Chin. Phys. B

Solutions of novel soliton molecules and their interactions of (2 + 1)-dimensional potential Boiti-Leon-Manna-Pempinelli equation

Hong-Cai Ma(马红彩), Yi-Dan Gao(高一丹), and Ai-Ping Deng(邓爱平)

Chin. Phys. B, 2022, 31 (7): 070201. DOI: 10.1088/1674-1056/ac4cc0

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The method of variable separation has always been regarded as a crucial method for solving nonlinear evolution equations. In this paper, we use a new form of variable separation to study novel soliton molecules and their interactions in (2+1)-dimensional potential Boiti-Leon-Manna-Pempinelli equation. Dromion molecules, ring molecules, lump molecules, multi-instantaneous molecules, and their interactions are obtained. Then we draw corresponding images with maple software to study their dynamic behavior.

Propagation and modulational instability of Rossby waves in stratified fluids

Xiao-Qian Yang(杨晓倩), En-Gui Fan(范恩贵), and Ning Zhang(张宁)

Chin. Phys. B, 2022, 31 (7): 070202. DOI: 10.1088/1674-1056/ac4e0a

Abstract ( 351 )

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Perturbation analysis and scale expansion are used to derive the (2+1)-dimensional coupled nonlinear Schrödinger (CNLS) equations that can describe interactions of two Rossby waves propagating in stratified fluids. The (2+1)-dimensional equations can reflect and describe the wave propagation more intuitively and accurately. The properties of the two waves in the process of propagation can be analyzed by the solution obtained from the equations using the Hirota bilinear method, and the influence factors of modulational instability are analyzed. The results suggest that, when two Rossby waves with slightly different wave numbers propagate in the stratified fluids, the intensity of bright soliton decreases with the increases of dark soliton coefficients. In addition, the size of modulational instable area is related to the amplitude and wave number in y direction.

Effect of observation time on source identification of diffusion in complex networks

Chaoyi Shi(史朝义), Qi Zhang(张琦), and Tianguang Chu(楚天广)

Chin. Phys. B, 2022, 31 (7): 070203. DOI: 10.1088/1674-1056/ac5985

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This paper examines the effect of the observation time on source identification of a discrete-time susceptible-infected-recovered diffusion process in a network with snapshot of partial nodes. We formulate the source identification problem as a maximum likelihood (ML) estimator and develop a statistical inference method based on Monte Carlo simulation (MCS) to estimate the source location and the initial time of diffusion. Experimental results in synthetic networks and real-world networks demonstrate evident impact of the observation time as well as the fraction of the observers on the concerned problem.

Experimental study on gas production and solution composition during the interaction of femtosecond laser pulse and liquid

Yichun Wang(王奕淳), Han Wu(吴寒), Wenkang Lu(陆文康), Meng Li(李萌), Ling Tao(陶凌), and Xiuquan Ma(马修泉)

Chin. Phys. B, 2022, 31 (7): 070204. DOI: 10.1088/1674-1056/ac7449

Abstract ( 299 )

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The process of ionizing normal saline induced by femtosecond laser is studied from the perspective of gas production rate and composition. When the repetition rate is less than 1000 Hz, each laser pulse independently generates ionization gas. At the same time, we discovered the inhibitory effect of meglumini diatrizoici on the ionization process and explained the reasons for this inhibition. Finally, the gas composition proved that the primary gas production mechanism of the femtosecond laser is the decomposition of water molecular, and the composition of the solution after the reaction proved the decomposition effect of the laser on meglumine.

Topological phase transition in cavity optomechanical system with periodical modulation

Zhi-Xu Zhang(张志旭), Lu Qi(祁鲁), Wen-Xue Cui(崔文学), Shou Zhang(张寿), and Hong-Fu Wang(王洪福)

Chin. Phys. B, 2022, 31 (7): 070301. DOI: 10.1088/1674-1056/ac4a6a

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We investigate the topological phase transition and the enhanced topological effect in a cavity optomechanical system with periodical modulation. By calculating the steady-state equations of the system, the steady-state conditions of cavity fields and the restricted conditions of effective optomechanical couplings are demonstrated. It is found that the cavity optomechanical system can be modulated to different topological Su-Schrieffer-Heeger (SSH) phases via designing the optomechanical couplings legitimately. Meanwhile, combining the effective optomechanical couplings and the probability distributions of gap states, we reveal the topological phase transition between trivial SSH phase and nontrivial SSH phase via adjusting the decay rates of cavity fields. Moreover, we find that the enhanced topological effect of gap states can be achieved by enlarging the size of system and adjusting the decay rates of cavity fields.

Robustness of two-qubit and three-qubit states in correlated quantum channels

Zhan-Yun Wang(王展云), Feng-Lin Wu(吴风霖), Zhen-Yu Peng(彭振宇), and Si-Yuan Liu(刘思远)

Chin. Phys. B, 2022, 31 (7): 070302. DOI: 10.1088/1674-1056/ac4a61

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We investigate how the correlated actions of quantum channels affect the robustness of entangled states. We consider the Bell-like state and random two-qubit pure states in the correlated depolarizing, bit flip, bit-phase flip, and phase flip channels. It is found that the robustness of two-qubit pure states can be noticeably enhanced due to the correlations between consecutive actions of these noisy channels, and the Bell-like state is always the most robust one. We also consider the robustness of three-qubit pure states in correlated noisy channels. For the correlated bit flip and phase flip channels, the result shows that although the most robust and most fragile states are locally unitary equivalent, they exhibit different robustness in different correlated channels, and the effect of channel correlations on them is also significantly different. However, for the correlated depolarizing and bit-phase flip channels, the robustness of two special three-qubit pure states is exactly the same. Moreover, compared with the random three-qubit pure states, they are neither the most robust states nor the most fragile states.

Practical security analysis of continuous-variable quantum key distribution with an unbalanced heterodyne detector

Lingzhi Kong(孔令志), Weiqi Liu(刘维琪), Fan Jing(荆凡), and Chen He(贺晨)

Chin. Phys. B, 2022, 31 (7): 070303. DOI: 10.1088/1674-1056/ac4102

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When developing a practical continuous-variable quantum key distribution (CVQKD), the detector is necessary at the receiver's side. We investigate the practical security of the CVQKD system with an unbalanced heterodyne detector. The results show that unbalanced heterodyne detector introduces extra excess noise into the system and decreases the lower bound of the secret key rate without awareness of the legitimate communicators, which leaves loopholes for Eve to attack the system. In addition, we find that the secret key rate decreases more severely with the increase in the degree of imbalance and the excess noise induced by the imbalance is proportional to the intensity of the local oscillator (LO) under the same degree of imbalance. Finally, a countermeasure is proposed to resist these kinds of effects.

Photon blockade in a cavity-atom optomechanical system Suggested by editors

Zhong Ding(丁忠) and Yong Zhang(张勇)

Chin. Phys. B, 2022, 31 (7): 070304. DOI: 10.1088/1674-1056/ac4cbc

Abstract ( 317 )

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We study the single-photon blockade (1PB), two-photon blockade (2PB), and photon-induced tunneling (PIT) effects in a cavity-atom optomechanical system in which a two-level atom is coupled to a single-model cavity field via a two-photon interaction. By analyzing the eigenenergy spectrum of the system, we obtain a perfect 1PB with a high occupancy probability of single-photon excitation, which means that a high-quality and efficient single-photon source can be generated. However, PIT often occurs in many cases when we consider 2PB in analogy to 1PB. In addition, we find that a 2PB region will present in the optomechanical system, which can be proved by calculating the correlation function of the model analytically.

