxwellian electrons and ions, including the generalized polarization force effect. The properties of linear DA waves have been significantly altered by the dual dust polarity and polarization force. Large amplitude DA solitons have been discussed in the framework of the Sagdeev potential technique. Our results show that both rarefactive and compressive solitons can exist in such a dusty plasma. The basic features of the Sagdeev potential have been examined under the effect of the polarization force parameter R, the ratio of the charge number of the positive dust to that of the negative dust Z, and the Mach number M. The results show that these parameters play a significant role in determining the region of existence of large amplitude DA solitons.

Effect of staggered array structure on the flow field of micro gas chromatographic column

Daohan Ge(葛道晗), Zhou Hu(胡州), Liqiang Zhang(张立强), and Shining Zhu(祝世宁)

Chin. Phys. B, 2022, 31 (1): 010701. DOI: 10.1088/1674-1056/ac0902

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A new design of staggered array semi-packed micro gas chromatographic column was presented based on the micro electromechanical system (MEMS) technology. It was a sensor for gas sample analysis. The internal velocity fields of ten types of semi-packed micro gas chromatographic column were studied. The effects of array spacing and dislocation spacing on the flow field distribution were investigated. The results show that on the basis of ensuring the formation of virtual wall, with the increase of array spacing, the maximum velocity difference between the flow channels in the vertical direction decreases gradually, but the velocity difference in the flow channels a and b increases. When the inlet velocity was set to be 0.18 m/s, the maximum velocity difference in the channel of the staggered semi-packed micro gas chromatography column 3 (CSAC3) was 0.05610 m/s. The maximum velocity difference in the channel a was 0.09160 m/s. The maximum velocity difference in the channel b was 0.02401 m/s. CSAC3 had a more uniform velocity field distribution, which can effectively suppress the laminar flow effect during chromatographic separation, and had a smaller pressure distribution, which puts forward lower requirements for carrier gas system. The staggered array semi-packed micro gas chromatography column proposed in this paper can effectively improve the velocity field distribution and pressure distribution in the channel, and provide a theoretical basis for the design of the new micro gas chromatography column structure.

Instantaneous frequency measurement using two parallel I/Q modulators based on optical power monitoring

Chuangye Wang(王创业), Tigang Ning(宁提纲), Jing Li(李晶), Li Pei(裴丽), Jingjing Zheng(郑晶晶), and Jingchuan Zhang(张景川)

Chin. Phys. B, 2022, 31 (1): 010702. DOI: 10.1088/1674-1056/ac1923

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A scheme for instantaneous frequency measurement (IFM) using two parallel I/Q modulators based on optical power monitoring is proposed. The amplitude comparison function (ACF) can be constructed to establish the relationship between the frequency of radio frequency (RF) signal and the power ratio of two optical signals output by two I/Q modulators. The frequency of RF signal can be derived by measuring the optical power of the optical signals output by two I/Q modulators. The measurement range and measurement error can be adjusted by controlling the delay amount of the electrical delay line. The feasibility of the scheme is verified, and the corresponding measurement range and measurement error of the system under different delay amounts of the electrical delay line are given. Compared with previous IFM schemes, the structure of this scheme is simple. Polarization devices, a photodetector and an electrical power meter are not used, which reduces the impact of the environmental disturbance on the system and the cost of the system. In simulation, the measurement range can reach 0 GHz-24.5 GHz by adjusting the delay amount of the electrical delay line τ =20 ps. The measurement error of the scheme is better at low frequency, and the measurement error of low frequency 0 GHz-9.6 GHz can reach -0.1 GHz to +0.05 GHz.

M1 transition energy and rate in the ground configuration of Ag-like ions with 62 ≤ Z ≤ 94 ^Hot!

Ju Meng(孟举), Wen-Xian Li(李文显), Ji-Guang Li(李冀光), Ze-Qing Wu(吴泽清), Jun Yan(颜君), Yong Wu(吴勇), and Jian-Guo Wang(王建国)

Chin. Phys. B, 2022, 31 (1): 013101. DOI: 10.1088/1674-1056/ac1333

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Systematic calculations and assessments are performed for the magnetic dipole (M1) transition energies and rates between the $^{2}\!F^{\rm o}_{5/2},_{7/2} $ levels in the ground configuration {4d}$^{10}${4f} along the Ag-like isoelectronic sequence with ${62 } \le Z \le { 94}$ based on the second-order many-body perturbation theory implemented in the Flexible Atomic Code. The electron correlations, Breit interaction and quantum electrodynamics effects are taken into account in the present calculations. The accuracy and reliability of our results are evaluated through comprehensive comparisons with available measurements and other theoretical results. For transition energies, our results are in good agreement with the recent experimental data obtained from the electron beam ion traps within 0.18%. The maximum discrepancy between our results and those obtained with the large-scale multiconfiguration Dirac-Hartee-Fock calculations by Grumer et al. [Phys. Rev. A 89 062501 (2014)] is less than 0.13 % along the isoelectronic sequence. Furthermore, the corresponding M1 transition rates are also reported. The present results can be used as the benchmark and useful for spectra simulation and diagnostics of astrophysical and fusion plasmas.

Solving the time-dependent Schrödinger equation by combining smooth exterior complex scaling and Arnoldi propagator

Shun Wang(王顺) and Wei-Chao Jiang(姜维超)

Chin. Phys. B, 2022, 31 (1): 013201. DOI: 10.1088/1674-1056/ac11d6

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We develop a highly efficient scheme for numerically solving the three-dimensional time-dependent Schrödinger equation of the single-active-electron atom in the field of laser pulses by combining smooth exterior complex scaling (SECS) absorbing method and Arnoldi propagation method. Such combination has not been reported in the literature. The proposed scheme is particularly useful in the applications involving long-time wave propagation. The SECS is a wonderful absorber, but its application results in a non-Hermitian Hamiltonian, invalidating propagators utilizing the Hermitian symmetry of the Hamiltonian. We demonstrate that the routine Arnoldi propagator can be modified to treat the non-Hermitian Hamiltonian. The efficiency of the proposed scheme is checked by tracking the time-dependent electron wave packet in the case of both weak extreme ultraviolet (XUV) and strong infrared (IR) laser pulses. Both perfect absorption and stable propagation are observed.

Influence of Coulomb force between two electrons on double ionization of He-like atoms

Peipei Liu(刘培培), Yongfang Li(李永芳), and Jingtao Zhang(张敬涛)

Chin. Phys. B, 2022, 31 (1): 013202. DOI: 10.1088/1674-1056/ac0cdf

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In strong-field double ionization, two electrons are ionized by intense laser field. These two electrons move in the laser field and the state is described by a Coulomb-Volkov state, where the repulsive Coulomb state describes the relative motion of the two electrons and the Volkov state describes the center-of-mass motion of the two electrons in the laser field. In the frame of scattering theory, we derive a simple analytical formula of the double ionization of He-like atoms. The effect of the Coulomb force between two electrons on the double ionization process is discussed. Numerical studies disclose that the Coulomb force enhances the ionization rate of high-energy electrons but suppresses the ionization rate of the lowest-energy electrons.

Electron-impact ionization cross section calculations for lithium-like ions

Guo-Jie Bian(卞国杰), Jyh-Ching Chang(张稚卿), Ke-Ning Huang(黄克宁), Chen-Sheng Wu(武晨晟), Yong-Jun Cheng(程勇军), Kai Wang(王凯), and Yong Wu(吴勇)

Chin. Phys. B, 2022, 31 (1): 013401. DOI: 10.1088/1674-1056/ac229e

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The electron-impact ionization of lithium-like ions C³⁺, N⁴⁺, O⁵⁺, Ne⁷⁺, and Fe²³⁺ is studied using a combination of two-potential distorted-wave and R-matrix methods with a relativistic correction. Total cross sections are computed for incident energies from 1 to 10 times of ionization energy and better agreements with the experimental results are obtained in comparison with the theoretical data available. It is found that the indirect ionization processes become significant for the incident energy larger than about four times of the ionization energy. Contributions from the exchange effects along the isoelectronic sequence are also discussed and found to be important. The present method can be used to obtain systematic ionization cross sections for highly charged ions across a wide incident energy range.

Tunable terahertz transmission behaviors and coupling mechanism in hybrid MoS₂ metamaterials Suggested by editors

Yuwang Deng(邓雨旺), Qingli Zhou(周庆莉), Wanlin Liang(梁菀琳), Pujing Zhang(张朴婧), and Cunlin Zhang(张存林)

Chin. Phys. B, 2022, 31 (1): 014101. DOI: 10.1088/1674-1056/ac1fde

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A hybrid metamaterial with the integration of molybdenum disulfide (MoS₂) overlayer is proposed to manipulate the terahertz (THz) wave. The simulated results indicate that the introduction of MoS₂ layer could significantly modify the resonant responses with large resonance red-shift and bandwidth broadening due to the depolarization field effect, especially for the structure on the small permitivity substrate. Additionally, the wide-band modulator in off-resonant region and a switch effect at resonance can be achieved by varying the conductivity of MoS₂ layer. Further theoretical calculations based on the Lorentz coupling model are consistent with the simulated results, explicating the response behaviors originate from the coupling between MoS₂ overlayer and the metastructure. Our results could provide a possibility for active control THz modulator and switchable device based on the MoS₂ overlayer and advance the understanding of the coupling mechanism in hybrid structures.

High-confinement ultra-wideband bandpass filter using compact folded slotline spoof surface plasmon polaritons Suggested by editors

Xue-Wei Zhang(张雪伟), Shao-Bin Liu(刘少斌), Ling-Ling Wang(王玲玲), Qi-Ming Yu (余奇明), Jian-Lou(娄健), and Shi-Ning Sun(孙世宁)

Chin. Phys. B, 2022, 31 (1): 014102. DOI: 10.1088/1674-1056/ac22a2

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A novel bandpass filter (BPF) based on spoof surface plasmon polaritons (SSPPs) using a compact folded slotline structure is proposed and experimentally demonstrated. The proposed novel SSPPs structure compared with a conventional plasmonic waveguide with slot line SSPPs unit structure at the same size, the considerable advantages in much lower asymptotic frequency with tight field confinement, which enable the proposed filter to be more miniaturization. A high-efficient mode conversion structure is designed to transition from TE-mode to SSPPs-mode by gradient slotline lengths. The low-frequency stop-band can be committed with microstrip to slotline evolution on both sides of the dielectric, while the high-frequency cutoff band is realized by the proposed SSPPs structure. The influence of dispersion relation, electric field distribution, surface current, and structural parameters on the transmission characteristics of the proposed BPF are analyzed by finite difference time domain (FDTD). To validate the design concept, the prototype of the miniaturized SSPPs BPF has been manufactured and measured. The experimental results show high performance of the fabricated sample, in which the working in a range of 0.9 GHz-5.2 GHz with the relative bandwidth is 142%, the insertion loss less than 0.5 dB, the reflection coefficient less than -10 dB, and the group delay is less than one ns. This works provides a mirror for realizing the miniaturization of waveguides, and the application and development of high-confinement SSPPs functional devices in the microwave and THz regimes.

Bandwidth-tunable silicon nitride microring resonators

Jiacheng Liu(刘嘉成), Chao Wu(吴超), Gongyu Xia(夏功榆), Qilin Zheng(郑骑林), Zhihong Zhu(朱志宏), and Ping Xu(徐平)

Chin. Phys. B, 2022, 31 (1): 014201. DOI: 10.1088/1674-1056/ac2e64

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We designed a reconfigurable dual-interferometer coupled silicon nitride microring resonator. By tuning the integrated heater on interferometer's arms, the "critical coupling" bandwidth of resonant mode is continuously adjustable whose quality factor varies from 7.9×10⁴ to 1.9×10⁵ with the extinction ratio keeping higher than 25 dB. Also a variety of coupling spanning from "under-coupling" to "over-coupling" were achieved, showing the ability to tune the quality factor from 6.0×10³ to 2.3×10⁵. Our design can provide an adjustable filtering method on silicon nitride photonic chip and contribute to optimize the nonlinear process for quantum photonics and all-optical signal processing.

High-efficiency asymmetric diffraction based on PT-antisymmetry in quantum dot molecules

Guangling Cheng(程广玲), Yongsheng Hu(胡永升), Wenxue Zhong(钟文学), and Aixi Chen(陈爱喜)

Chin. Phys. B, 2022, 31 (1): 014202. DOI: 10.1088/1674-1056/ac0422

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We present preparation of asymmetric grating with higher diffraction efficiency in quantum dot molecules by combining the tunneling effect and parity-time antisymmetry. In the presence of tunneling between two quantum dots, the system exhibits the striking PT antisymmetry via spatially modulating the driving field and the detuning with respect to the driven transition. For this reason, the asymmetric grating could be achieved. The results show that the diffraction efficiency can be adjustable via changing the driving intensity, detuning, tunneling strength, and interaction length, and then the high-order diffraction can be reached. The scheme provides a feasible way to obtain the direction-controlled diffraction grating, which can be helpful for optical information processing and realization of controllable optical self-image.

Propagation dynamics of dipole breathing wave in lossy nonlocal nonlinear media

Jian-Li Guo(郭建丽), Zhen-Jun Yang(杨振军), Xing-Liang Li(李星亮), and Shu-Min Zhang(张书敏)

Chin. Phys. B, 2022, 31 (1): 014203. DOI: 10.1088/1674-1056/ac032c

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In the framework of nonlinear wave optics, we report the evolution process of a dipole breathing wave in lossy nonlocal nonlinear media based on the nonlocal nonlinear Schrödinger equation. The analytical expression of the dipole breathing wave in such a nonlinear system is obtained by using the variational method. Taking advantage of the analytical expression, we analyze the influences of various physical parameters on the breathing wave propagation, including the propagation loss and the input power on the beam width, the beam intensity, and the wavefront curvature. Also, the corresponding analytical solutions are obtained. The validity of the analysis results is verified by numerical simulation. This study provides some new insights for investigating beam propagation in lossy nonlinear media.

High-energy picosecond single-pass multi-stage optical parametric generator and amplifier

Yang Yu(余洋), Zhao Liu(刘钊), Ke Liu(刘可), Chao Ma(马超), Hong-Wei Gao(高宏伟), Xiao-Jun Wang(王小军), Yong Bo(薄勇), Da-Fu Cui(崔大复), and Qin-Jun Peng(彭钦军)

Chin. Phys. B, 2022, 31 (1): 014204. DOI: 10.1088/1674-1056/abff46

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We demonstrate a new management of multi-stage optical parametric generator (OPG) and amplifier (OPA) to obtain high-energy picosecond sources with high beam quality. The setup of multi-stage OPG-OPA requires mode-matching between the pump beam and the stable mode of the OPG-OPA. In a proof-of-principle experiment, the single-pass multi-stage OPG-OPA consists of three walk-off compensated KTP crystal pairs and two lenses, pumped by an 86 ps, 1064 nm 10 kHz picosecond laser. The signal light at ~1.77 μm has an average output power of 502 mW with record energy up to 50.2 μJ. The beam quality factor of the signal light can be improved to $M_{x}^{2} \times M_{y}^{2}=1.87\times 2.16$ after filtering out about 40% signal power. To the best of our knowledge, it is the first picosecond single-pass multi-stage OPG-OPA pumped at kHz regime.

Photonic spin Hall effect and terahertz gas sensor via InSb-supported long-range surface plasmon resonance

Jie Cheng(程杰), Gaojun Wang(王高俊), Peng Dong(董鹏), Dapeng Liu(刘大鹏), Fengfeng Chi(迟逢逢), and Shengli Liu(刘胜利)

Chin. Phys. B, 2022, 31 (1): 014205. DOI: 10.1088/1674-1056/ac192a

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The photonic spin Hall effect (SHE), featured by a spin-dependent transverse shift of left- and right-handed circularly polarized light, holds great potential for applications in optical sensors, precise metrology and nanophotonic devices. In this paper, we present the significant enhancement of photonic SHE in the terahertz range by considering the InSb-supported long-range surface plasmon resonance (LRSPR) effect. The influences of the InSb/ENZ layer thickness and temperature on the photonic SHE were investigated. With the optimal structural parameters and temperature, the maximal spin shift of the horizontal polarization light can reach up to 2.68 mm. Moreover, the spin shift is very sensitive to the refractive index change of gas, and thus a terahertz gas sensing device with a superior intensity sensitivity of 2.5×10⁵ μm/RIU is proposed. These findings provide an effective method to enhance the photonic SHE in the terahertz range and therefore offer the opportunity for developing the terahertz optical sensors based on photonic SHE.

Plasmonic sensor with self-reference capability based on functional layer film composed of Au/Si gratings

Jiankai Zhu(朱剑凯), Xiangxian Wang(王向贤), Yunping Qi(祁云平), and Jianli Yu(余建立)

Chin. Phys. B, 2022, 31 (1): 014206. DOI: 10.1088/1674-1056/ac1335

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We propose a simple one-dimensional grating coupling system that can excite multiple surface plasmon resonances for refractive index (RI) sensing with self-reference characteristics in the near-infrared band. Using theoretical analysis and the finite-difference time-domain method, the plasmonic mechanism of the structure is discussed in detail. The results show that the excited resonances are independent of each other and have different fields of action. The mode involving extensive interaction with the analyte environment achieves a high sensitivity of 1236 nm/RIU, and the figure of merit (FOM) can reach 145 RIU^-1. Importantly, the mode that is insensitive to the analyte environment exhibits good self-reference characteristics. Moreover, we discuss the case of exchanging the substrate material with the analyte environment. Promising simulation results show that this RI sensor can be widely deployed in unstable and complicated environments.

Wavelength and sensitivity tunable long period gratings fabricated in fluid-cladding microfibers ^Hot!

Wa Jin(金娃), Linke Zhang(张林克), Xiang Zhang(张祥), Ming Xu(徐铭), Weihong Bi(毕卫红), and Yuefeng Qi(齐跃峰)

Chin. Phys. B, 2022, 31 (1): 014207. DOI: 10.1088/1674-1056/ac3394

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We report the fabrication of long period gratings in fluid-cladding microfibers by directly focusing a femtosecond laser beam on the microfibers surface to induce periodical modification a long one side of the microfibers. A long period grating is fabricated in a water-cladding microfiber with a diameter of ～ 5 μm, which demonstrates a resonant attenuation of 28.53 dB at wavelength of 1588.1 nm with 10 pitches. When water cladding is changed to be refractive index oil of n=1.33 and alcohol solution with concentration of 5%, the resonance wavelength shifts to 1575.1 nm with resonant attenuation of 24.91 dB and 1594.1 nm with resonant attenuation of 35.9 dB, respectively. The long period grating demonstrates different temperature sensitivities of -0.524 nm/℃, -0.767 nm/℃ and -1.316 nm/℃ for water, alcohol solution and refractive index oil cladding microfibers, respectively, which means the alterable liquid cladding allows the availability of tunable wavelength and sensitivity. The fluid-cladding protects the microfibers from external disturbance and contamination and allows more flexibility in controlling the transmission property and sensing characteristics of long period gratings, which can be used as fiber devices and sensors for chemical, biological, and environmental applications.

Topological phases and type-II edge state in two-leg-coupled Su-Schrieffer-Heeger chains Suggested by editors

Tianqi Luo(罗天琦), Xin Guan(关欣), Jingtao Fan(樊景涛), Gang Chen(陈刚), and Suo-Tang Jia(贾锁堂)

Chin. Phys. B, 2022, 31 (1): 014208. DOI: 10.1088/1674-1056/ac3650

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Topological quantum states have attracted great attention both theoretically and experimentally. Here, we show that the momentum-space lattice allows us to couple two Su-Schrieffer-Heeger (SSH) chains with opposite dimerizations and staggered interleg hoppings. The coupled SSH chain is a four-band model which has sublattice symmetry similar to the SSH4. Interestingly, the topological edge states occupy two sublattices at the same time, which can be regarded as a one-dimension analogue of the type-II corner state. The analytical expressions of the edge states are also obtained by solving the eigenequations. Finally, we provide a possible experimental scheme to detect the topological winding number and corresponding edge states.

Brightening single-photon emitters by combining an ultrathin metallic antenna and a silicon quasi-BIC antenna Suggested by editors

Shangtong Jia(贾尚曈), Zhi Li(李智), and Jianjun Chen(陈建军)

Chin. Phys. B, 2022, 31 (1): 014209. DOI: 10.1088/1674-1056/ac248c

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Bright single-photon emitters (SPEs) are fundamental components in many quantum applications. However, it is difficult to simultaneously get large Purcell enhancements and quantum yields in metallic nanostructures because of the huge losses in the metallic nanostructures. Herein, we propose to combine an ultrathin metallic bowtie antenna with a silicon antenna above a metallic substrate to simultaneously get large Purcell enhancements, quantum yields, and collection efficiencies. As a result, the brightness of SPEs in the hybrid nanostructure is greatly increased. Due to the deep subwavelength field confinement (mode size $ < 10$~nm) of surface plasmons in the ultrathin metallic film (thickness $<4 $~nm), the Purcell enhancement of the metallic bowtie antenna improves by more than 25 times when the metal thickness decreases from 20~nm to 2~nm. In the hybrid nanostructures by combining an ultrathin metallic bowtie antenna with a silicon antenna, the Purcell enhancement (Fp$\,\approx 2.6\times 10^{6})$ in the hybrid nanostructures is 63 times greater than those ($\le 4.1\times 10^{4}$) in the previous metallic and hybrid nanostructures. Because of the reduced ratio of electromagnetic fields in the ultrathin metallic bowtie antenna when the high-index silicon antenna is under the quasi-BIC state, a high quantum yield (QY$\,\approx 0.70$) is obtained. Moreover, the good radiation directivity of the quasi-BIC (bound state in the continuum) mode of the silicon antenna and the reflection of the metallic substrate result in a high collection efficiency (CE$\,\approx 0.71$). Consequently, the overall enhancement factor of brightness of a SPE in the hybrid nanostructure is EF$^{\ast }\approx {\rm Fp}\times {\rm QY}\times {\rm CE}\approx 1.3\times 10^{6}$, which is $5.6\times 10^{2}$ times greater than those (EF$^{\ast }\le 2.2\times 10^{3}$) in the previous metallic and hybrid nanostructures.

Hidden symmetry operators for asymmetric generalized quantum Rabi models Suggested by editors

Xilin Lu, Zi-Min Li, Vladimir V Mangazeev, and Murray T Batchelor

Chin. Phys. B, 2022, 31 (1): 014210. DOI: 10.1088/1674-1056/ac20c2

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The hidden $\mathbb{Z}_2$ symmetry of the asymmetric quantum Rabi model (AQRM) has recently been revealed via a systematic construction of the underlying symmetry operator. Based on the AQRM result, we propose an ansatz for the general form of the symmetry operators for AQRM-related models. Applying this ansatz we obtain the symmetry operator for three models: the anisotropic AQRM, the asymmetric Rabi--Stark model (ARSM), and the anisotropic ARSM.

Wideband switchable dual-functional terahertz polarization converter based on vanadium dioxide-assisted metasurface

De-Xian Yan(严德贤), Qin-Yin Feng(封覃银), Zi-Wei Yuan(袁紫微), Miao Meng(孟淼), Xiang-Jun Li(李向军), Guo-Hua Qiu(裘国华), and Ji-Ning Li(李吉宁)

Chin. Phys. B, 2022, 31 (1): 014211. DOI: 10.1088/1674-1056/ac05a7

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The terahertz technology has attracted considerable attention because of its potential applications in various fields. However, the research of functional devices, including polarization converters, remains a major demand for practical applications. In this work, a reflective dual-functional terahertz metadevice is presented, which combines two different polarization conversions through using a switchable metasurface. Different functions can be achieved because of the insulator-to-metal transition of vanadium dioxide (VO₂). At room temperature, the metadevice can be regarded as a linear-to-linear polarization convertor containing a gold circular split-ring resonator (CSRR), first polyimide (PI) spacer, continuous VO₂ film, second PI spacer, and gold substrate. The converter possesses a polarization conversion ratio higher than 0.9 and a bandwidth ratio of 81% in a range from 0.912 THz to 2.146 THz. When the temperature is above the insulator-to-metal transition temperature (approximately 68 ℃) and VO₂ becomes a metal, the metasurface transforms into a wideband linear-to-circular polarization converter composed of the gold CSRR, first PI layer, and continuous VO₂ film. The ellipticity is close to -1, while the axis ratio is lower than 3 dB in a range of 1.07 THz-1.67 THz. The metadevice also achieves a large angle tolerance and large manufacturing tolerance.

Research of NO₂ vertical profiles with look-up table method based on MAX-DOAS

Yingying Guo(郭映映), Suwen Li(李素文), Fusheng Mou(牟福生), Hexiang Qi(齐贺香), and Qijin Zhang(张琦锦)

Chin. Phys. B, 2022, 31 (1): 014212. DOI: 10.1088/1674-1056/ac1415

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Obtaining the vertical distribution profile of trace gas is of great significance for studying the diffusion procedure of air pollution. In this article, a look-up table method based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) technology is established for retrieving the tropospheric NO₂ vertical distribution profiles. This method retrieves the aerosol extinction profiles with minimum cost function. Then, the aerosol extinction profiles and the atmospheric radiation transfer model (RTM) are employed to establish the look-up table for retrieving the NO₂ vertical column densities (VCDs) and profiles. The measured NO₂ differential slant column densities (DSCDs) are compared with the NO₂ DSCDs simulated by the atmospheric RTM, and the NO₂ VCDs, the weight factor of NO₂ in the boundary layer, and the boundary layer height are obtained by the minimization process. The look-up table is established to retrieve NO₂ VCDs based on MAX-DOAS measurements in Huaibei area, and the results are compared with the data from Copernicus Atmospheric Monitoring Service (CAMS) model. It is found that there are nearly consistent and the correlation coefficient R² is more than 0.86. The results show that this technology provides a more convenient and accurate retrieval method for the stereoscopic monitoring of atmospheric environment.

A 515-nm laser-pumped idler-resonant femtosecond BiB₃O₆ optical parametric oscillator Suggested by editors

Jinfang Yang(杨金芳), Zhaohua Wang(王兆华), Jiajun Song(宋贾俊), Renchong Lv(吕仁冲), Xianzhi Wang(王羡之), Jiangfeng Zhu(朱江峰), and Zhiyi Wei(魏志义)

Chin. Phys. B, 2022, 31 (1): 014213. DOI: 10.1088/1674-1056/ac3813

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We report on an idler-resonant femtosecond optical parametrical oscillator (OPO) based on BiB₃O₆ (BiBO) crystal, synchronously pumped by a frequency-doubled, mode-locked Yb:KGW laser at 515 nm. The idler wavelengths of OPO can be tuned from 1100 nm to 1540 nm. At a repetition rate of 75.5 MHz, the OPO generates as much as 400 mW of idler power with 3.1 W of pump power, the corresponding pulse duration is 80 fs, which is 1.04 times of Fourier transform-limited (FTL) pulse duration at 1305 nm. In addition, the OPO exhibits excellent beam quality with M² < 1.8 at 1150 nm. To the best of our knowledge, this is the first idler-resonant femtosecond OPO pumped by 515 nm.