Anderson localization of a spin-orbit coupled Bose-Einstein condensate in disorder potential

Huan Zhang(张欢), Sheng Liu(刘胜), and Yongsheng Zhang(张永生)

Chin. Phys. B, 2022, 31 (7): 070305. DOI: 10.1088/1674-1056/ac538d

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We present numerical results of a one-dimensional spin-orbit coupled Bose-Einstein condensate expanding in a speckle disorder potential by employing the Gross-Pitaevskii equation. Localization properties of a spin-orbit coupled Bose-Einstein condensate in zero-momentum phase, magnetic phase and stripe phase are studied. It is found that the localizing behavior in the zero-momentum phase is similar to the normal Bose-Einstein condensate. Moreover, in both magnetic phase and stripe phase, the localization length changes non-monotonically as the fitting interval increases. In magnetic phases, the Bose-Einstein condensate will experience spin relaxation in disorder potential.

Gap solitons of spin-orbit-coupled Bose-Einstein condensates in $\mathcal{PT}$ periodic potential

S Wang(王双), Y H Liu(刘元慧), and T F Xu(徐天赋)

Chin. Phys. B, 2022, 31 (7): 070306. DOI: 10.1088/1674-1056/ac538e

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We numerically investigate the gap solitons in Bose-Einstein condensates (BECs) with spin-orbit coupling (SOC) in the parity-time ($\mathcal{PT}$)-symmetric periodic potential. We find that the depths and periods of the imaginary lattice have an important influence on the shape and stability of these single-peak gap solitons and double-peak gap solitons in the first band gap. The dynamics of these gap solitons are checked by the split-time-step Crank-Nicolson method. It is proved that the depths of the imaginary part of the $\mathcal{PT}$-symmetric periodic potential gradually increase, and the gap solitons become unstable. But the different periods of imaginary part hardly affect the stability of the gap solitons in the corresponding parameter interval.

Quantum speed limit of the double quantum dot in pure dephasing environment under measurement

Zhenyu Lin(林振宇), Tian Liu(刘天), Zongliang Li(李宗良), Yanhui Zhang(张延惠), and Kang Lan(蓝康)

Chin. Phys. B, 2022, 31 (7): 070307. DOI: 10.1088/1674-1056/ac4bd4

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The quantum speed limit (QSL) of the double quantum dot (DQD) system has been theoretically investigated by adopting the detection of the quantum point contact (QPC) in the pure dephasing environment. The Mandelstam-Tamm (MT) type of the QSL bound which is based on the trace distance has been extended to the DQD system for calculating the shortest evolving time. The increase of decoherence rate can weaken the capacity for potential speedup (CPS) and delay the evolving process due to the frequently measurement localizing the electron in the DQD system. The system needs longer time to evolve to the target state as the enhancement of dephasing rate, because the strong interaction between pure dephasing environment and the DQD system could vary the oscillation of the electron. Increasing the dephasing rate can sharp the QSL bound, but the decoherence rate would weaken the former effect and vice versa. Moreover, the CPS would be raised by increasing the energy displacement, while the enhancement of the coupling strength between two quantum dots can diminish it. It is interesting that there has an inflection point, when the coupling strength is less than the value of the point, the increasing effect of the CPS from the energy displacement is dominant, otherwise the decreasing tendency of the CPS is determined by the coupling strength and suppress the action of the energy displacement if the coupling strength is greater than the point. Our results provide theoretical reference for studying the QSL time in a semiconductor device affected by numerous factors.

Real non-Hermitian energy spectra without any symmetry

Boxue Zhang(张博学), Qingya Li(李青铔), Xiao Zhang(张笑), and Ching Hua Lee(李庆华)

Chin. Phys. B, 2022, 31 (7): 070308. DOI: 10.1088/1674-1056/ac67c6

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Non-Hermitian models with real eigenenergies are highly desirable for their stability. Yet, most of the currently known ones are constrained by symmetries such as PT-symmetry, which is incompatible with realizing some of the most exotic non-Hermitian phenomena. In this work, we investigate how the non-Hermitian skin effect provides an alternative route towards enforcing real spectra and system stability. We showcase, for different classes of energy dispersions, various ansatz models that possess large parameter space regions with real spectra, despite not having any obvious symmetry. These minimal local models can be quickly implemented in non-reciprocal experimental setups such as electrical circuits with operational amplifiers.

Kinetic theory of Jeans' gravitational instability in millicharged dark matter system Suggested by editors

Hui Chen(陈辉), Wei-Heng Yang(杨伟恒), Yu-Zhen Xiong(熊玉珍), and San-Qiu Liu(刘三秋)

Chin. Phys. B, 2022, 31 (7): 070401. DOI: 10.1088/1674-1056/ac5239

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The possibility of baryons cooled by a millicharged dark matter (mDM) via mDM-baryons scattering has recently been proposed to explain the observation discrepancy from the experiment to detect the global epoch of reionization signature (EDGES). In this sense, we analyze the Jeans instability of self-gravitational systems in the background of mDM under kinetic regime that the collisionless Boltzmann equation and Poisson equation have been combined to obtain the modified dispersion relation. It is shown that the effect of mDM is significant on the dynamics of gravitational collapse, i.e., the presence of mDM makes the self-gravitational systems more difficult to collapse relatively.

Data-driven modeling of a four-dimensional stochastic projectile system

Yong Huang(黄勇) and Yang Li(李扬)

Chin. Phys. B, 2022, 31 (7): 070501. DOI: 10.1088/1674-1056/ac4e0d

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The dynamical modeling of projectile systems with sufficient accuracy is of great difficulty due to high-dimensional space and various perturbations. With the rapid development of data science and scientific tools of measurement recently, there are numerous data-driven methods devoted to discovering governing laws from data. In this work, a data-driven method is employed to perform the modeling of the projectile based on the Kramers-Moyal formulas. More specifically, the four-dimensional projectile system is assumed as an Itô stochastic differential equation. Then the least square method and sparse learning are applied to identify the drift coefficient and diffusion matrix from sample path data, which agree well with the real system. The effectiveness of the data-driven method demonstrates that it will become a powerful tool in extracting governing equations and predicting complex dynamical behaviors of the projectile.

Universal order-parameter and quantum phase transition for two-dimensional q-state quantum Potts model

Yan-Wei Dai(代艳伟), Sheng-Hao Li(李生好), and Xi-Hao Chen(陈西浩)

Chin. Phys. B, 2022, 31 (7): 070502. DOI: 10.1088/1674-1056/ac4bd1

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We investigate quantum phase transitions for q-state quantum Potts models (q=2,3,4) on a square lattice and for the Ising model on a honeycomb lattice by using the infinite projected entangled-pair state algorithm with a simplified updating scheme. We extend the universal order parameter to a two-dimensional lattice system, which allows us to explore quantum phase transitions with symmetry-broken order for any translation-invariant quantum lattice system of the symmetry group G. The universal order parameter is zero in the symmetric phase, and it ranges from zero to unity in the symmetry-broken phase. The ground-state fidelity per lattice site is computed, and a pinch point is identified on the fidelity surface near the critical point. The results offer another example highlighting the connection between (i) critical points for a quantum many-body system undergoing a quantum phase-transition and (ii) pinch points on a fidelity surface. In addition, we discuss three quantum coherence measures: the quantum Jensen-Shannon divergence, the relative entropy of coherence, and the l₁ norm of coherence, which are singular at the critical point, thereby identifying quantum phase transitions.

Research and application of stochastic resonance in quad-stable potential system

Li-Fang He(贺利芳), Qiu-Ling Liu(刘秋玲), and Tian-Qi Zhang(张天骐)

Chin. Phys. B, 2022, 31 (7): 070503. DOI: 10.1088/1674-1056/ac4228

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To solve the problem of low weak signal enhancement performance in the quad-stable system, a new quad-stable potential stochastic resonance (QSR) is proposed. Firstly, under the condition of adiabatic approximation theory, the stationary probability distribution (SPD), the mean first passage time (MFPT), the work (W), and the power spectrum amplification factor (SAF) are derived, and the impacts of system parameters on them are also extensively analyzed. Secondly, numerical simulations are performed to compare QSR with the classical Tri-stable stochastic resonance (CTSR) by using the genetic algorithm (GA) and the fourth-order Runge-Kutta algorithm. It shows that the signal-to-noise ratio (SNR) and mean signal-to-noise increase (MSNRI) of QSR are higher than CTSR, which indicates that QSR has superior noise immunity than CTSR. Finally, the two systems are applied in the detection of real bearing faults. The experimental results show that QSR is superior to CTSR, which provides a better theoretical significance and reference value for practical engineering application.