Lattice plasmon mode excitation via near-field coupling

Yun Lin(林蕴), Shuo Shen(申烁), Xiang Gao(高祥), and Liancheng Wang(汪炼成)

Chin. Phys. B, 2022, 31 (1): 014214. DOI: 10.1088/1674-1056/ac0523

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The optical response of metal nanoparticles can be modified through near-field or far-field interaction, yet the lattice plasmon modes (LPMs) considered can only be excited from the latter. Here instead, we present a theoretical evaluation for LPM excitation via the near-field coupling process. The sample is an arrayed structure with specific units composed of upper metal disks, a lower metal hole and a sandwiched dielectric post. The excitation process and underlying mechanism of the LPM and the influence of the structure parameters on the optical properties have been investigated in detail by using a finite-difference time-domain (FDTD) numerical method. Our investigation presented here should advance the understanding of near-field interaction of plasmon modes for LPM excitation, and LPMs could find some potential applications, such as in near-field optical microscopes, biosensors, optical filters and plasmonic lasers.

Anti-$\mathcal{PT}$-symmetric Kerr gyroscope

Huilai Zhang(张会来), Meiyu Peng(彭美瑜), Xun-Wei Xu(徐勋卫), and Hui Jing(景辉)

Chin. Phys. B, 2022, 31 (1): 014215. DOI: 10.1088/1674-1056/ac3988

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Non-Hermitian systems can exhibit unconventional spectral singularities called exceptional points (EPs). Various EP sensors have been fabricated in recent years, showing strong spectral responses to external signals. Here we propose how to achieve a nonlinear anti-parity-time ($\mathcal{APT}$) gyroscope by spinning an optical resonator. We show that, in the absence of any nonlinearity, the sensitivity or optical mode splitting of the linear device can be magnified up to 3 orders compared to that of the conventional device without EPs. Remarkably, the $\mathcal{APT}$ symmetry can be broken when including the Kerr nonlinearity of the materials and, as a result, the detection threshold can be significantly lowered, i.e., much weaker rotations which are well beyond the ability of a linear gyroscope can now be detected with the nonlinear device. Our work shows the powerful ability of $\mathcal{APT}$ gyroscopes in practice to achieve ultrasensitive rotation measurement.

Mode splitting and multiple-wavelength managements of surface plasmon polaritons in coupled cavities

Ping-Bo Fu(符平波) and Yue-Gang Chen(陈跃刚)

Chin. Phys. B, 2022, 31 (1): 014216. DOI: 10.1088/1674-1056/ac0e28

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Resonance cavity is a basic element in optics, which has wide applications in optical devices. Coupled cavities (CCs) designed in metal-insulator-metal (MIM) bus waveguide are investigated through the finite difference time domain method and coupled-mode theory. In the CCs, the resonant modes of the surface plasmon polaritons (SPPs) split with the thickness decreasing of the middle baffle. Through the coupled-mode theory analysis, it is found that the phase differences introduced in opposite and positive couplings between two cavities lead to mode splitting. The resonant wavelength of positive coupling mode can be tuned in a large range (about 644 nm) through adjusting the coupling strength, which is quite different from the classical adjustment of the optical path in a single cavity. Based on the resonances of the CCs in the MIM waveguide, more compact devices can be designed to manipulate SPPs propagation. A device is designed to realize flexible multiple-wavelength SPPs routing. The coupling in CC structures can be applied to the design of easy-integrated laser cavities, filters, multiple-wavelength management devices in SPPs circuits, nanosensors, etc.

Quality factor enhancement of plasmonic surface lattice resonance by using asymmetric periods

Yunjie Shi(石云杰), Lei Xiong(熊磊), Yuming Dong(董玉明), Degui Sun(孙德贵), and Guangyuan Li(李光元)

Chin. Phys. B, 2022, 31 (1): 014217. DOI: 10.1088/1674-1056/ac1332

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We report that using asymmetric lattice periods can enhance the quality factor of plasmonic surface lattice resonances (SLRs) in two-dimensional array of metal-insulator-metal nanopillars in asymmetric dielectric environment. Simulation results show that by adopting appropriate asymmetric lattice periods, the SLR quality factor can be enhanced by 24% compared with the scenario of symmetric periods. We find that the SLR quality factor is optimized when the resonance wavelength is closest to the Rayleigh cutoff wavelength. We also find that the SLRs effect is polarization sensitive in the proposed structure. We expect this work will advance the engineering of SLRs especially in asymmetric dielectric environments, and will promote their applications in sensing.

Microcrack localization using a collinear Lamb wave frequency-mixing technique in a thin plate

Ji-Shuo Wang(王积硕), Cai-Bin Xu(许才彬), You-Xuan Zhao(赵友选), Ning Hu(胡宁), and Ming-Xi Deng(邓明晰)

Chin. Phys. B, 2022, 31 (1): 014301. DOI: 10.1088/1674-1056/ac0da8

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A novel Lamb wave frequency-mixing technique is proposed for locating microcracks in a thin plate, which does not require the resonance condition of Lamb wave mixing and can accurately locate the microcracks through only one-time sensing. Based on the bilinear stress-strain constitutive model, a two-dimensional finite element (FE) model is built to investigate the frequency-mixing response induced by the interaction between two primary Lamb waves and a microcrack. When two primary Lamb waves of A0 and S0 modes with different frequencies excited on the same side of the plate simultaneously impinge on the examined microcrack, under the modulation of the contact acoustic nonlinearity, the microcrack itself can be deemed as the secondary sound source and it will radiate the Lamb waves of new combined frequencies. Based on the time of flight of the generated A0 mode at difference frequency, an indicator named normalized amplitude index (NAI) is defined to directly locate the multi-microcracks in the given plate. It is found that the number and location of the microcracks can be intuitively visualized by using the NAI based frequency-mixing technique. It is also demonstrated that the proposed frequency mixing technique is a promising approach for the microcrack localization.

Thermal apoptosis analysis considering injection behavior optimization and mass diffusion during magnetic hyperthermia

Yun-Dong Tang(汤云东), Jian Zou(邹建), Rodolfo C C Flesch(鲁道夫 C C 弗莱施), Tao Jin(金涛), and Ming-Hua He(何明华)

Chin. Phys. B, 2022, 31 (1): 014401. DOI: 10.1088/1674-1056/ac0819

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Thermally induced apoptosis for tumors depends mainly on the intrinsic characteristics of biological tissues as well as treatment temperature profile during magnetic hyperthermia. Further, treatment temperature distribution inside tumor depends on the injection behavior of irregular tumors, such as the injection dose and the injection location of nanofluids. In order to improve the treatment effect, the simulated annealing algorithm is adopted in this work to optimize the nanofluid injection behavior, and the improved Arrhenius model is used to evaluate the malignant ablations for three typical malignant tumor cell models. In addition, both the injection behavior optimization and the mass diffusion of nanofluid are both taken into consideration in order to improve the treatment effect. The simulation results demonstrate that the injection behavior can be optimized effectively by the proposed optimization method before therapy, the result of which can also conduce to improving the thermal apoptosis possibility for proposed typical malignant cells. Furthermore, an effective approach is also employed by considering longer diffusion duration and correct power dissipation at the same time. The results show that a better result can then be obtained than those in other cases when the power dissipation of MNPs is set to be Q_MNP=5.4×10⁷W·m³ and the diffusion time is 16 h.

Construction and mechanism analysis on nanoscale thermal cloak by in-situ annealing silicon carbide film Suggested by editors

Jian Zhang(张健), Hao-Chun Zhang(张昊春), Zi-Liang Huang(黄子亮), Wen-Bo Sun(孙文博), and Yi-Yi Li(李依依)

Chin. Phys. B, 2022, 31 (1): 014402. DOI: 10.1088/1674-1056/ac2809

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In recent years, there is a strong interest in thermal cloaking at the nanoscale, which has been achieved by using graphene and crystalline silicon films to build the nanoscale thermal cloak according to the classical macroscopic thermal cloak model. Silicon carbide, as a representative of the third-generation semiconductor material, has splendid properties, such as the high thermal conductivity and the high wear resistance. Therefore, in the present study, we build a nanoscale thermal cloak based on silicon carbide. The cloaking performance and the perturbation of the functional area to the external temperature filed are analyzed by the ratio of thermal cloaking and the response temperature, respectively. It is demonstrated that silicon carbide can also be used to build the nanoscale thermal cloak. Besides, we explore the influence of inner and outer radius on cloaking performance. Finally, the potential mechanism of the designed nanoscale thermal cloak is investigated by calculating and analyzing the phonon density of states (PDOS) and mode participation rate (MPR) within the structure. We find that the main reason for the decrease in the thermal conductivity of the functional area is phonon localization. This study extends the preparation method of nanoscale thermal cloaks and can provide a reference for the development of other nanoscale devices.

Three-dimensional clogging structures of granular spheres near hopper orifice Suggested by editors

Jing Yang(杨敬), Dianjinfeng Gong(宫殿锦丰), Xiaoxue Wang(汪晓雪), Zhichao Wang(王志超), Jianqi Li(李建奇), Bingwen Hu(胡炳文), and Chengjie Xia(夏成杰)

Chin. Phys. B, 2022, 31 (1): 014501. DOI: 10.1088/1674-1056/ac2f2f

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The characteristic clogging structures of granular spheres blocking three-dimensional granular flow through hopper outlet are analyzed based on packing structures reconstructed using magnetic resonance imaging techniques. Spheres in clogging structures are arranged in a way with typical features of load-bearing, such as more contacting bonds close to the horizontal plane and more mutually-stabilized contact configurations than packing structures away from the orifice. The requirement of load-bearing inevitably leads to the cooperativity of clogging structures with a correlation length of several particle diameters. This correlation length being comparable with the orifice diameter suggests that a clogging structure is composed of several mutually-stabilized structural motifs to span the orifice perimeter, instead of a collection of independent individual spheres to cover the whole orifice area. Accordingly, we propose a simple geometric model to explain the unexpected linear dependence of the average size of three-dimensional clogging structures on orifice diameter.

Characteristics of temperature fluctuation in two-dimensional turbulent Rayleigh-Bénard convection

Ming-Wei Fang(方明卫), Jian-Chao He(何建超), Zhan-Chao Hu(胡战超), and Yun Bao(包芸)

Chin. Phys. B, 2022, 31 (1): 014701. DOI: 10.1088/1674-1056/ac012f

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We study the characteristics of temperature fluctuation in two-dimensional turbulent Rayleigh-Bénard convection in a square cavity by direct numerical simulations. The Rayleigh number range is ${1\times }{{10}}^{{8}}\le Ra\le 1\times {{10}}^{{13}}$, and the Prandtl number is selected as $Pr=0.7$ and $Pr=4.3$. It is found that the temperature fluctuation profiles with respect to Ra exhibit two different distribution patterns. In the thermal boundary layer, the normalized fluctuation $\theta_{\rm rms}/\theta_{\rm rms,max}$ is independent of Ra and a power law relation is identified, $i.e.$, $\theta _{\rm rms}/\theta_{\rm rms,max}\sim \left( z / \delta \right)^{0.99\pm 0.01}$, where $z / \delta $ is a dimensionless distance to the boundary ($\delta $ is the thickness of thermal boundary layer). Out of the boundary layer, when $Ra\le 5\times {10}^{9}$, the profiles of $\theta _{\rm rms}/\theta_{\rm rms,max}$ descend, then ascend, and finally drop dramatically as $z / \delta $ increases. While for $Ra\ge 1\times {10}^{10}$, the profiles continuously decrease and finally overlap with each other. The two different characteristics of temperature fluctuations are closely related to the formation of stable large-scale circulations and corner rolls. Besides, there is a critical value of Ra indicating the transition, beyond which the fluctuation $\langle \theta_{\rm rms}\rangle _{V}$ has a power law dependence on Ra, given by $\langle \theta_{\rm rms}\rangle _{V}{\sim }{Ra}^{-0.14\pm 0.01}$.

Speedup of self-propelled helical swimmers in a long cylindrical pipe Suggested by editors

Ji Zhang(张骥), Kai Liu(刘凯), and Yang Ding(丁阳)

Chin. Phys. B, 2022, 31 (1): 014702. DOI: 10.1088/1674-1056/ac339a

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Pipe-like confinements are ubiquitously encountered by microswimmers. Here we systematically study the ratio of the speeds of a force- and torque-free microswimmer swimming in the center of a cylindrical pipe to its speed in an unbounded fluid (speed ratio). Inspired by E. coli, the model swimmer consists of a cylindrical head and a double-helical tail connected to the head by a rotating virtual motor. The numerical simulation shows that depending on swimmer geometry, confinements can enhance or hinder the swimming speed, which is verified by Reynolds number matched experiments. We further developed a reduced model. The model shows that the swimmer with a moderately long, slender head and a moderately long tail experiences the greatest speed enhancement, whereas the theoretical speed ratio has no upper limit. The properties of the virtual motor also affect the speed ratio, namely, the constant-frequency motor generates a greater speed ratio compared to the constant-torque motor.