Quantum search of many vertices on the joined complete graph

Tingting Ji(冀婷婷), Naiqiao Pan(潘乃桥), Tian Chen(陈天), and Xiangdong Zhang(张向东)

Chin. Phys. B, 2022, 31 (7): 070504. DOI: 10.1088/1674-1056/ac5241

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The quantum search on the graph is a very important topic. In this work, we develop a theoretic method on searching of single vertex on the graph [$Phys. Rev. Lett$. 114 110503 (2015)], and systematically study the search of many vertices on one low-connectivity graph, the joined complete graph. Our results reveal that, with the optimal jumping rate obtained from the theoretical method, we can find such target vertices at the time $O\left({\sqrt N } \right)$, where $N$ is the number of total vertices. Therefore, the search of many vertices on the joined complete graph possessing quantum advantage has been achieved.

Design and FPGA implementation of a memristor-based multi-scroll hyperchaotic system

Sheng-Hao Jia(贾生浩), Yu-Xia Li(李玉霞), Qing-Yu Shi(石擎宇), and Xia Huang(黄霞)

Chin. Phys. B, 2022, 31 (7): 070505. DOI: 10.1088/1674-1056/ac4a71

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A novel memristor-based multi-scroll hyperchaotic system is proposed. Based on a voltage-controlled memristor and a modulating sine nonlinear function, a novel method is proposed to generate the multi-scroll hyperchaotic attractors. Firstly, a multi-scroll chaotic system is constructed from a three-dimensional chaotic system by designing a modulating sine nonlinear function. Then, a voltage-controlled memristor is introduced into the above-designed multi-scroll chaotic system. Thus, a memristor-based multi-scroll hyperchaotic system is generated, and this hyperchaotic system can produce various coexisting hyperchaotic attractors with different topological structures. Moreover, different number of scrolls and different topological attractors can be obtained by varying the initial conditions of this system without changing the system parameters. The Lyapunov exponents, bifurcation diagrams and basins of attraction are given to analyze the dynamical characteristics of the multi-scroll hyperchaotic system. Besides, the field programmable gate array (FPGA) based digital implementation of the memristor-based multi-scroll hyperchaotic system is carried out. The experimental results of the FPGA-based digital circuit are displayed on the oscilloscope.

Negative self-feedback induced enhancement and transition of spiking activity for class-3 excitability

Li Li(黎丽), Zhiguo Zhao(赵志国), and Huaguang Gu(古华光)

Chin. Phys. B, 2022, 31 (7): 070506. DOI: 10.1088/1674-1056/ac4a63

Abstract ( 370 )

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Post-inhibitory rebound (PIR) spike, which has been widely observed in diverse nervous systems with different physiological functions and simulated in theoretical models with class-2 excitability, presents a counterintuitive nonlinear phenomenon in that the inhibitory effect can facilitate neural firing behavior. In this study, a PIR spike induced by inhibitory stimulation from the resting state corresponding to class-3 excitability that is not related to bifurcation is simulated in the Morris-Lecar neuron. Additionally, the inhibitory self-feedback mediated by an autapse with time delay can evoke tonic/repetitive spiking from phasic/transient spiking. The dynamical mechanism for the PIR spike and the tonic/repetitive spiking is acquired with the phase plane analysis and the shape of the quasi-separatrix curve. The result extends the counterintuitive phenomenon induced by inhibition to class-3 excitability, which presents a potential function of inhibitory autapse and class-3 neuron in many neuronal systems such as the auditory system.

Bifurcation analysis of visual angle model with anticipated time and stabilizing driving behavior

Xueyi Guan(管学义), Rongjun Cheng(程荣军), and Hongxia Ge(葛红霞)

Chin. Phys. B, 2022, 31 (7): 070507. DOI: 10.1088/1674-1056/ac5606

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In the light of the visual angle model (VAM), an improved car-following model considering driver's visual angle, anticipated time and stabilizing driving behavior is proposed so as to investigate how the driver's behavior factors affect the stability of the traffic flow. Based on the model, linear stability analysis is performed together with bifurcation analysis, whose corresponding stability condition is highly fit to the results of the linear analysis. Furthermore, the time-dependent Ginzburg-Landau (TDGL) equation and the modified Korteweg-de Vries (mKdV) equation are derived by nonlinear analysis, and we obtain the relationship of the two equations through the comparison. Finally, parameter calibration and numerical simulation are conducted to verify the validity of the theoretical analysis, whose results are highly consistent with the theoretical analysis.

Residual field suppression for magnetocardiography measurement inside a thin magnetically shielded room using bi-planar coil

Kang Yang(杨康), Hong-Wei Zhang(张宏伟), Qian-Nian Zhang(张千年),Jun-Jun Zha(查君君), and Deng-Chao Huang(黄登朝)

Chin. Phys. B, 2022, 31 (7): 070701. DOI: 10.1088/1674-1056/ac6163

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For a magnetocardiography (MCG) system inside a magnetically shielded room (MSR), the residual field should be further suppressed to obtain high-quality MCG signals. In this paper, a compensation system has been developed based on the bi-planar coil and the proportional-integral-derivative (PID) controller. The bi-planar coil, derived from the target-field theory and the Tikhonov regularization method, is utilized to generate magnetic field with high uniformity in the pre-defined target region. And the PID controller is introduced to provide dynamic compensation current for the coil, according to the residual field change monitored by a reference SQUID magnetometer. The measurement results show that the noise suppression ratio (NSR) can reach above 20 dB in the low-frequency range from 0.1 Hz to 50 Hz. The DC component and the fluctuation of the residual field in time-domain can be respectively suppressed to 0 pT and 4 pT, indicating that this proposed compensation method is useful for the MCG measurement.

Transient electromagnetically induced transparency spectroscopy of ⁸⁷Rb atoms in buffer gas

Zi-Shan Xu(徐子珊), Han-Mu Wang(王汉睦), Zeng-Li Ba(巴曾立), and Hong-Ping Liu(刘红平)

Chin. Phys. B, 2022, 31 (7): 073201. DOI: 10.1088/1674-1056/ac4748

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We study the transient response dynamics of ⁸⁷Rb atomic vapor buffered in 8 torr Ne gas through an electromagnetically induced transparency configured in $\varLambda$-scheme. Experimentally, the temporal transmission spectra versus probe detuning by switching on and off the coupling one show complex structures. The transmitted probe light intensity drops to a minimum value when the coupling light turns off, showing a strong absorption. Even at the moment of turning on the coupling light at a subsequent delayed time, the atomic medium shows a fast transient response. To account for the transient switching feature, in the time-dependent optical Bloch equation, we must take the transverse relaxation dephasing process of atomic vapor into account, as well as the fluorescence relaxation along with the optical absorption. This work supplies a technique to quantify the transverse relaxation time scale and to sensitively monitor its variation along the environment by observing the transient dynamics of coherent medium, which is helpful in characterizing the coherent feature of the atomic medium.

Electron emission induced by keV protons from tungsten surface at different temperatures

Li-Xia Zeng(曾利霞), Xian-Ming Zhou(周贤明), Rui Cheng(程锐), Yu Liu(柳钰), Xiao-An Zhang(张小安), and Zhong-Feng Xu(徐忠锋)

Chin. Phys. B, 2022, 31 (7): 073202. DOI: 10.1088/1674-1056/ac632f

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The electron emission yield is measured from the tungsten surface bombarded by the protons in an energy range of 50 keV-250 keV at different temperatures. In our experimental results, the total electron emission yield, which contains mainly the kinetic electron emission yield, has a very similar change trend to the electronic stopping power. At the same time, it is found that the ratio of total electron emission yield to electronic stopping power becomes smaller as the incident ion energy increases. The experimental result is explained by the ionization competition mechanism between electrons in different shells of the target atom. The explanation is verified by the opposite trends to the incident energy between the ionization cross section of M and outer shells.