In situ measurement on nonuniform velocity distributionin external detonation exhaust flow by analysis ofspectrum features using TDLAS

Xiao-Long Huang(黄孝龙), Ning Li(李宁), Chun-Sheng Weng(翁春生), and Yang Kang(康杨)

Chin. Phys. B, 2022, 31 (1): 014703. DOI: 10.1088/1674-1056/ac339b

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Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution. This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution, to provide a real-time and reliable measurement of velocity distribution in detonation exhaust flow with obvious nonuniformity. Relations are established between overlapped spectrums along probing beams and Gauss velocity distribution phantom according to the frequency shifts and tiny variations in components of light-of-sight absorbance profiles at low frequencies analyzed by the fast Fourier transform. With simulated optical measurement using H₂O feature at 7185.6 cm^-1 carried out on a phantom generated using a simulation of two-phase detonation by a two-fluid model, this method demonstrates a satisfying performance on recovery of velocity distribution profiles in supersonic flow even with a noise equivalent absorbance up to 2×10^-3. This method is applied to the analysis of rapidly decreasing velocity during a complete working cycle in the external flow field of an air-gasoline detonation tube operating at 25 Hz, and results show the velocity in the core flow field would be much larger than the arithmetic average from traditional tunable diode laser doppler velocimetry. This proposed velocity distribution sensor would reconstruct nonuniform velocity distribution of high-speed flow in low cost and simple operations, which broadens the possibility for applications in research on the formation and propagation of external flow filed of detonation tube.

Mechanism of microweld formation and breakage during Cu-Cu wire bonding investigated by molecular dynamics simulation

Beikang Gu(顾倍康), Shengnan Shen(申胜男), and Hui Li(李辉)

Chin. Phys. B, 2022, 31 (1): 016101. DOI: 10.1088/1674-1056/ac0e24

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Currently, wire bonding is the most popular first-level interconnection technology used between the die and package terminals, but even with its long-term and excessive usage, the mechanism of wire bonding has not been completely evaluated. Therefore, fundamental research is still needed. In this study, the mechanism of microweld formation and breakage during Cu-Cu wire bonding was investigated by using molecular dynamics simulation. The contact model for the nanoindentation process between the wire and substrate was developed to simulate the contact process of the Cu wire and Cu substrate. Elastic contact and plastic instability were investigated through the loading and unloading processes. Moreover, the evolution of the indentation morphology and distributions of the atomic stress were also investigated. It was shown that the loading and unloading curves do not coincide, and the unloading curve exhibited hysteresis. For the substrate, in the loading process, the main force changed from attractive to repulsive. The maximum von Mises stress increased and shifted from the center toward the edge of the contact area. During the unloading process, the main force changed from repulsive to attractive. The Mises stress reduced first and then increased. Stress concentration occurs around dislocations in the middle area of the Cu wire.

First-principles study of structural and opto-electronic characteristics of ultra-thin amorphous carbon films

Xiao-Yan Liu(刘晓艳), Lei Wang(王磊), and Yi Tong(童祎)

Chin. Phys. B, 2022, 31 (1): 016102. DOI: 10.1088/1674-1056/ac0cd8

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Most amorphous carbon (a-C) applications require films with ultra-thin thicknesses; however, the electronic structure and opto-electronic characteristics of such films remain unclear so far. To address this issue, we developed a theoretical model based on the density functional theory and molecular dynamic simulations, in order to calculate the electronic structure and opto-electronic characteristics of the ultra-thin a-C films at different densities and temperatures. Temperature was found to have a weak influence over the resulting electronic structure and opto-electronic characteristics, whereas density had a significant influence on these aspects. The volume fraction of sp³ bonding increased with density, whereas that of sp² bonding initially increased, reached a peak value of 2.52 g/cm³, and then decreased rapidly. Moreover, the extinction coefficients of the ultra-thin a-C films were found to be density-sensitive in the long-wavelength regime. This implies that switching the volume ratio of sp² to sp³ bonding can effectively alter the transmittances of ultra-thin a-C films, and this can serve as a novel approach toward photonic memory applications. Nevertheless, the electrical resistivity of the ultra-thin a-C films appeared independent of temperature. This implicitly indicates that the electrical switching behavior of a-C films previously utilized for non-volatile storage applications is likely due to an electrically induced effect and not a purely thermal consequence.

Polymorph selection of magnesium under different pressures: A simulation study

Wei Liu(刘维), Boqiang Wu(吴博强), Ze'an Tian(田泽安), Yunfei Mo(莫云飞), Tingfei Xi(奚廷斐), Zhiyi Wan(万子义), Rangsu Liu(刘让苏), and Hairong Liu(刘海蓉)

Chin. Phys. B, 2022, 31 (1): 016103. DOI: 10.1088/1674-1056/ac2e5e

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Molecular dynamics simulations were used to investigate the influence of pressure on the structural properties and dynamics of magnesium (Mg) during rapid solidification. The dynamics analysis revealed that, with an increase in pressure, the dynamics of Mg melt slowed down sharply and the dynamical heterogeneities increased, leading to a denser structure. Atom-level structural analysis using the cluster-type index method suggested that the predominant structure transformed from hexagonal closed-packed to face-centered cubic with increasing pressure from 0 GPa to 5 GPa, and then transformed to the A15 complex crystal structure as the pressure increased above 10 GPa. In addition, the nature of polymorph selection was investigated by analyzing the phonon dispersion of Mg under different pressures. These findings provide a novel insight into polymorphic transitions of Mg under pressure and guide the selection of Mg polymorphs for practical applications.

Pressure dependence of the thermal stability in LiMn₂O₄

Yan Zeng(曾彦), Hao Liang(梁浩), Shixue Guan(管诗雪), Junpu Wang(王俊普), Wenjia Liang(梁文嘉), Mengyang Huang(黄梦阳), and Fang Peng(彭放)

Chin. Phys. B, 2022, 31 (1): 016104. DOI: 10.1088/1674-1056/ac1932

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Structural stability in terms of the decomposition temperature in LiMn₂O₄ was systematically investigated by a series of high-temperature and high-pressure experiments. LiMn₂O₄ was found to have structural stability up to 5 GPa at room temperature. Under ambient pressure, the compound decomposed at 1300 ℃. The decomposition temperature decreased with increasing pressure, yielding more complex decomposed products. Below the decomposition temperature, the crystal structure of LiMn₂O₄ varied with pressure. The presented results in this study offer new insights into the thermal and pressure stability of LiMn₂O₄ materials as a cathode for lithium-ion batteries that can operate under extreme conditions. Therefore, these findings may serve as a useful guide for future work for improving lithium-ion batteries.

Spin and spin-orbit coupling effects in nickel-based superalloys: A first-principles study on Ni₃Al doped with Ta/W/Re

Liping Liu(刘立平), Jin Cao(曹晋), Wei Guo(郭伟), and Chongyu Wang(王崇愚)

Chin. Phys. B, 2022, 31 (1): 016105. DOI: 10.1088/1674-1056/ac4024

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Heavy elements (X= Ta/W/Re) play an important role in the performance of superalloys, which enhance the strength, anti-oxidation, creep resistance, and anti-corrosiveness of alloy materials in a high-temperature environment. In the present research, the heavy element doping effects in FCC-Ni(γ) and Ni₃Al(γ') systems are investigated in terms of their thermodynamic and mechanical properties, as well as electronic structures. The lattice constant, bulk modulus, elastic constant, and dopant formation energy in non-spin, spin polarized, and spin-orbit coupling (SOC) calculations are compared. The results show that the SOC effects are important in accurate electronic structure calculations for alloys with heavy elements. We find that including spin for both γ and γ' phases is necessary and sufficient for most cases, but the dopant formation energy is sensitive to different spin effects, for instance, in the absence of SOC, even spin-polarized calculations give 1% to 9% variance in the dopant formation energy in our model. Electronic structures calculations indicate that spin polarization causes a split in the metal d states, and SOC introduces a variance in the spin-up and spin-down states of the d states of heavy metals and reduces the magnetic moment of the system.

Probing structural and electronic properties of divalent metal Mg_n+1 and SrMg_n (n = 2–12) clusters and their anions

Song-Guo Xi(奚松国), Qing-Yang Li(李青阳), Yan-Fei Hu(胡燕飞), Yu-Quan Yuan(袁玉全), Ya-Ru Zhao(赵亚儒), Jun-Jie Yuan(袁俊杰), Meng-Chun Li(李孟春), and Yu-Jie Yang(杨雨杰)

Chin. Phys. B, 2022, 31 (1): 016106. DOI: 10.1088/1674-1056/ac04aa

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Divalent metal clusters have received great attention due to the interesting size-induced nonmetal-to-metal transition and fascinating properties dependent on cluster size, shape, and doping. In this work, the combination of the CALYPSO code and density functional theory (DFT) optimization is employed to explore the structural properties of neutral and anionic Mg_n+1 and SrMg_n (n=2-12) clusters. The results exhibit that as the atomic number of Mg increases, Sr atoms are more likely to replace Mg atoms located in the skeleton convex cap. By analyzing the binding energy, second-order energy difference and the charge transfer, it can be found the SrMg₉ cluster with tower framework presents outstanding stability in a studied size range. Further, bonding characteristic analysis reveals that the stability of SrMg₉ can be improved due to the strong s-p interaction among the atomic orbitals of Sr and Mg atoms.

Role of compositional changes on thermal, magnetic, and mechanical properties of Fe-P-C-based amorphous alloys Suggested by editors

Indah Raya, Supat Chupradit, Mustafa M Kadhim, Mustafa Z Mahmoud, Abduladheem Turki Jalil, Aravindhan Surendar, Sukaina Tuama Ghafel, Yasser Fakri Mustafa, and Alexander N Bochvar

Chin. Phys. B, 2022, 31 (1): 016401. DOI: 10.1088/1674-1056/ac3655

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This work aimed to tune the comprehensive properties of Fe-P-C-based amorphous system through investigating the role of microalloying process on the crystallization behavior, glass forming ability (GFA), soft magnetic features, and mechanical properties. Considering minor addition of elements into the system, it was found that the simultaneous microalloying of Ni and Co leads to the highest GFA, which was due to the optimization of compositional heterogeneity and creation of near-eutectic composition. Moreover, the FeCoNiCuPC amorphous alloy exhibited the best anelastic/viscoplastic behavior under the nanoindentation test, which was owing to the intensified structural fluctuations in the system. However, the improved plasticity by the extra Cu addition comes at the expense of magnetic properties, so that the saturation magnetization of this alloying system is significantly decreased compared to the FeCoPC amorphous alloy with the highest soft magnetic properties. In total, the results indicated that a combination of added elemental constitutes, i.e., Fe₆₉Co₅Ni₅Cu₁P₁₃C₇ composition, provides an optimized state for the comprehensive properties in the alloying system.

Observation of the BEC-BCS crossover in a degenerate Fermi gas of lithium atoms

Xiang-Chuan Yan(严祥传), Da-Li Sun(孙大立), Lu Wang(王璐), Jing Min(闵靖), Shi-Guo Peng(彭世国), and Kai-Jun Jiang(江开军)

Chin. Phys. B, 2022, 31 (1): 016701. DOI: 10.1088/1674-1056/ac0dae

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We observe characteristic atomic behaviors in the Bose-Einstein-condensation-Bardeen-Cooper-Schrieffer (BEC-BCS) crossover, by accurately tuning the magnetic field across the Feshbach resonance of lithium atoms. The magnetic field is calibrated by measuring the Zeeman shift of the optical transition. A non-monotonic anisotropic expansion is observed across the Feshbach resonance. The density distribution is explored in different interacting regimes, where a condensate of diatomic molecules forms in the BEC limit with the indication of a bimodal distribution. We also measure the three-body recombination atom loss in the BEC-BCS crossover, and find that the magnetic field of the maximum atom loss is in the BEC limit and gets closer to the Feshbach resonance when decreasing the atom temperature, which agrees with previous experiments and theoretical prediction. This work builds up a controllable platform for the study on the strongly interacting Fermi gas.

Observation of photon recoil effects in single-beam absorption spectroscopy with an ultracold strontium gas Suggested by editors

Fachao Hu(胡发超), Canzhu Tan(檀灿竹), Yuhai Jiang(江玉海), Matthias Weidemüller, and Bing Zhu(朱兵)

Chin. Phys. B, 2022, 31 (1): 016702. DOI: 10.1088/1674-1056/ac2486

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We report on observing photon recoil effects in the absorption of a single monochromatic light at 689 nm through an ultracold ⁸⁸Sr gas, where the recoil frequency is comparable to natural linewidth of the narrow-line transition 5s² ¹S₀-5s5p ³P₁ in strontium. In the regime of high-saturation, the absorption profile becomes asymmetric due to the photon-recoil shift, which is of the same order as the natural linewidth. The lineshape is described by an extension of the optical Bloch equations including the momentum transfers to atoms during emission and absorption of photons. Our work reveals the photon recoil effects in a simplest single-beam absorption setting, which is of significant relevance to other applications such as saturation spectroscopy, Ramsey interferometry, and absorption imaging.

Three-dimensional vertical ZnO transistors with suspended top electrodes fabricated by focused ion beam technology Suggested by editors

Chi Sun(孙驰), Linyuan Zhao(赵林媛), Tingting Hao(郝婷婷), Renrong Liang(梁仁荣), Haitao Ye(叶海涛), Junjie Li(李俊杰), and Changzhi Gu(顾长志)

Chin. Phys. B, 2022, 31 (1): 016801. DOI: 10.1088/1674-1056/ac34fe

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Three-dimensional (3D) vertical architecture transistors represent an important technological pursuit, which have distinct advantages in device integration density, operation speed, and power consumption. However, the fabrication processes of such 3D devices are complex, especially in the interconnection of electrodes. In this paper, we present a novel method which combines suspended electrodes and focused ion beam (FIB) technology to greatly simplify the electrodes interconnection in 3D devices. Based on this method, we fabricate 3D vertical core-double shell structure transistors with ZnO channel and Al₂O₃ gate-oxide both grown by atomic layer deposition. Suspended top electrodes of vertical architecture could be directly connected to planar electrodes by FIB deposited Pt nanowires, which avoid cumbersome steps in the traditional 3D structure fabrication technology. Both single pillar and arrays devices show well behaved transfer characteristics with an I_on/I_off current ratio greater than 10⁶ and a low threshold voltage around 0 V. The ON-current of the 2×2 pillars vertical channel transistor was 1.2 μA at the gate voltage of 3 V and drain voltage of 2 V, which can be also improved by increasing the number of pillars. Our method for fabricating vertical architecture transistors can be promising for device applications with high integration density and low power consumption.

Pressure- and temperature-dependent luminescence from Tm³⁺ ions doped in GdYTaO₄

Peng-Yu Zhou(周鹏宇), Xiu-Ming Dou(窦秀明), Bao-Quan Sun(孙宝权), Ren-Qin Dou(窦仁琴), Qing-Li Zhang(张庆礼), Bao Liu(刘鲍), Pu-Geng Hou(侯朴赓), Kai-Lin Chi(迟凯粼), and Kun Ding(丁琨)

Chin. Phys. B, 2022, 31 (1): 017101. DOI: 10.1088/1674-1056/ac0526

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Luminescent properties of Tm³⁺-doped GdYTaO₄ are studied for exploring their potential applications in temperature and pressure sensing. Two main emission peaks from ³H₄ $\to$ ³H₆ transition of Tm³⁺ are investigated. Intensity ratio between the two peaks evolves exponentially with temperature and has a highest sensitivity of 0.014 K^-1 at 32 K. The energy difference between the two peaks increases linearly with pressure increasing at a rate of 0.38 meV/GPa. Intensity ratio between the two peaks and their emission lifetimes are also analyzed for discussing the pressure-induced variation of the sample structure. Moreover, Raman spectra recorded under high pressures indicate an isostructural phase transition of GdYTaO₄ occurring at 4.46 GPa.

SU(3) spin-orbit coupled fermions in an optical lattice Suggested by editors

Xiaofan Zhou(周晓凡), Gang Chen(陈刚), and Suo-Tang Jia(贾锁堂)

Chin. Phys. B, 2022, 31 (1): 017102. DOI: 10.1088/1674-1056/ac11dc

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We propose a scheme to realize the SU(3) spin-orbit coupled three-component fermions in an one-dimensional optical lattice. The topological properties of the single-particle Hamiltonian are studied by calculating the Berry phase, winding number and edge state. We also investigate the effects of the interaction on the ground-state topology of the system, and characterize the interaction-induced topological phase transitions, using a state-of-the-art density-matrix renormalization-group numerical method. Finally, we show the typical features of the emerging quantum phases, and map out the many-body phase diagram between the interaction and the Zeeman field. Our results establish a way for exploring novel quantum physics induced by the SOC with SU(N) symmetry.

Defect calculations with quasiparticle correction: A revisited study of iodine defects in CH₃NH₃PbI₃ ^Hot!

Ling Li(李玲) and Wan-Jian Yin(尹万健)

Chin. Phys. B, 2022, 31 (1): 017103. DOI: 10.1088/1674-1056/ac3505

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Defect levels in semiconductor band gaps play a crucial role in functionalized semiconductors for practical applications in optoelectronics; however, first-principle defect calculations based on exchange-correlation functionals, such as local density approximation, grand gradient approximation (GGA), and hybrid functionals, either underestimate band gaps or misplace defect levels. In this study, we revisited iodine defects in CH₃NH₃PbI₃ by combining the accuracy of total energy calculations of GGA and single-electron level calculation of the GW method. The combined approach predicted neutral I_{m i} to be unstable and the transition level of I_{m i}(+1/-1) to be close to the valence band maximum. Therefore, I_{m i} may not be as detrimental as previously reported. Moreover, V_{m I} may be unstable in the -1 charged state but could still be detrimental owing to the deep transition level of V_{m I}(+1/0). These results could facilitate the further understanding of the intrinsic point defect and defect passivation observed in CH₃NH₃PbI₃.

First-principles study on improvement of two-dimensional hole gas concentration and confinement in AlN/GaN superlattices

Huihui He(何慧卉) and Shenyuan Yang(杨身园)

Chin. Phys. B, 2022, 31 (1): 017104. DOI: 10.1088/1674-1056/ac00a0

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Using first-principles calculations based on density functional theory, we have systematically studied the influence of in-plane lattice constant and thickness of slabs on the concentration and distribution of two-dimensional hole gas (2DHG) in AlN/GaN superlattices. We show that the increase of in-plane lattice constant would increase the concentration of 2DHG at interfaces and decrease the valence band offset, which may lead to a leak of current. Increasing the thickness of AlN and/or decreasing the thickness of GaN would remarkably strengthen the internal field in GaN layer, resulting in better confinement of 2DHG at AlN/GaN interfaces. Therefore, a moderate larger in-plane lattice constant and thicker AlN layer could improve the concentration and confinement of 2DHG at AlN/GaN interfaces. Our study could serve as a guide to control the properties of 2DHG at III-nitride interfaces and help to optimize the performance of p-type nitride-based devices.

Tri-hexagonal charge order in kagome metal CsV₃Sb₅ revealed by ¹²¹Sb nuclear quadrupole resonance

Chao Mu(牟超), Qiangwei Yin(殷蔷薇), Zhijun Tu(涂志俊), Chunsheng Gong(龚春生), Ping Zheng(郑萍), Hechang Lei(雷和畅), Zheng Li(李政), and Jianlin Luo(雒建林)

Chin. Phys. B, 2022, 31 (1): 017105. DOI: 10.1088/1674-1056/ac422c

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We report ¹²¹Sb nuclear quadrupole resonance (NQR) measurements on kagome superconductor CsV₃Sb₅ with T_c=2.5 K. ¹²¹Sb NQR spectra split after a charge density wave (CDW) transition at 94 K, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition. The CDW order exhibits tri-hexagonal deformation with a lateral shift between the adjacent kagome layers, which is consistent with 2×2×2 superlattice modulation. The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.

A density-wave-like transition in the polycrystalline V₃Sb₂ sample with bilayer kagome lattice

Ningning Wang(王宁宁), Yuhao Gu(顾雨豪), M. A. McGuire, Jiaqiang Yan, Lifen Shi(石利粉), Qi Cui(崔琦), Keyu Chen(陈科宇), Yuxin Wang(王郁欣), Hua Zhang(张华), Huaixin Yang(杨槐馨), Xiaoli Dong(董晓莉), Kun Jiang(蒋坤), Jiangping Hu(胡江平), Bosen Wang(王铂森), Jianping Sun(孙建平), and Jinguang Cheng(程金光)

Chin. Phys. B, 2022, 31 (1): 017106. DOI: 10.1088/1674-1056/ac4227

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Recently, transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum phenomena. Here we report on the synthesis, structure, and physical properties of a bilayer kagome lattice compound V₃Sb₂. The polycrystalline V₃Sb₂ samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850 ℃. Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at T_dw ≈ 160 K with a large thermal hysteresis, even though some sample-dependent behaviors were observed presumably due to the different preparation conditions. Upon cooling through T_dw, no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction measurements. This transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa, around which no sign of superconductivity was observed down to 1.5 K. Specific-heat measurements revealed a relatively large Sommerfeld coefficient γ = 18.5 mJ·mol^-1·K^-2, confirming the metallic ground state with moderate electronic correlations. Density functional theory calculations indicate that V₃Sb₂ shows a non-trivial topological crystalline property. Thus, our study makes V₃Sb₂ a new candidate of metallic kagome compound to study the interplay between density-wave-order, nontrivial band topology, and possible superconductivity.

Separating spins by dwell time of electrons across parallel double δ-magnetic-barrier nanostructure applied by bias

Sai-Yan Chen(陈赛艳), Mao-Wang Lu(卢卯旺), and Xue-Li Cao(曹雪丽)

Chin. Phys. B, 2022, 31 (1): 017201. DOI: 10.1088/1674-1056/abeb09

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The dwell time and spin polarization (SP) of electrons tunneling through a parallel double δ-magnetic-barrier nanostructure in the presence of a bias voltage is studied theoretically in this work. This nanostructure can be constructed by patterning two asymmetric ferromagnetic stripes on the top and bottom of InAs/Al_xIn_1-xAs heterostructure, respectively. An evident SP effect remains after a bias voltage is applied to the nanostructure. Moreover, both magnitude and sign of spin-polarized dwell time can be manipulated by properly changing the bias voltage, which may result in an electrically-tunable temporal spin splitter for spintronics device applications.

Dependence of short channel length on negative/positive bias temperature instability (NBTI/PBTI) for 3D FinFET devices Suggested by editors

Ren-Ren Xu(徐忍忍), Qing-Zhu Zhang(张青竹), Long-Da Zhou(周龙达), Hong Yang(杨红), Tian-Yang Gai(盖天洋), Hua-Xiang Yin(殷华湘), and Wen-Wu Wang(王文武)

Chin. Phys. B, 2022, 31 (1): 017301. DOI: 10.1088/1674-1056/ac1410

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A comprehensive study of the negative and positive bias temperature instability (NBTI/PBTI) of 3D FinFET devices with different small channel lengths is presented. It is found while with the channel lengths shrinking from 100 nm to 30 nm, both the NBTI characteristics of p-FinFET and PBTI characteristics of n-FinFET turn better. Moreover, the channel length dependence on NBTI is more serious than that on PBTI. Through the analysis of the physical mechanism of BTI and the simulation of 3-D stress in the FinFET device, a physical mechanism of the channel length dependence on NBTI/PBTI is proposed. Both extra fluorine passivation in the corner of bulk oxide and stronger channel stress in p-FinFETs with shorter channel length causes less NBTI issue, while the extra nitrogen passivation in the corner of bulk oxide induces less PBTI degradation as the channel length decreasing for n-FinFETs. The mechanism well matches the experimental result and provides one helpful guide for the improvement of reliability issues in the advanced FinFET process.

Spin transport properties for B-doped zigzag silicene nanoribbons with different edge hydrogenations

Jing-Fen Zhao(赵敬芬), Hui Wang(王辉), Zai-Fa Yang(杨在发), Hui Gao(高慧), Hong-Xia Bu(歩红霞), and Xiao-Juan Yuan(袁晓娟)

Chin. Phys. B, 2022, 31 (1): 017302. DOI: 10.1088/1674-1056/ac0795

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Exploring silicon-based spin modulating junction is one of the most promising areas of spintronics. Using nonequilibrium Green's function combined with density functional theory, a set of spin filters of hydrogenated zigzag silicene nanoribbons is designed by substituting a silicon atom with a boron one and the spin-correlated transport properties are studied. The results show that the spin polarization can be realized by structural symmetry breaking induced by boron doping. Remarkably, by tuning the edge hydrogenation, it is found that the spin filter efficiency can be varied from 30% to 58%. Moreover, it is also found and explained that the asymmetric hydrogenation can give rise to an obvious negative differential resistance which usually appears at weakly coupled junction. These findings indicate that the boron-doped ZSiNR is a promising material for spintronic applications.

Light focusing in linear arranged symmetric nanoparticle trimer on metal film system

Yuxia Tang(唐裕霞), Shuxia Wang(王蜀霞), Yingzhou Huang(黄映洲), and Yurui Fang(方蔚瑞)

Chin. Phys. B, 2022, 31 (1): 017303. DOI: 10.1088/1674-1056/ac20c3

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Benefiting from the induced image charge on film surface, the nanoparticle aggregating on metal exhibits interesting optical properties. In this work, a linear metal nanoparticle trimer on metal film system has been investigated to explore the novel optical phenomenon. Both the electric field and surface charge distributions demonstrate the light is focused on film greatly by the nanoparticles at two sides, which could be strongly modulated by the wavelength of incident light. And the influence of nanoparticle in middle on this light focusing ability has also been studied here, which is explained by the plasmon hybridization theory. Our finding about light focusing in nanoparticle aggregating on metal film not only enlarges the novel phenomenon of surface plasmon but also has great application prospect in the field of surface-enhanced spectra, surface catalysis, solar cells, water splitting, etc.

Study on a novel vertical enhancement-mode Ga₂O₃ MOSFET with FINFET structure

Liangliang Guo(郭亮良), Yuming Zhang(张玉明), Suzhen Luan(栾苏珍), Rundi Qiao(乔润迪), and Renxu Jia(贾仁需)

Chin. Phys. B, 2022, 31 (1): 017304. DOI: 10.1088/1674-1056/ac21c4

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A novel enhanced mode (E-mode) Ga₂O₃ metal-oxide-semiconductor field-effect transistor (MOSFET) with vertical FINFET structure is proposed and the characteristics of that device are numerically investigated. It is found that the concentration of the source region and the width coupled with the height of the channel mainly effect the on-state characteristics. The metal material of the gate, the oxide material, the oxide thickness, and the epitaxial layer concentration strongly affect the threshold voltage and the output currents. Enabling an E-mode MOSFET device requires a large work function gate metal and an oxide with large dielectric constant. When the output current density of the device increases, the source concentration, the thickness of the epitaxial layer, and the total width of the device need to be expanded. The threshold voltage decreases with the increase of the width of the channel area under the same gate voltage. It is indicated that a set of optimal parameters of a practical vertical enhancement-mode Ga₂O₃ MOSFET requires the epitaxial layer concentration, the channel height of the device, the thickness of the source region, and the oxide thickness of the device should be less than 5×10¹⁶ cm^-3, less than 1.5 μm, between 0.1 μm-0.3 μm and less than 0.08 μm, respectively.