Li(2p $\leftarrow$ 2s) + Na(3s) pressure broadening in the far-wing and line-core profiles

F Talbi, N Lamoudi, L Reggami, M T Bouazza, K Alioua, and M Bouledroua

Chin. Phys. B, 2022, 31 (7): 073401. DOI: 10.1088/1674-1056/ac43a0

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This work reports pressure-broadening line-wing and line-core of the lithium Li (2p $\leftarrow$ 2s) resonance line perturbed by ground sodium Na (3s) atoms. In far-wing regions, the calculations are performed quantum-mechanically and are intended to examine the photoabsorption coefficients at diverse temperatures. The results show the existence of three satellites, in the blue wing near the wavelengths 470 nm and in the red wing around 862 nm and 1070 nm. For the line-core region, by adopting the simplified Baranger model, the line-width and line-shift rates are determined, and their variation law with temperature is examined. No published data were found to compare these results with.

Development of an electronic stopping power model based on deep learning and its application in ion range prediction

Xun Guo(郭寻), Hao Wang(王浩), Changkai Li(李长楷),Shijun Zhao(赵仕俊), Ke Jin(靳柯), and Jianming Xue(薛建明)

Chin. Phys. B, 2022, 31 (7): 073402. DOI: 10.1088/1674-1056/ac4e0c

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Deep learning algorithm emerges as a new method to take the raw features from large dataset and mine their deep implicit relations, which is promising for solving traditional physical challenges. A particularly intricate and difficult challenge is the energy loss mechanism of energetic ions in solid, where accurate prediction of stopping power is a long-time problem. In this work, we develop a deep-learning-based stopping power model with high overall accuracy, and overcome the long-standing deficiency of the existing classical models by improving the predictive accuracy of stopping power for ultra-heavy ion with low energy, and the corresponding projected range. This electronic stopping power model, based on deep learning algorithm, could be hopefully applied for the study of ion-solid interaction mechanism and enormous relevant applications.

Enhanced cold mercury atom production with two-dimensional magneto-optical trap

Ye Zhang(张晔), Qi-Xin Liu(刘琪鑫), Jian-Fang Sun(孙剑芳), Zhen Xu(徐震), and Yu-Zhu Wang(王育竹)

Chin. Phys. B, 2022, 31 (7): 073701. DOI: 10.1088/1674-1056/ac5397

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A cold atom source is important for quantum metrology and precision measurement. To reduce the quantum projection noise limit in optical lattice clock, one can increase the number of cold atoms and reduce the dead time by enhancing the loading rate. In this work, we realize an enhanced cold mercury atom source based on a two-dimensional (2D) magneto-optical trap (MOT). The vacuum system is composed of two titanium chambers connected with a differential pumping tube. Two stable cooling laser systems are adopted for the 2D-MOT and the three-dimensional (3D)-MOT, respectively. Using an optimized 2D-MOT and push beam, about 1.3×10⁶ atoms, which are almost an order of magnitude higher than using a pure 3D-MOT, are loaded into the 3D-MOT for ²⁰²Hg atoms. This enhanced cold mercury atom source is helpful in increasing the frequency stability of a neutral mercury lattice clock.

Superfluid to Mott-insulator transition in a one-dimensional optical lattice Suggested by editors

Wenliang Liu(刘文良), Ningxuan Zheng(郑宁宣), Jun Jian(蹇君), Li Tian(田丽), Jizhou Wu(武寄洲), Yuqing Li(李玉清), Yongming Fu(付永明), Peng Li(李鹏), Vladimir Sovkov, Jie Ma(马杰), Liantuan Xiao(肖连团), and Suotang Jia(贾锁堂)

Chin. Phys. B, 2022, 31 (7): 073702. DOI: 10.1088/1674-1056/ac6579

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Bose-Einstein condensates (BEC) of sodium atoms are transferred into one-dimensional (1D) optical lattice potentials, formed by two laser beams with a wavelength of 1064 nm, in a shallow optical trap. The phase coherence of the condensate in the lattice potential is studied by changing the lattice depth. A qualitative change in behavior of the BEC is observed at a lattice depth of ～ 13.7 E_r, where the quantum gas undergoes a transition from a superfluid state to a state that lacks well-to-well phase coherence.

Goos-Hänchen and Imbert-Fedorov shifts in tilted Weyl semimetals

Shuo-Qing Liu(刘硕卿), Yi-Fei Song(宋益飞), Ting Wan(万婷), You-Gang Ke(柯友刚), and Zhao-Ming Luo(罗朝明)

Chin. Phys. B, 2022, 31 (7): 074101. DOI: 10.1088/1674-1056/ac4e03

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We establish the beam models of Goos-Hänchen (GH) and Imbert-Fedorov (IF) effects in tilted Weyl semimetals (WSMs), and systematically study the influences of Weyl cone tilting and chemical potential on the GH and IF shifts at a certain photon energy 1.96 eV. It is found that the GH and IF shifts in tilted type-I and type-Ⅱ WSMs are both almost symmetric about the Weyl cone tilting. Meanwhile, the GH and IF shifts in type-I WSMs almost do not change with the tilt degree of Weyl cones, while those in type-Ⅱ WSMs are extremely dependent on tilt degree. These trends are mainly due to the nearly symmetric distribution of WSMs conductivities, where the conductivities keep stable in type-I WSMs and gradually decrease with tilt degree in type-Ⅱ WSMs. By adjusting the chemical potential, the boundary between type-I and type-Ⅱ WSMs widens, and the dependence of the beam shifts on the tilt degree can be manipulated. Furthermore, by extending the relevant discussions to a wider frequency band, the peak fluctuation of GH shifts and the decrease of IF shifts occur gradually as the frequency increases, and the performance of beam shifts at photon energy 1.96 eV is equally suitable for other photon frequencies. The above findings provide a new reference for revisiting the beam shifts in tilted WSMs and determining the types of WSMs.

Design of three-dimensional imaging lidar optical system for large field of view scanning

Qing-Yan Li(李青岩), Yu Zhang(张雨), Shi-Yu Yan(闫诗雨),Bin Zhang(张斌), and Chun-Hui Wang(王春晖)

Chin. Phys. B, 2022, 31 (7): 074201. DOI: 10.1088/1674-1056/ac4a67

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Three-dimensional (3D) lidar has been widely used in various fields. The MEMS scanning system is one of its most important components, while the limitation of scanning angle is the main obstacle to improve the demerit for its application in various fields. In this paper, a folded large field of view scanning optical system is proposed. The structure and parameters of the system are determined by theoretical derivation of ray tracing. The optical design software Zemax is used to design the system. After optimization, the final structure performs well in collimation and beam expansion. The results show that the scan angle can be expanded from ±5° to ±26.5°, and finally the parallel light scanning is realized. The spot diagram at a distance of 100 mm from the exit surface shows that the maximum radius of the spot is 0.506 mm with a uniformly distributed spot. The maximum radius of the spot at 100 m is 19 cm, and the diffusion angle is less than 2 mrad. The energy concentration in the spot range is greater than 90% with a high system energy concentration, and the parallelism is good. This design overcomes the shortcoming of the small mechanical scanning angle of the MEMS lidar, and has good performance in collimation and beam expansion. It provides a design method for large-scale application of MEMS lidar.