Integer quantum Hall effect in Kekulé-patterned graphene

Yawar Mohammadi and Samira Bahrami

Chin. Phys. B, 2022, 31 (1): 017305. DOI: 10.1088/1674-1056/ac1b82

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Y-shaped Kekulé bond textures in a honeycomb lattice on a graphene-copper superlattice have recently been experimentally revealed. In this paper, the effects of such a bond modulation on the transport coefficients of Kekulé-patterned graphene are investigated in the presence of a perpendicular magnetic field. Analytical expressions are derived for the Hall and longitudinal conductivities using the Kubo formula. It is found that the Y-shaped Kekulé bond texture lifts the valley degeneracy of all Landau levels except that of the zero mode, leading to additional plateaus in the Hall conductivity accompanied by a split of the corresponding peaks in the longitudinal conductivity. Consequently, the Hall conductivity is quantized as ±ne²/h for n=2, 4, 6, 8, 10,..., excluding some plateaus that disappear due to the complete overlap of the Landau levels of different cones. These results also suggest that DC Hall conductivity measurements will allow us to determine the Kekulé bond texture amplitude.

Majorana zero modes, unconventional real-complex transition, and mobility edges in a one-dimensional non-Hermitian quasi-periodic lattice

Shujie Cheng(成书杰) and Xianlong Gao(高先龙)

Chin. Phys. B, 2022, 31 (1): 017401. DOI: 10.1088/1674-1056/ac3222

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A one-dimensional non-Hermitian quasiperiodic p-wave superconductor without $\mathcal{PT}$-symmetry is studied. By analyzing the spectrum, we discovered that there still exists real-complex energy transition even if the inexistence of $\mathcal{PT}$-symmetry breaking. By the inverse participation ratio, we constructed such a correspondence that pure real energies correspond to the extended states and complex energies correspond to the localized states, and this correspondence is precise and effective to detect the mobility edges. After investigating the topological properties, we arrived at a fact that the Majorana zero modes in this system are immune to the non-Hermiticity.

Cross correlation mediated by distant Majorana zero modes with no overlap

Lupei Qin(秦陆培), Wei Feng(冯伟), and Xin-Qi Li(李新奇)

Chin. Phys. B, 2022, 31 (1): 017402. DOI: 10.1088/1674-1056/ac1572

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Existing studies via shot noise calculation conclude that the cross correlation between the currents in the two leads connected by a pair of Majorana zero modes (MZMs) vanishes when their coupling energy $∊_{\rm M}\to 0$. Motivated by the intrinsic nature of nonlocality of the MZMs, we revisit this important problem and propose an experimental scheme to demonstrate the nonvanishing cross correlation even at the limit $∊^{}_{\rm M}\to 0$. The proposed scheme employs the Andreev-process-associated branch circuit currents, which are theoretically obtained by applying a decomposition analysis for the total currents while are accessible directly in practical measurement. For different bias voltage setup, we find intriguing results of both negative and positive correlations and carry out simple physical understanding using a quantum jump technique. Importantly, combining together with the evidence of the zero-bias-peak of conductance, the nonlocal cross correlation predicted in this work can help to confirm the existence of the nonlocal MZMs.

Superconductivity in octagraphene

Jun Li(李军) and Dao-Xin Yao(姚道新)

Chin. Phys. B, 2022, 31 (1): 017403. DOI: 10.1088/1674-1056/ac40fa

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This article reviews the basic theoretical aspects of octagraphene, an one-atom-thick allotrope of carbon, with unusual two-dimensional (2D) Fermi nesting, hoping to contribute to the new family of quantum materials. Octagraphene has an almost strongest sp² hybrid bond similar to graphene, and has the similar electronic band structure as iron-based superconductors, which makes it possible to realize high-temperature superconductivity. We have compared various possible mechanisms of superconductivity, including the unconventional s^± superconductivity driven by spin fluctuation and conventional superconductivity based on electron-phonon coupling. Theoretical studies have shown that octagraphene has relatively high structural stability. Although many 2D carbon materials with C₄ carbon ring and C₈ carbon ring structures have been reported, it is still challenging to realize the octagraphene with pure square-octagon structure experimentally. This material holds hope to realize new 2D high-temperature superconductivity.

Evolution of superconductivity and charge order in pressurized RbV₃Sb₅

Feng Du(杜锋), Shuaishuai Luo(罗帅帅), Rui Li(李蕊), Brenden R. Ortiz, Ye Chen(陈晔), Stephen D. Wilson, Yu Song(宋宇), and Huiqiu Yuan(袁辉球)

Chin. Phys. B, 2022, 31 (1): 017404. DOI: 10.1088/1674-1056/ac4232

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The kagome metals AV₃Sb₅ (A= K, Rb, Cs) under ambient pressure exhibit an unusual charge order, from which superconductivity emerges. In this work, by applying hydrostatic pressure using a liquid pressure medium and carrying out electrical resistance measurements for RbV₃Sb₅, we find that the charge order becomes suppressed under a modest pressure p_c (1.4 GPa<p_c<1.6 GPa), while the superconducting transition temperature T_c is maximized. T_c is then gradually weakened with further increase of pressure and reaches a minimum around 14.3 GPa, before exhibiting another {maximum} around 22.8 GPa, signifying the presence of a second superconducting dome. Distinct normal state resistance anomalies are found to be associated with the second superconducting dome, similar to KV₃Sb₅. Our findings point to qualitatively similar temperature-pressure phase diagrams in KV₃Sb₅ and RbV₃Sb₅, {and suggest a close link} between the second superconducting dome and the high-pressure resistance anomalies.

Pressure tuning of the anomalous Hall effect in the kagome superconductor CsV₃Sb₅

Fang-Hang Yu(喻芳航), Xi-Kai Wen(温茜凯), Zhi-Gang Gui(桂智刚), Tao Wu(吴涛), Zhenyu Wang(王震宇), Zi-Ji Xiang(项子霁), Jianjun Ying(应剑俊), and Xianhui Chen(陈仙辉)

Chin. Phys. B, 2022, 31 (1): 017405. DOI: 10.1088/1674-1056/ac3990

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Controlling the anomalous Hall effect (AHE) inspires potential applications of quantum materials in the next generation of electronics. The recently discovered quasi-2D kagome superconductor CsV₃Sb₅ exhibits large AHE accompanying with the charge-density-wave (CDW) order which provides us an ideal platform to study the interplay among nontrivial band topology, CDW, and unconventional superconductivity. Here, we systematically investigated the pressure effect of the AHE in CsV₃Sb₅. Our high-pressure transport measurements confirm the concurrence of AHE and CDW in the compressed CsV₃Sb₅. Remarkably, distinct from the negative AHE at ambient pressure, a positive anomalous Hall resistivity sets in below 35 K with pressure around 0.75 GPa, which can be attributed to the Fermi surface reconstruction and/or Fermi energy shift in the new CDW phase under pressure. Our work indicates that the anomalous Hall effect in CsV₃Sb₅ is tunable and highly related to the band structure.

Perpendicular magnetic anisotropy of Pd/Co₂MnSi/NiFe₂O₄/Pd multilayers on F-mica substrates Suggested by editors

Qingwang Bai(白青旺), Bin Guo(郭斌), Qin Yin(尹钦), and Shuyun Wang(王书运)

Chin. Phys. B, 2022, 31 (1): 017501. DOI: 10.1088/1674-1056/ac20cc

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Pd/Co₂MnSi (CMS)/NiFe₂O₄ (NFO)/Pd multilayers were fabricated on F-mica substrate by magnetron sputtering. The best PMA performance of the multilayer structure Pd(3 nm)/CMS(5 nm)/NFO(0.8 nm)/Pd(3 nm) was obtained by adjusting the thickness of the CMS and NFO layers. F-mica substrate has a flatter surface than glass and Si/SiO₂ substrate. The magnetic anisotropy energy density (K_eff) of the sample deposited on F-mica substrates is 0.6711 Merg/cm³ (1 erg = 10^-7 J), which is about 30% higher than that of the multilayer films deposited on glass (0.475 Merg/cm³) and Si/SiO₂ (0.511 Merg/cm³) substrates, and the R_Hall and H_C are also significantly increased. In this study, the NFO layer prepared by sputtering in the high purity Ar environment was exposed to the high purity O₂ atmosphere for 5 min, which can effectively eliminate the oxygen loss and oxygen vacancy in NFO, ensuring enough Co-O orbital hybridization at the interface of CMS/NFO, and thus effectively improve the sample PMA.

Probing the magnetization switching with in-plane magnetic anisotropy through field-modified magnetoresistance measurement ^Hot!

Runrun Hao(郝润润), Kun Zhang(张昆), Yinggang Li(李迎港), Qiang Cao(曹强), Xueying Zhang(张学莹), Dapeng Zhu(朱大鹏), and Weisheng Zhao(赵巍胜)

Chin. Phys. B, 2022, 31 (1): 017502. DOI: 10.1088/1674-1056/ac21bb

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Effective probing current-induced magnetization switching is highly required in the study of emerging spin-orbit torque (SOT) effect. However, the measurement of in-plane magnetization switching typically relies on the giant/tunneling magnetoresistance measurement in a spin valve structure calling for complicated fabrication process, or the non-electric approach of Kerr imaging technique. Here, we present a reliable and convenient method to electrically probe the SOT-induced in-plane magnetization switching in a simple Hall bar device through analyzing the MR signal modified by a magnetic field. In this case, the symmetry of MR is broken, resulting in a resistance difference for opposite magnetization orientations. Moreover, the feasibility of our method is widely evidenced in heavy metal/ferromagnet (Pt/Ni₂₀Fe₈₀ and W/Co₂₀Fe₆₀B₂₀) and the topological insulator/ferromagnet (Bi₂Se₃/Ni₂₀Fe₈₀). Our work simplifies the characterization process of the in-plane magnetization switching, which can promote the development of SOT-based devices.

Theoretical investigation of ferromagnetic resonance in a ferromagnetic thin film with external stress anisotropy

Jieyu Zhou(周婕妤), Jianhong Rong(荣建红), Huan Wang(王焕), Guohong Yun(云国宏), Yanan Wang(王娅男), and Shufei Zhang(张舒飞)

Chin. Phys. B, 2022, 31 (1): 017601. DOI: 10.1088/1674-1056/ac1b86

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We use the ferromagnetic resonance (FMR) method to study the properties of ferromagnetic thin film, in which external stress anisotropy, fourfold anisotropy and uniaxial anisotropy are considered. The analytical expressions of FMR frequency, linewidth and the imaginary part of magnetic susceptibility are obtained. Our results reveal that the FMR frequency and the imaginary part of magnetic susceptibility are distinctly enhanced, and the frequency linewidth or field linewidth are broadened due to a strong external stress anisotropy field. The hard-axis and easy-axis components of magnetization can be tuned significantly by controlling the intensity and direction of stress and the in-plane uniaxial anisotropy field.

Observation of source/drain bias-controlled quantum transport spectrum in junctionless silicon nanowire transistor Suggested by editors

Yang-Yan Guo(郭仰岩), Wei-Hua Han(韩伟华), Xiao-Di Zhang(张晓迪), Jun-Dong Chen(陈俊东), and Fu-Hua Yang(杨富华)

Chin. Phys. B, 2022, 31 (1): 017701. DOI: 10.1088/1674-1056/ac21ba

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We investigate the influence of source and drain bias voltages (V_DS) on the quantum sub-band transport spectrum in the 10-nm width N-typed junctionless nanowire transistor at the low temperature of 6 K. We demonstrate that the transverse electric field introduced from V_DS has a minor influence on the threshold voltage of the device. The transverse electric field plays the role of amplifying the gate restriction effect of the channel. The one-dimensional (1D)-band dominated transport is demonstrated to be modulated by V_DS in the saturation region and the linear region, with the sub-band energy levels in the channel (E_channel) intersecting with Fermi levels of the source (E_fS) and the drain (E_fD) in turn as V_g increases. The turning points from the linear region to the saturation region shift to higher gate voltages with V_DS increase because the higher Fermi energy levels of the channel required to meet the situation of E_fD =E_channel. We also find that the bias electric field has the effect to accelerate the thermally activated electrons in the channel, equivalent to the effect of thermal temperature on the increase of electron energy. Our work provides a detailed description of the bias-modulated quantum electronic properties, which will give a more comprehensive understanding of transport behavior in nanoscale devices.

Efficiency droop in InGaN/GaN-based LEDs with a gradually varying In composition in each InGaN well layer

Shang-Da Qu(屈尚达), Ming-Sheng Xu(徐明升), Cheng-Xin Wang(王成新), Kai-Ju Shi(时凯居), Rui Li(李睿), Ye-Hui Wei(魏烨辉), Xian-Gang Xu(徐现刚), and Zi-Wu Ji(冀子武)

Chin. Phys. B, 2022, 31 (1): 017801. DOI: 10.1088/1674-1056/ac0817

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Temperature-dependent and driving current-dependent electroluminescence spectra of two different InGaN/GaN multiple quantum well structures SA and SB are investigated, with the In composition in each well layer (WL) along the growth direction progressively increasing for SA and progressively decreasing for SB. The results show that SB exhibits an improved efficiency droop compared with SA. This phenomenon can be explained as follows: owing to the difference in growth pattern of the WL between these two samples, the terminal region of the WL in SB contains fewer In atoms than in SA, and therefore the former undergoes less In volatilization than the latter during the waiting period required for warming-up due to the difference in the growth temperature between well and barrier layers. This results in SB having a deeper triangular-shaped potential well in its WL than SA, which strongly confines the carriers to the initial region of the WL to prevent them from leaking to the p-GaN side, thus improving the efficiency droop. Moreover, the improvement in the efficiency droop for SB is also partly attributed to its stronger Coulomb screening effect and carrier localization effect.