Reflection and transmission of an Airy beam in a dielectric slab

Xiaojin Yang(杨小锦), Tan Qu(屈檀), Zhensen Wu(吴振森), Haiying Li(李海英), Lu Bai(白璐), Lei Gong(巩蕾), and Zhengjun Li(李正军)

Chin. Phys. B, 2022, 31 (7): 074202. DOI: 10.1088/1674-1056/ac4e07

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The reflection and transmission of a finite-power Airy beam incident on a dielectric slab are investigated by an analytical method. Based on the plane-wave angular spectrum expansion and Fresnel approximation, the analytical expressions of the reflected field, internal field as well as transmitted field in each region are obtained. Through numerical simulations, the intensity distributions of the incident beam, reflected beam, internal beam as well as transmitted beam are presented at oblique incidence. Besides, we also compare the intensity distributions of the geometrical-optics beam field, the first order beam mode field and the actual beam field, which indicates that the contribution of each order beam mode field to the actual beam field is related to the refractive index of the dielectric slab. Meanwhile, the reflection characteristics of the Airy beams in the special cases of Brewster incidence and total reflection are investigated. Finally, the effects of the optical thickness and refractive index of the dielectric slab on the peak intensity distributions and beam shifts of the reflected and transmitted beams are also discussed in detail. The analytical and numerical results will be useful to analyze the propagation dynamics of Airy beam in the dielectric slab and provide some theoretical supports to the design of optical film.

A novel demodulation method for transmission using nitrogen-vacancy-based solid-state quantum sensor Suggested by editors

Ruixin Bai(白瑞昕), Xinyue Zhu(朱欣岳), Fan Yang(杨帆), Tianran Gao(高天然), Ziran Wang(汪子然), Linyan Yu(虞林嫣), Jinfeng Wang(汪晋锋), Li Zhou(周力), and Guanxiang Du(杜关祥)

Chin. Phys. B, 2022, 31 (7): 074203. DOI: 10.1088/1674-1056/ac5618

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Diamond based quantum sensing is a fast-emerging field with both scientific and technological significance. The nitrogen-vacancy (NV) center, a crystal defect in diamond, has become a unique object for microwave sensing applications due to its excellent stability, long spin coherence time, and optical properties at ambient condition. In this work, we use diamond NV center as atomic receiver to demodulate on-off keying (OOK) signal transmitted in broad frequency range (2 GHz-14 GHz in a portable benchtop setup). We proposed a unique algorithm of voltage discrimination and demonstrated audio signal transceiving with fidelity above 99%. This diamond receiver is attached to the end of a tapered fiber, having all optic nature, which will find important applications in data transmission tasks under extreme conditions such as strong electromagnetic interference, high temperatures, and high corrosion.

Manipulation of nonreciprocal unconventional photon blockade in a cavity-driven system composed of an asymmetrical cavity and two atoms with weak dipole-dipole interaction

Xinqin Zhang(张新琴), Xiuwen Xia(夏秀文), Jingping Xu(许静平), Haozhen Li(李浩珍), Zeyun Fu(傅泽云), and Yaping Yang(羊亚平)

Chin. Phys. B, 2022, 31 (7): 074204. DOI: 10.1088/1674-1056/ac523f

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We present a work of manipulating collective unconventional photon blockade (UCPB) and nonreciprocal UCPB (NUCPB) in a cavity-driven system composed of an asymmetrical single-mode cavity and two interacting identical two-level atoms (TLAs). When the atoms do not interact directly, the frequency and intensity restrictions of collective UCPB can be specified, and a giant NUCPB exists due to the splitting of optimal atom-cavity coupling strength in proper parameter regime. However, if a weak atom-atom interaction which provides a new and feeble quantum interference pathway to UCPB is taken into account, two restrictions of UCPB are combined complexly, which are rigorous to be matched simultaneously. Due to the push-and-pull effect induced by weak dipole-dipole interaction, the UCPB regime is compressed more or less. NUCPB is improved as a higher contrast is present when the two complex UCPB restrictions are matched, while it is suppressed when the restrictions are mismatched. In general, whether NUCPB is suppressed or promoted depends on its working parameters. Our findings show a prospective access to produce giant quantum nonreciprocity by a couple of weakly interacting atoms.

Multi-target ranging using an optical reservoir computing approach in the laterally coupled semiconductor lasers with self-feedback

Dong-Zhou Zhong(钟东洲), Zhe Xu(徐喆), Ya-Lan Hu(胡亚兰), Ke-Ke Zhao(赵可可), Jin-Bo Zhang(张金波),Peng Hou(侯鹏), Wan-An Deng(邓万安), and Jiang-Tao Xi(习江涛)

Chin. Phys. B, 2022, 31 (7): 074205. DOI: 10.1088/1674-1056/ac4021

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We utilize three parallel reservoir computers using semiconductor lasers with optical feedback and light injection to model radar probe signals with delays. Three radar probe signals are generated by driving lasers constructed by a three-element laser array with self-feedback. The response lasers are implemented also by a three-element lase array with both delay-time feedback and optical injection, which are utilized as nonlinear nodes to realize the reservoirs. We show that each delayed radar probe signal can be predicted well and to synchronize with its corresponding trained reservoir, even when parameter mismatches exist between the response laser array and the driving laser array. Based on this, the three synchronous probe signals are utilized for ranging to three targets, respectively, using Hilbert transform. It is demonstrated that the relative errors for ranging can be very small and less than 0.6%. Our findings show that optical reservoir computing provides an effective way for applications of target ranging.

Enhancing performance of GaN-based LDs by using GaN/InGaN asymmetric lower waveguide layers

Wen-Jie Wang(王文杰), Ming-Le Liao(廖明乐), Jun Yuan(袁浚), Si-Yuan Luo(罗思源), and Feng Huang(黄锋)

Chin. Phys. B, 2022, 31 (7): 074206. DOI: 10.1088/1674-1056/ac597c

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The effects of GaN/InGaN asymmetric lower waveguide (LWG) layers on photoelectrical properties of InGaN multiple quantum well laser diodes (LDs) with an emission wavelength of around 416 nm are theoretically investigated by tuning the thickness and the indium content of InGaN insertion layer (InGaN-IL) between the GaN lower waveguide layer and the quantum wells, which is achieved with the Crosslight Device Simulation Software (PIC3D, Crosslight Software Inc.). The optimal thickness and the indium content of the InGaN-IL in lower waveguide layers are found to be 300 nm and 4%, respectively. The thickness of InGaN-IL predominantly affects the output power and the optical field distribution in comparison with the indium content, and the highest output power is achieved to be 1.25 times that of the reference structure (symmetric GaN waveguide), which is attributed to the reduced optical absorption loss as well as the concentrated optical field nearby quantum wells. Furthermore, when the thickness and indium content of InGaN-IL both reach a higher level, the performance of asymmetric quantum wells LDs will be weakened rapidly due to the obvious decrease of optical confinement factor (OCF) related to the concentrated optical field in the lower waveguide.

Precise determination of characteristic laser frequencies by an Er-doped fiber optical frequency comb Suggested by editors

Shiying Cao(曹士英), Yi Han(韩羿), Yongjin Ding(丁永今), Baike Lin(林百科), and Zhanjun Fang(方占军)

Chin. Phys. B, 2022, 31 (7): 074207. DOI: 10.1088/1674-1056/ac5608

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Femtosecond optical frequency combs correlate the microwave and optical frequencies accurately and coherently. Therefore, any optical frequency in visible to near-infrared region can be directly traced to a microwave frequency. As a result, the length unit "meter" is directly related to the time unit "second". This paper validates the capability of the national wavelength standards based on a home-made Er-doped fiber femtosecond optical frequency comb to measure the laser frequencies ranging from visible to near-infrared region. Optical frequency conversion in the femtosecond optical frequency comb is achieved by combining spectral broadening in a highly nonlinear fiber with a single-point frequency-doubling scheme. The signal-to-noise ratio of the beat notes between the femtosecond optical frequency comb and the lasers at 633, 698, 729, 780, 1064, and 1542 nm is better than 30 dB. The frequency instability of the above lasers is evaluated by using a hydrogen clock signal with a instability of better than 1×10^-13 at 1-s averaging time. The measurement is further validated by measuring the absolute optical frequency of an iodine-stabilized 532-nm laser and an acetylene-stabilized 1542-nm laser. The results are within the uncertainty range of the international recommended values. Our results demonstrate the accurate optical frequency measurement of lasers at different frequencies using the femtosecond optical frequency comb, which is not only important for the precise and accurate traceability and calibration of the laser frequencies, but also provides technical support for establishing the national wavelength standards based on the femtosecond optical frequency comb.