Magnetic polaron-related optical properties in Ni(II)-doped CdS nanobelts: Implication for spin nanophotonic devices

Fu-Jian Ge(葛付建), Hui Peng(彭辉), Ye Tian(田野), Xiao-Yue Fan(范晓跃), Shuai Zhang(张帅), Xian-Xin Wu(吴宪欣), Xin-Feng Liu(刘新风), and Bing-Suo Zou(邹炳锁)

Chin. Phys. B, 2022, 31 (1): 017802. DOI: 10.1088/1674-1056/ac0782

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Emissions by magnetic polarons and spin-coupled d-d transitions in diluted magnetic semiconductors (DMSs) have become a popular research field due to their unusual optical behaviors. In this work, high-quality NiI₂(II)-doped CdS nanobelts are synthesized via chemical vapor deposition (CVD), and then characterized by scanning electron microscopy (SEM), x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and Raman scattering. At low temperatures, the photoluminescence (PL) spectra of the Ni-doped nanobelts demonstrate three peaks near the band edge: the free exciton (FX) peak, the exciton magnetic polaron (EMP) peak out of ferromagnetically coupled spins coupled with FXs, and a small higher-energy peak from the interaction of antiferromagnetic coupled Ni pairs and FXs, called antiferromagnetic magnetic polarons (AMPs). With a higher Ni doping concentration, in addition to the d-d transitions of single Ni ions at 620 nm and 760 nm, two other PL peaks appear at 530 nm and 685 nm, attributed to another EMP emission and the d-d transitions of the antiferromagnetic coupled Ni²⁺-Ni²⁺ pair, respectively. Furthermore, single-mode lasing at the first EMP is excited by a femtosecond laser pulse, proving a coherent bosonic lasing of the EMP condensate out of complicated states. These results show that the coupled spins play an important role in forming magnetic polaron and implementing related optical responses.

Uniform light emission from electrically driven plasmonic grating using multilayer tunneling barriers Suggested by editors

Xiao-Bo He(何小波), Hua-Tian Hu(胡华天), Ji-Bo Tang(唐继博), Guo-Zhen Zhang(张国桢), Xue Chen(陈雪), Jun-Jun Shi(石俊俊), Zhen-Wei Ou(欧振伟), Zhi-Feng Shi(史志锋), Shun-Ping Zhang(张顺平), Chang Liu(刘昌), and Hong-Xing Xu(徐红星)

Chin. Phys. B, 2022, 31 (1): 017803. DOI: 10.1088/1674-1056/ac248f

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Light emission by inelastic tunneling (LEIT) from a metal-insulator-metal tunnel junction is an ultrafast emission process. It is a promising platform for ultrafast transduction from electrical signal to optical signal on integrated circuits. However, existing procedures of fabricating LEIT devices usually involve both top-down and bottom-up techniques, which reduces its compatibility with the modern microfabrication streamline and limits its potential applications in industrial scale-up. Here in this work, we lift these restrictions by using a multilayer insulator grown by atomic layer deposition as the tunnel barrier. For the first time, we fabricate an LEIT device fully by microfabrication techniques and show a stable performance under ambient conditions. Uniform electroluminescence is observed over the entire active region, with the emission spectrum shaped by metallic grating plasmons. The introduction of a multilayer insulator into the LEIT can provide an additional degree of freedom for engineering the energy band landscape of the tunnel barrier. The presented scheme of preparing a stable ultrathin tunnel barrier may also find some applications in a wide range of integrated optoelectronic devices.

Demonstration of Faraday anomalous dispersion optical filter with reflection configuration

Yi Liu(刘艺), Baodong Yang(杨保东), Junmin Wang(王军民), Wenyi Huang(黄文艺), Zhiyu Gou(缑芝玉), and Haitao Zhou(周海涛)

Chin. Phys. B, 2022, 31 (1): 017804. DOI: 10.1088/1674-1056/ac229d

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A narrow linewidth Faraday anomalous dispersion optical filter (FADOF) with reflection configuration is achieved for the first time based on the cesium (Cs) ground state 6S_1/2 to the excited state 6P_3/2 transition at 852 nm. Compared with the conventional FADOF with transmission configuration, reflection-type FADOF can greatly improve the transmittance of optical filter under the same experimental parameters, because it allows signal light to go and return through the atomic vapor cell. In our experiment, peak transmittance at Cs 6S_1/2 F=4-6P_3/2 transition is 81% for the reflection-type FADOF, and while 54% for the transmission-type FADOF when the temperature of Cs vapor cell and the axial magnetic field are 60 ℃ and 19 G. The idea of this reflection-type FADOF design has the potential to be applied to the FADOF operating between two excited states to obtain higher transmittance.

Two different emission enhancement of trans-stilbene crystal under high pressure: Different evolution of structure

Yarong Gu(古雅荣), Guicheng Shao(邵贵成), Zhumei Tian(田竹梅), Haixia Li(李海霞), Kai Wang(王凯), and Bo Zou(邹勃)

Chin. Phys. B, 2022, 31 (1): 017901. DOI: 10.1088/1674-1056/ac20c4

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Mechanoresponsive luminescent (MRL) materials have drawn extensive concern due to their potential applications in mechanical sensors, memory chips, and security inks; especially these possessing high emission efficiency. In this work, we found trans-stilbene crystal exhibited two different pressure-induced emission enhancement (PIEE) behaviors at different pressure areas. The structural characterizations combined with density functional theory calculation indicate that the first emission enhancement was due to the decrease of nonradiation transition by the weaken of energy exchange process between atoms and lattice. And the second emission enhancement was attributed to the strengthen of C-H...C interactions from the non-planarization comformation. The results regarding the mechanoresponsive behavior of trans-stilbene offered a deep insight into PIEE from the structural point of view, which will facilitate the design of and search for high-performance MRL materials.

Removal of GaN film over AlGaN with inductively coupled BCl₃/Ar atomic layer etch

Jia-Le Tang(唐家乐) and Chao Liu(刘超)

Chin. Phys. B, 2022, 31 (1): 018101. DOI: 10.1088/1674-1056/ac032d

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Atomic layer etching (ALE) of thin film GaN (0001) is reported in detail using sequential surface modification by BCl₃ adsorption and removal of the modified surface layer by low energy Ar plasma exposure in a reactive ion etching system. The estimated etching rate of GaN is ～ 0.74 nm/cycle. The GaN is removed from the surface of AlGaN after 135 cycles. To study the mechanism of the etching, the detailed characterization and analyses are carried out, including scanning electron microscope (SEM), x-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM). It is found that in the presence of GaCl_x after surface modification by BCl₃, the GaCl_x disappears after having exposed to low energy Ar plasma, which effectively exhibits the mechanism of atomic layer etch. This technique enables a uniform and reproducible fabrication process for enhancement-mode high electron mobility transistors with a p-GaN gate.

Plasma assisted molecular beam epitaxial growth of GaN with low growth rates and their properties ^Hot!

Zhen-Hua Li(李振华), Peng-Fei Shao(邵鹏飞), Gen-Jun Shi(施根俊), Yao-Zheng Wu(吴耀政), Zheng-Peng Wang(汪正鹏), Si-Qi Li(李思琦), Dong-Qi Zhang(张东祺), Tao Tao(陶涛), Qing-Jun Xu(徐庆君), Zi-Li Xie(谢自力), Jian-Dong Ye(叶建东), Dun-Jun Chen(陈敦军), Bin Liu(刘斌), Ke Wang(王科), You-Dou Zheng(郑有炓), and Rong Zhang(张荣)

Chin. Phys. B, 2022, 31 (1): 018102. DOI: 10.1088/1674-1056/ac339d

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A systematic investigation on PA-MBE grown GaN with low growth rates (less than 0.2 μm/h) has been conducted in a wide growth temperature range, in order to guide future growth of sophisticated fine structures for quantum device applications. Similar to usual growths with higher growth rates, three growth regions have been revealed, namely, Ga droplets, slightly Ga-rich and N-rich 3D growth regions. The slightly Ga-rich region is preferred, in which GaN epilayers demonstrate optimal crystalline quality, which has been demonstrated by streaky RHEED patterns, atomic smooth surface morphology, and very low defect related yellow and blue luminescence bands. The growth temperature is a critical parameter to obtain high quality materials and the optimal growth temperature window (～ 700-760 ℃) has been identified. The growth rate shows a strong dependence on growth temperatures in the optimal temperature window, and attention must be paid when growing fine structures at a low growth rate. Mg and Si doped GaN were also studied, and both p- and n-type materials were obtained.

Synthesis and study the influence of yttrium doping on band structure, optical, non-linear optical and dielectric results for Ca₁₂Al₁₄O₃₃ (C12A7) single crystals grown using traveling-solvent floating zone (TSFZ) method

A. Abdel Moez, Ahmed I. Ali, and A. Tayel

Chin. Phys. B, 2022, 31 (1): 018103. DOI: 10.1088/1674-1056/ac0a5f

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Ca₁₂Al₁₄O₃₃ (C12A7) and Y_0.02Ca_11.98Al₁₄O₃₃ (Y-C12A7) single crystals were grown by using the traveling-solvent floating zone (TSFZ) method. The temperature was increased to avoid the bubbles and cracks which may be formed during the preparation of the ingot material. We have started with the flux higher than the normal to avoid the bubbles and make good treatment for the solid-liquid interface. The structures of both Ca₁₂Al₁₄O₃₃ (C12A7) and Y_0.02Ca_11.98Al₁₄O₃₃ (Y-C12A7) were studied by using x-ray diffraction (XRD). Optical properties for C12A7 and Y-C12A7 single crystals have been studied in order to determine the optical parameters such as optical energy gap (E_g), refractive index n, oscillating energy (E_o), dispersion energy (E_d), volume energy loss function (VELF), and surface energy loss function (SELF). Finally, a new result for these samples is that the third-order nonlinear optical susceptibility (χ⁽³⁾) was determined. The results have been discussed with effect of Y-doping on the C12A7 single crystals for optical and industrial applications.

Theoretical study on the exciton dynamics of coherent excitation energy transfer in the phycoerythrin 545 light-harvesting complex

Xue-Yan Cui(崔雪燕), Yi-Jing Yan(严以京), and Jian-Hua Wei(魏建华)

Chin. Phys. B, 2022, 31 (1): 018201. DOI: 10.1088/1674-1056/ac0bad

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The experimental observation of long-lived quantum coherence in the excitation energy transfer (EET) process of the several photosynthetic light-harvesting complexes at low and room temperatures has aroused hot debate. It challenges the common perception in the field of complicated pigment molecular systems and evokes considerable theoretical efforts to seek reasonable explanations. In this work, we investigate the coherent exciton dynamics of the phycoerythrin 545 (PE545) complex. We use the dissipation equation of motion to theoretically investigate the effect of the local pigment vibrations on the population transfer process. The result indicates that the realistic local pigment vibrations do assist the energy transmission. We demonstrate the coherence between different pigment molecules in the PE545 system is an essential ingredient in the EET process among various sites. The coherence makes the excitation energy delocalized, which leads to the redistribution of the excitation among all the chromophores in the steady state. Furthermore, we investigate the effects of the complex high-frequency spectral density function on the exciton dynamics and find that the high-frequency Brownian oscillator model contributes most to the exciton dynamic process. The discussions on the local pigment vibrations of the Brownian oscillator model suggest that the local heterogeneous protein environments and the effects of active vibration modes play a significant role in coherent energy transport.

Substrate tuned reconstructed polymerization of naphthalocyanine on Ag(110) ^Hot!

Qi Zheng(郑琦), Li Huang(黄立), Deliang Bao(包德亮), Rongting Wu(武荣庭), Yan Li(李彦), Xiao Lin(林晓), Shixuan Du(杜世萱), and Hong-Jun Gao(高鸿钧)

Chin. Phys. B, 2022, 31 (1): 018202. DOI: 10.1088/1674-1056/ac3500

Abstract ( 647 )

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The linkage structures between monomers make great influence on the properties of polymers. The synthesis of some special linkage structures can be challenging, which is often overcome by employing special reaction conditions. Here, we build dihydropentalene linkage in poly-naphthalocyanine on Ag(110) surface. Scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) measurements confirm the dihydropentalene linkage structure and a possible formation path with reconstruction steps is proposed. The controlled experiment on Ag(100) surface shows no dihydropentalene structures formed, which indicates the grooved substrate is necessary for the reconstruction. This work provides insights into the surface restricted reactions that can yield special structures in organic polymers.

Modeling and character analyzing of multiple fractional-order memcapacitors in parallel connection

Xiang Xu(徐翔), Gangquan Si(司刚全), Zhang Guo(郭璋), and Babajide Oluwatosin Oresanya

Chin. Phys. B, 2022, 31 (1): 018401. DOI: 10.1088/1674-1056/ac05b1

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Recently, the memory elements-based circuits have been addressed frequently in the nonlinear circuit theory due to their unique behaviors. Thus, the modeling and characterizing of the mem-elements become essential. In this paper, the analysis of the multiple fractional-order voltage-controlled memcapacitors model in parallel connection is studied. Firstly, two fractional-order memcapacitors are connected in parallel, the equivalent model is derived, and the characteristic of the equivalent memcapacitor is analyzed in positive or negative connection. Then a new understanding manner according to different rate factor K and fractional order α is derived to explain the equivalent modeling structure conveniently. Additionally, the negative order appears, which is a consequence of the combination of memcapacitors in different directions. Meanwhile, the equivalent parallel memcapacitance has been drawn to determine that multiple fractional-order memcapacitors could be calculated as one composite memcapacitor. Thus, an arbitrary fractional-order equivalent memcapacitor could be constructed by multiple fractional-order memcapacitors.