Spatio-spectral dynamics of soliton pulsation with breathing behavior in the anomalous dispersion fiber laser

Ying Han(韩颖), Bo Gao(高博), Jiayu Huo(霍佳雨), Chunyang Ma(马春阳), Ge Wu(吴戈),Yingying Li(李莹莹), Bingkun Chen(陈炳焜), Yubin Guo(郭玉彬), and Lie Liu(刘列)

Chin. Phys. B, 2022, 31 (7): 074208. DOI: 10.1088/1674-1056/ac4023

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We have numerically and experimentally observed the soliton pulsation with obvious breathing behavior in the anomalous fiber laser mode-locked by a nonlinear polarization rotation technique. The numerical study of the soliton pulsation with breathing behavior was analyzed through the split-step Fourier method at first, and it was found that the phase difference caused by the polarization controller would affect the breathing characteristics. Then, taking advantage of the dispersive Fourier transform technique, we confirmed the breathing characteristic of soliton pulsation in the same fiber laser as the simulation model experimentally. These results complement the research on the breathing characteristic of soliton pulsation.

THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves

Zhongyang Li(李忠洋), Qianze Yan(颜钤泽), Pengxiang Liu(刘鹏翔), Binzhe Jiao(焦彬哲), Gege Zhang(张格格), Zhiliang Chen(陈治良), Pibin Bing(邴丕彬), Sheng Yuan(袁胜), Kai Zhong(钟凯), and Jianquan Yao(姚建铨)

Chin. Phys. B, 2022, 31 (7): 074209. DOI: 10.1088/1674-1056/ac5243

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We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves (HSWs). The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity (RC) where low-order Stokes waves (LSWs) are converted to high-order Stokes waves again and again. The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation (OCDFG) where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally. Combined with the repeated and continuous frequency conversions, the optical-to-THz energy conversion efficiency (OTECE) exceeds 26% at 300 K and 43% at 100 K with pump intensities of 300 MW/cm².

Large aperture phase-coded diffractive lens for achromatic and 16° field-of-view imaging with high efficiency

Gu Ma(马顾), Peng-Lei Zheng(郑鹏磊), Zheng-Wen Hu(胡正文), Suo-Dong Ma(马锁冬), Feng Xu(许峰), Dong-Lin Pu(浦东林), and Qin-Hua Wang(王钦华)

Chin. Phys. B, 2022, 31 (7): 074210. DOI: 10.1088/1674-1056/ac560c

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Diffractive lenses (DLs) can realize high-resolution imaging with light weight and compact size. Conventional DLs suffer large chromatic and off-axis aberrations, which significantly limits their practical applications. Although many achromatic methods have been proposed, most of them are used for designing small aperture DLs, which have low diffraction efficiencies. In the designing of diffractive achromatic lenses, increasing the aperture and improving the diffraction efficiency have become two of the most important design issues. Here, a novel phase-coded diffractive lens (PCDL) for achromatic imaging with a large aperture and high efficiency is proposed and demonstrated experimentally, and it also possesses wide field-of-view (FOV) imaging at the same time. The phase distribution of the conventional phase-type diffractive lens (DL) is coded with a cubic function to expand both the working bandwidth and the FOV of conventional DL. The proposed phase-type DL is fabricated by using the laser direct writing of grey-scale patterns for a PCDL of a diameter of 10 mm, a focal length of 100 mm, and a cubic phase coding parameter of 30π. Experimental results show that the working bandwidth and the FOV of the PCDL respectively reach 50 nm and 16° with over 8% focusing efficiency, which are in significant contrast to the counterparts of conventional DL and in good agreement with the theoretical predictions. This work provides a novel way for implementing the achromatic, wide FOV, and high-efficiency imaging with large aperture DL.

A radiation-temperature coupling model of the optical fiber attenuation spectrum in the Ge/P co-doped fiber

Yong Li(李勇), Haoshi Zhang(张浩石), Xiaowei Wang(王晓伟), and Jing Jin(金靖)

Chin. Phys. B, 2022, 31 (7): 074211. DOI: 10.1088/1674-1056/ac40f9

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A radiation-temperature coupling model of optical fiber attenuation spectrum has been developed. The spectrum in Ge/P co-doped fiber ranging from 800 nm-1600 nm at different temperatures and doses was measured and decomposed according to the configurational coordinate model based on which the power-law model was employed to predict the intensity of the color center absorption band at different doses. And the fiber loss in space was predicted by the model. This work will benefit the application of fibers in a complicated radiation environment.

Design of an all-dielectric long-wave infrared wide-angle metalens

Ning Zhang(张宁), Qingzhi Li(李青芝), Jun Chen(陈骏), Feng Tang(唐烽),Jingjun Wu(伍景军), Xin Ye(叶鑫), and Liming Yang(杨李茗)

Chin. Phys. B, 2022, 31 (7): 074212. DOI: 10.1088/1674-1056/ac4026

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Optical metasurfaces are two-dimensional arrays of nano-scatterers that modify optical wavefronts at subwavelength spatial resolution. They achieve the effect of focusing through phase control under a subwavelength scale, and are called metalenses. They are poised to revolutionize optics by enabling complex low-cost systems. However, there are severe monochromatic aberrations in the metasurfaces. In this paper, the coma of the long-wave infrared optical system is eliminated through a single-layer metasurface. By changing the phase function, this metalens has a numerical aperture of 0.89, a focal length of 150 μm and a field of view of 120° (0.4@60 line pairs/mm) that enables diffraction-limited monochromatic imaging along the focal plane at a wavelength of 10.6 μm. The designed metasurface maintains a favorable value of the modulation transfer function at different angles. This equipment can be widely used in imaging and industrial processing.

Nonlinear inversion of ultrasonic guided waves for in vivo evaluation of cortical bone properties

Xiaojun Song(宋小军), Tiandi Fan(樊天地), Jundong Zeng(曾俊冬), Qin-Zhen Shi(石勤振), Qiong Huang(黄琼), Meilin Gu(顾美琳), Petro Moilanen, Yi-Fang Li(李义方), and Dean Ta(他得安)

Chin. Phys. B, 2022, 31 (7): 074301. DOI: 10.1088/1674-1056/ac3eca

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Ultrasonic guided waves (UGWs), which propagate throughout the entire thickness of cortical bone, are attractive for the early diagnosis of osteoporosis. However, this is challenging due to the impact of soft tissue and the inherent difficulties related to multiparametric inversion of cortical bone quality factors, such as cortical thickness and bulk wave velocity. Therefore, in this research, a UGW-based multi-parameter inversion algorithm is developed to predict strength-related factors. In simulation, a free plate (cortical bone) and a bilayer plate (soft tissue and cortical bone) are used to validate the proposed method. The inversed cortical thickness (CTh), longitudinal velocity (V_L) and transverse velocity (V_T) are in accordance with the true values. Then four bovine cortical bone plates were used in in vitro experiments. Compared with the reference values, the relative errors for cortical thickness were 3.96%, 0.83%, 2.87%, and 4.25%, respectively. In the in vivo measurements, UGWs are collected from the tibias of 10 volunteers. The theoretical dispersion curves depicted by the estimated parameters (V_T, V_L, CTh) match well with the extracted experimental ones. In comparison with dual-energy x-ray absorptiometry, our results show that the estimated transverse velocity and cortical thickness are highly sensitive to osteoporosis. Therefore, these two parameters (CTh and V_T) of long bones have potential to be used for diagnosis of bone status in clinical applications.

Effects of single synthetic jet on turbulent boundary layer

Jin-Hao Zhang(张津浩), Biao-Hui Li(李彪辉), Yu-Fei Wang(王宇飞), and Nan Jiang(姜楠)

Chin. Phys. B, 2022, 31 (7): 074702. DOI: 10.1088/1674-1056/ac4bd0

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The turbulent boundary layer (TBL) is actively controlled by the synthetic jet generated from a circular hole. According to the datasets of velocity fields acquired by a time-resolved particle image velocimetry (TR-PIV) system, the average drag reduction rate of 6.2% in the downstream direction of the hole is obtained with control. The results of phase averaging show that the synthetic jet generates one vortex pair each period and the consequent vortex evolves into hairpin vortex in the environment with free-stream, while the reverse vortex decays rapidly. From the statistical average, it can be found that a low-speed streak is generated downstream. Induced by the two vortex legs, the fluid under them converges to the middle. The drag reduction effect produced by the synthetic jet is local, and it reaches a maximum value at x⁺=400, where the drag reduction rate reaches about 12.2%. After the extraction of coherent structure from the spatial two-point correlation analysis, it can be seen that the synthetic jet suppresses the streamwise scale and wall-normal scale of the large scale coherent structure, and slightly weakens the spanwise motion to achieve the effect of drag reduction.

Modeling of beam ions loss and slowing down with Coulomb collisions in EAST Suggested by editors

Yifeng Zheng(郑艺峰), Jianyuan Xiao(肖建元), Baolong Hao(郝保龙), Liqing Xu(徐立清), Yanpeng Wang(王彦鹏), Jiangshan Zheng(郑江山), and Ge Zhuang(庄革)

Chin. Phys. B, 2022, 31 (7): 075201. DOI: 10.1088/1674-1056/ac5883

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This paper uses the implicit Monte-Carlo full-orbit-following parallel program ISSDE to calculate the prompt loss and slowing down process of neutral beam injection (NBI)-generated fast ions due to Coulomb collisions in the equilibrium configuration of Experimental Advanced Superconducting Tokamak (EAST). This program is based on the weak equivalence of the Fokker-Planck equation under Rosenbluth MacDonald Judd (RMJ) potential and Stratonovich stochastic differential equation (SDE). The prompt loss with the LCFS boundary and the first wall (FW) boundary of the two co-current neutral injection beams are studied. Simulation results indicate that the loss behavior of fast ions using the FW boundary is very different from that of the LCFS boundary, especially for fast ions with a large gyration radius. According to our calculations, about 5.11% of fast ions generated by perpendicular injection drift out of the LCFS and then return inside the LCFS to be captured by the magnetic field. The prompt loss ratio of fast ions and the ratio of orbital types depend on the initial distribution of fast ions in the P_ζ-$\varLambda$ space. Under the effect of Coulomb collisions, the pitch-angle scattering and stochastic diffusion happens, which will cause more fast ion loss. For short time scales, among the particles lost due to collisions, the fraction of banana ions reaches 92.31% in the perpendicular beam and 58.65% in the tangential beam when the fraction of banana ions in the tangential beam is 3.4% of the total ions, which means that the effect of Coulomb collisions on banana fast ions is more significant. For long time scales, the additional fast ion loss caused by Coulomb collisions of tangential and perpendicular beams accounted for 16.21% and 25.05% of the total particles, respectively. We have also investigated the slowing down process of NBI fast ions.

Interaction between plasma and electromagnetic field in ion source of 10 cm ECR ion thruster

Hao Mou(牟浩), Yi-Zhou Jin(金逸舟), Juan Yang(杨涓), Xu Xia(夏旭), and Yu-Liang Fu(付瑜亮)

Chin. Phys. B, 2022, 31 (7): 075202. DOI: 10.1088/1674-1056/ac4906

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Through diagnosing the plasma density and calculating the intensity of microwave electric field, four 10 cm electron cyclotron resonance (ECR) ion sources with different magnetic field structures are studied to reveal the inside interaction between the plasma, magnetic field and microwave electric field. From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with the magnetic field and microwave power level. Based on the cold plasma hypothesis and diagnosing result, the microwave electric field intensity distribution in the plasma is calculated. The result shows that the plasma will significantly change the distribution of the microwave electric field intensity to form a bow shape. From the boundary region of the shape to the center, the electric field intensity varies from higher to lower and the diagnosed density inversely changes. If the bow and its inside lower electric field intensity region are close to the screen grid, the performance of ion beam extracting will be better. The study can provide useful information for the creating of 10 cm ECR ion source and understanding its mechanism.

Plasma-wave interaction in helicon plasmas near the lower hybrid frequency

Yide Zhao(赵以德), Jinwei Bai(白进纬), Yong Cao(曹勇), Siyu Wu(吴思宇), Eduardo Ahedo, Mario Merino, and Bin Tian(田滨)

Chin. Phys. B, 2022, 31 (7): 075203. DOI: 10.1088/1674-1056/ac40fd

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We study the characteristics of plasma-wave interaction in helicon plasmas near the lower hybrid frequency. The (0D) dispersion relation is derived to analyze the properties of the wave propagation and a 1D cylindrical plasma-wave interaction model is established to investigate the power deposition and to implement the parametric analysis. It is concluded that the lower hybrid resonance is the main mechanism of the power deposition in helicon plasmas when the RF frequency is near the lower hybrid frequency and the power deposition mainly concentrates on a very thin layer near the boundary. Therefore, it causes that the plasma resistance has a large local peak near the lower hybrid frequency and the variation of the plasma density and the parallel wavenumber lead to the frequency shifting of the local peaks. It is found that the magnetic field is still proportional to the plasma density for the local maximum plasma resistance and the slope changes due to the transition.

Numerical simulation of fueling pellet ablation and transport in the EAST H-mode discharge

Wan-Ting Chen(陈婉婷), Ji-Zhong Sun(孙继忠), Fang Gao(高放), Lei Peng(彭磊), and De-Zhen Wang(王德真)

Chin. Phys. B, 2022, 31 (7): 075204. DOI: 10.1088/1674-1056/ac5c35

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To understand the effect of injected deuterium (D) pellets on background plasma, the ablation of D pellets and the transport of D species in both atomic and ionic states in the EAST device are simulated using a modified dynamic neutral gas shield model combined with the edge plasma code SOLPS-ITER. The simulation results show that there is a phenomenon of obvious atomic deposition in the scrape-off layer (SOL) after pellet injection, which depends strongly on the injection velocity. With increasing injection velocity, the atomic density in the SOL decreases evidently and the deposition time is relatively shortened. Possible effects for triggering of edge localized modes (ELMs) by D and Li pellets are also discussed. With the same pellet size and injection velocity, the maximum perturbation pressure caused by D pellets is obviously higher. It is found that the resulting maximum perturbed pressure is remarkably enhanced when the injection velocity is reduced from 300 m/s to 100 m/s for a pellet with a cross section of 1.6 mm, which indicates that the injection velocity is important for ELM pacing. This work can provide reasonable guidance for choosing pellet parameters for fueling and ELM triggering.

Structural evolution and bandgap modulation of layered β-GeSe₂ single crystal under high pressure ^Hot!