Sensitivity of heavy-ion-induced single event burnout in SiC MOSFET

Hong Zhang(张鸿), Hong-Xia Guo(郭红霞), Feng-Qi Zhang(张凤祁), Xiao-Yu Pan(潘霄宇), Yi-Tian Liu(柳奕天), Zhao-Qiao Gu(顾朝桥), An-An Ju(琚安安), and Xiao-Ping Ouyang(欧阳晓平)

Chin. Phys. B, 2022, 31 (1): 018501. DOI: 10.1088/1674-1056/ac051d

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The energy deposition and electrothermal behavior of SiC metal-oxide-semiconductor field-effect transistor (MOSFET) under heavy ion radiation are investigated based on Monte Carlo method and TCAD numerical simulation. The Monte Carlo simulation results show that the density of heavy ion-induced energy deposition is the largest in the center of the heavy ion track. The time for energy deposition in SiC is on the order of picoseconds. The TCAD is used to simulate the single event burnout (SEB) sensitivity of SiC MOSFET at four representative incident positions and four incident depths. When heavy ions strike vertically from SiC MOSFET source electrode, the SiC MOSFET has the shortest SEB time and the lowest SEB voltage with respect to direct strike from the epitaxial layer, strike from the channel, and strike from the body diode region. High current and strong electric field simultaneously appear in the local area of SiC MOSFET, resulting in excessive power dissipation, further leading to excessive high lattice temperature. The gate-source junction area and the substrate-epitaxial layer junction area are both the regions where the SiC lattice temperature first reaches the SEB critical temperature. In the SEB simulation of SiC MOSFET at different incident depths, when the incident depth does not exceed the device's epitaxial layer, the heavy-ion-induced charge deposition is not enough to make lattice temperature reach the SEB critical temperature.

Heterogeneous integration of InP HEMTs on quartz wafer using BCB bonding technology

Yan-Fu Wang(王彦富), Bo Wang(王博), Rui-Ze Feng(封瑞泽), Zhi-Hang Tong(童志航), Tong Liu(刘桐), Peng Ding(丁芃), Yong-Bo Su(苏永波), Jing-Tao Zhou(周静涛), Feng Yang(杨枫), Wu-Chang Ding(丁武昌), and Zhi Jin(金智)

Chin. Phys. B, 2022, 31 (1): 018502. DOI: 10.1088/1674-1056/ac05b2

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Heterogeneous integrated InP high electron mobility transistors (HEMTs) on quartz wafers are fabricated successfully by using a reverse-grown InP epitaxial structure and benzocyclobutene (BCB) bonding technology. The channel of the new device is In_0.7Ga_0.3As, and the gate length is 100 nm. A maximum extrinsic transconductance g_m,max of 855.5 mS/mm and a maximum drain current of 536.5 mA/mm are obtained. The current gain cutoff frequency is as high as 262 GHz and the maximum oscillation frequency reaches 288 GHz. In addition, a small signal equivalent circuit model of heterogeneous integration of InP HEMTs on quartz wafer is built to characterize device performance.

Voltage-controllable magnetic skyrmion dynamics for spiking neuron device applications

Ming-Min Zhu(朱明敏), Shu-Ting Cui(崔淑婷), Xiao-Fei Xu(徐晓飞), Sheng-Bin Shi(施胜宾), Di-Qing Nian(年迪青), Jing Luo(罗京), Yang Qiu(邱阳), Han Yang(杨浛), Guo-Liang Yu(郁国良), and Hao-Miao Zhou (周浩淼)

Chin. Phys. B, 2022, 31 (1): 018503. DOI: 10.1088/1674-1056/ac05b0

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Voltage-controlled magnetic skyrmions have attracted special attention because they satisfy the requirements for well-controlled high-efficiency and energy saving for future skyrmion-based neuron device applications. In this work, we propose a compact leaky-integrate-fire (LIF) spiking neuron device by using the voltage-driven skyrmion dynamics in a multiferroic nanodisk structure. The skyrmion dynamics is controlled by well tailoring voltage-induced piezostrains, where the skyrmion radius can be effectively modulated by applying the piezostrain pulses. Like the biological neuron, the proposed skyrmionic neuron will accumulate a membrane potential as skyrmion radius is varied by inputting the continuous piezostrain spikes, and the skyrmion radius will return to the initial state in the absence of piezostrain. Therefore, this skyrmion radius-based membrane potential will reach a definite threshold value by the strain stimuli and then reset by removing the stimuli. Such the LIF neuronal functionality and the behaviors of the proposed skyrmionic neuron device are elucidated through the micromagnetic simulation studies. Our results may benefit the utilization of skyrmionic neuron for constructing the future energy-efficient and voltage-tunable spiking neural networks.

A 3D SiC MOSFET with poly-silicon/SiC heterojunction diode

Sheng-Long Ran(冉胜龙), Zhi-Yong Huang(黄智勇), Sheng-Dong Hu(胡盛东), Han Yang(杨晗), Jie Jiang(江洁), and Du Zhou(周读)

Chin. Phys. B, 2022, 31 (1): 018504. DOI: 10.1088/1674-1056/ac0038

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A three-dimensional (3D) silicon-carbide (SiC) trench metal-oxide-semiconductor field-effect transistor (MOSFET) with a heterojunction diode (HJD-TMOS) is proposed and studied in this work. The SiC MOSFET is characterized by an HJD which is partially embedded on one side of the gate. When the device is in the turn-on state, the body parasitic diode can be effectively controlled by the embedded HJD, the switching loss thus decreases for the device. Moreover, a highly-doped P⁺ layer is encircled the gate oxide on the same side as the HJD and under the gate oxide, which is used to lighten the electric field concentration and improve the reliability of gate oxide layer. Physical mechanism for the HJD-TMOS is analyzed. Comparing with the conventional device with the same level of on-resistance, the breakdown voltage of the HJD-TMOS is improved by 23.4%, and the miller charge and the switching loss decrease by 43.2% and 48.6%, respectively.

Impact of symmetric gate-recess length on the DC and RF characteristics of InP HEMTs Suggested by editors

Ruize Feng(封瑞泽), Bo Wang(王博), Shurui Cao(曹书睿), Tong Liu(刘桐), Yongbo Su(苏永波), Wuchang Ding(丁武昌), Peng Ding(丁芃), and Zhi Jin(金智)

Chin. Phys. B, 2022, 31 (1): 018505. DOI: 10.1088/1674-1056/ac364d

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We fabricated a set of symmetric gate-recess devices with gate length of 70nm. We kept the source-to-drain spacing ($L_{SD}$) unchanged, and obtained a group of devices with gate-recess length $(L_{recess})$ from 0.4$\mu$m to 0.8$\mu$m through process improvement. In order to suppress the influence of the kink effect, we have done SiN$_{X}$ passivation treatment. The maximum saturation current density ($I_{D\_max}$) and maximum transconductance ($g_{m,max}$) increase as L_recess decreases to 0.4$\mu$m. At this time, the device shows $I_{D\_max}=749.6$mA/mm at $V_{GS}=0.2$V, $V_{DS}=1.5$V, and $g_{m\_max}=1111$mS/mm at $V_{GS}=-0.35$V, $V_{DS}=1.5$V. Meanwhile, as $L_{recess}$ increases, it causes parasitic capacitance $C_{gd}$ and $g_{d}$ to decrease, making $f_{max}$ drastically increases. When L_recess=0.8$\mu$m, the device shows $f_{T}=188$GHz and $f_{max}=1112$GHz.

A novel low-loss four-bit bandpass filter using RF MEMS switches

Lulu Han(韩路路), Yu Wang(王宇), Qiannan Wu(吴倩楠), Shiyi Zhang(张世义), Shanshan Wang(王姗姗), and Mengwei Li(李孟委)

Chin. Phys. B, 2022, 31 (1): 018506. DOI: 10.1088/1674-1056/ac1b95

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This paper details the design and simulation of a novel low-loss four-bit reconfigurable bandpass filter that integrates microelectromechanical system (MEMS) switches and comb resonators. A T-shaped reconfigurable resonator is reconfigured in a 'one resonator, multiple MEMS switches' configuration and used to gate the load capacitances of comb resonators so that a multiple-frequency filtering function is realized within the 7-16 GHz frequency range. In addition, the insertion loss of the filter is less than 1.99 dB, the out-of-band rejection is more than 18.30 dB, and the group delay is less than 0.25 ns. On the other hand, the size of this novel filter is only 4.4 mm×2.5 mm×0.4 mm. Our results indicate that this MEMS reconfigurable filter, which can switch 16 central frequency bands through eight switches, achieves a low insertion loss compared to those of traditional MEMS filters. In addition, the advantages of small size are obtained while achieving high integration.

Social bots and mass media manipulated public opinion through dual opinion climate

Chun Cheng(程纯), Yun Luo(罗云), Chang-bin Yu(于长斌), and Wei-ping Ding(丁卫平)

Chin. Phys. B, 2022, 31 (1): 018701. DOI: 10.1088/1674-1056/ac0baa

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Opinion dynamics models based on the multi-agent method commonly assume that interactions between individuals in a social network result in changes in their opinions. However, formation of public opinion in a social network is a macroscopic statistical result of opinions of all expressive individuals (corresponding to silent individuals). Therefore, public opinion can be manipulated not only by changing individuals' opinions, but also by changing their states of expression (or silence) which can be interpreted as the phenomenon "spiral of silence" in social psychology. Based on this theory, we establish a "dual opinion climate" model, involving social bots and mass media through a multi-agent method, to describe mechanism for manipulation of public opinion in social networks. We find that both social bots (as local variables) and mass media (as a global variable) can interfere with the formation of public opinion, cause a significant superposition effect when they act in the same direction, and inhibit each other when they act in opposite directions.

High efficiency ETM-free perovskite cell composed of CuSCN and increasing gradient CH₃NH₃PbI₃

Tao Wang(汪涛), Gui-Jiang Xiao(肖贵将), Ren Sun(孙韧), Lin-Bao Luo(罗林保), and Mao-Xiang Yi(易茂祥)

Chin. Phys. B, 2022, 31 (1): 018801. DOI: 10.1088/1674-1056/ac0bb0

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To enhance device performance and reduce fabrication cost, a series of electron transporting material (ETM)-free perovskite solar cells (PSCs) is developed by TCAD Atlas. The accuracy of the physical mode of PSCs is verified, due to the simulations of PEDOT:PSS-CH₃NH₃PbI₃-PCBM and CuSCN-CH₃NH₃PbI₃-PCBM p-i-n PSCs showing a good agreement with experimental results. Different hole transporting materials (HTMs) are selected and directly combined with n-CH₃NH₃PbI₃, and the CuSCN-CH₃NH₃PbI₃ is the best in these ETM-free PSCs. To further study the CuSCN-CH₃NH₃PbI₃ PSC, the influences of back electrode material, gradient band gap, thickness, doping concentration, and bulk defect density on the performance are investigated. Energy band and distribution of electric field are utilized to optimize the design. As a result, the efficiency of CuSCN-CH₃NH₃PbI₃ PSC is achieved to be 26.64%. This study provides the guideline for designing and improving the performances of ETM-free PSCs.

Cascading failures of overload behaviors using a new coupled network model between edges

Yu-Wei Yan(严玉为), Yuan Jiang(蒋沅), Rong-Bin Yu(余荣斌), Song-Qing Yang(杨松青), and Cheng Hong(洪成)

Chin. Phys. B, 2022, 31 (1): 018901. DOI: 10.1088/1674-1056/ac1337

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With the development of network science, the coupling between networks has become the focus of complex network research. However, previous studies mainly focused on the coupling between nodes, while ignored the coupling between edges. We propose a novel cascading failure model of two-layer networks. The model considers the different loads and capacities of edges, as well as the elastic and coupling relationship between edges. In addition, a more flexible load-capacity strategy is adopted to verify the model. The simulation results show that the model is feasible. Different networks have different behaviors for the same parameters. By changing the load parameters, capacity parameters, overload parameters, and distribution parameters reasonably, the robustness of the model can be significantly improved.

Information flow between stock markets: A Koopman decomposition approach Suggested by editors

Semba Sherehe, Huiyun Wan(万慧云), Changgui Gu(顾长贵), and Huijie Yang(杨会杰)

Chin. Phys. B, 2022, 31 (1): 018902. DOI: 10.1088/1674-1056/ac16c9

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Stock markets in the world are linked by complicated and dynamical relationships into a temporal network. Extensive works have provided us with rich findings from the topological properties and their evolutionary trajectories, but the underlying dynamical mechanism is still not in order. In the present work, we proposed a technical scheme to reveal the dynamical law from the temporal network. The index records for the global stock markets form a multivariate time series. One separates the series into segments and calculates the information flows between the markets, resulting in a temporal market network representing the state and its evolution. Then the technique of the Koopman decomposition operator is adopted to find the law stored in the information flows. The results show that the stock market system has a high flexibility, i.e., it jumps easily between different states. The information flows mainly from high to low volatility stock markets. And the dynamical process of information flow is composed of many dynamic modes distribute homogenously in a wide range of periods from one month to several ten years, but there exist only nine modes dominating the macroscopic patterns.

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