Hengli Xie(谢恒立), Jiaxiang Wang(王家祥), Lingrui Wang(王玲瑞), Yong Yan(闫勇), Juan Guo(郭娟), Qilong Gao(高其龙), Mingju Chao(晁明举), Erjun Liang(梁二军), and Xiao Ren(任霄)

Chin. Phys. B, 2022, 31 (7): 076101. DOI: 10.1088/1674-1056/ac6db8

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Germanium diselenide (GeSe₂) is a promising candidate for electronic devices because of its unique crystal structure and optoelectronic properties. However, the evolution of lattice and electronic structure of $β$-GeSe₂ at high pressure is still uncertain. Here we prepared high-quality $β$-GeSe₂ single crystals by chemical vapor transfer (CVT) technique and performed systematic experimental studies on the evolution of lattice structure and bandgap of $β$-GeSe₂ under pressure. High-precision high-pressure ultra low frequency (ULF) Raman scattering and synchrotron angle-dispersive x-ray diffraction (ADXRD) measurements support that no structural phase transition exists under high pressure up to 13.80 GPa, but the structure of $β$-GeSe₂ turns into a disordered state near 6.91 GPa and gradually becomes amorphous forming an irreversibly amorphous crystal at 13.80 GPa. Two Raman modes keep softening abnormally upon pressure. The bandgap of $β$-GeSe₂ reduced linearly from 2.59 eV to 1.65 eV under pressure with a detectable narrowing of 36.5%, and the sample under pressure performs the piezochromism phenomenon. The bandgap after decompression is smaller than that in the atmospheric pressure environment, which is caused by incomplete recrystallization. These results enrich the insight into the structural and optical properties of $β$-GeSe₂ and demonstrate the potential of pressure in modulating the material properties of two-dimensional (2D) Ge-based binary material.

Structural evolution and molecular dissociation of H₂S under high pressures

Wen-Ji Shen(沈文吉), Tian-Xiao Liang(梁天笑), Zhao Liu(刘召), Xin Wang(王鑫), De-Fang Duan(段德芳), Hong-Yu Yu(于洪雨), and Tian Cui(崔田)

Chin. Phys. B, 2022, 31 (7): 076102. DOI: 10.1088/1674-1056/ac5980

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Solid H$_{2}$S as the precursor for H$_{3}$S with incredible superconducting properties under high pressure, has recently attracted extensive attention. Here in this work, we propose two new phases of H$_{2}$S with $P$4$_{2}/n$ and $I$4$_{1}/a$ lattice symmetries in a pressure range of 0 GPa-30 GPa through first-principles structural searches, which complement the phase transition sequence. Further an $ab initio$ molecular dynamics simulation confirms that the molecular phase $P2/c$ of H$_{2}$S is gradually dissociated with the pressure increasing and reconstructs into a new $P$2$_{1}/m$ structure at 160 GPa, exhibiting the superconductivity with $T_{\rm c}$ of 82.5 K. Our results may provide a guidance for the theoretical study of low-temperature superconducting phase of H$_{2}$S.

Heterogeneous integration of GaSb layer on (100) Si substrate by ion-slicing technique

Ren-Jie Liu(刘仁杰), Jia-Jie Lin(林家杰), Zheng-Hao Shen(沈正皓), Jia-Liang Sun(孙嘉良), Tian-Gui You(游天桂), Jin Li(李进), Min Liao(廖敏), and Yi-Chun Zhou(周益春)

Chin. Phys. B, 2022, 31 (7): 076103. DOI: 10.1088/1674-1056/ac5605

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Integration of the high-quality GaSb layer on an Si substrate is significant to improve the GaSb application in optoelectronic integration. In this work, a suitable ion implantation fluence of 5×10¹⁶-cm^-2 H ions for GaSb layer transfer is confirmed. Combining the strain change and the defect evolution, the blistering and exfoliation processes of GaSb during annealing is revealed in detail. With the direct wafer bonding, the GaSb layer is successfully transferred onto a (100) Si substrate covered by 500-nm thickness thermal oxide SiO₂ layer. After being annealed at 200 ℃, the GaSb layer shows high crystalline quality with only 77 arcsec for the full width at half maximum (FWHM) of the x-ray rocking curve (XRC).

Introducing voids around the interlayer of AlN by high temperature annealing

Jianwei Ben(贲建伟), Jiangliu Luo(罗江流), Zhichen Lin(林之晨), Xiaojuan Sun(孙晓娟), Xinke Liu(刘新科), and Xiaohua Li(黎晓华)

Chin. Phys. B, 2022, 31 (7): 076104. DOI: 10.1088/1674-1056/ac3d7f

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Introducing voids into AlN layer at a certain height using a simple method is meaningful but challenging. In this work, the AlN/sapphire template with AlN interlayer structure was designed and grown by metal-organic chemical vapor deposition. Then, the AlN template was annealed at 1700 ℃ for an hour to introduce the voids. It was found that voids were formed in the AlN layer after high-temperature annealing and they were mainly distributed around the AlN interlayer. Meanwhile, the dislocation density of the AlN template decreased from 5.26×10⁹ cm^-2 to 5.10×10⁸ cm^-2. This work provides a possible method to introduce voids into AlN layer at a designated height, which will benefit the design of AlN-based devices.

Direct visualization of structural defects in 2D semiconductors ^Hot!

Yutuo Guo(郭玉拓), Qinqin Wang(王琴琴), Xiaomei Li(李晓梅), Zheng Wei(魏争), Lu Li(李璐), Yalin Peng(彭雅琳), Wei Yang(杨威), Rong Yang(杨蓉), Dongxia Shi(时东霞), Xuedong Bai(白雪冬), Luojun Du(杜罗军), and Guangyu Zhang(张广宇)

Chin. Phys. B, 2022, 31 (7): 076105. DOI: 10.1088/1674-1056/ac6738

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Direct visualization of the structural defects in two-dimensional (2D) semiconductors at a large scale plays a significant role in understanding their electrical/optical/magnetic properties, but is challenging. Although traditional atomic resolution imaging techniques, such as transmission electron microscopy and scanning tunneling microscopy, can directly image the structural defects, they provide only local-scale information and require complex setups. Here, we develop a simple, non-invasive wet etching method to directly visualize the structural defects in 2D semiconductors at a large scale, including both point defects and grain boundaries. Utilizing this method, we extract successfully the defects density in several different types of monolayer molybdenum disulfide samples, providing key insights into the device functions. Furthermore, the etching method we developed is anisotropic and tunable, opening up opportunities to obtain exotic edge states on demand.

Onion-structured transition metal dichalcogenide nanoparticles by laser fabrication in liquids and atmospheres

Le Zhou(周乐), Hongwen Zhang(张洪文), Qian Zhao(赵倩), and Weiping Cai(蔡伟平)

Chin. Phys. B, 2022, 31 (7): 076106. DOI: 10.1088/1674-1056/ac539c

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Since the discovery of transition metal dichalcogenide (TMDC) nanoparticles (NPs) with the onion-like structure, many efforts have been made to develop their fabrication methods. Laser fabrication (LF) is one of the most promising methods to prepare onion-structured TMDC (or OS-TMDC) NPs due to its green, flexible, and scalable syntheses. In this mini-review article, we systematically introduce various laser-induced OS-TMDC (especially the OS-MoS₂) NPs, their formation mechanism, properties, and applications. The preparation routes mainly include laser ablation in liquids and atmospheres, and laser irradiation in liquids. The various formation mechanisms are then introduced based on the different preparation routes, to describe the formations of the corresponding OS-NPs. Finally, some interesting properties and novel applications of these NPs are briefly demonstrated, and a short outlook is also given. This review could help to understand the progress of the laser-induced OS-TMDC NPs and their applications.

Influence of particle size on the breaking of aluminum particle shells

Tian-Yi Wang(王天一), Zheng-Qing Zhou(周正青), Jian-Ping Peng(彭剑平),Yu-Kun Gao(高玉坤), and Ying-Hua Zhang(张英华)

Chin. Phys. B, 2022, 31 (7): 076107. DOI: 10.1088/1674-1056/ac5615

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Rupturing the alumina shell (shell-breaking) is a prerequisite for releasing energy from aluminum powder. Thermal stress overload in a high-temperature environment is an important factor in the rupture of the alumina shell. COMSOL Multiphysics was used to simulate and analyze the shell-breaking response of micron-scale aluminum particles with different particle sizes at 650 ℃ in vacuum. The simulation results show that the thermal stability time and shell-breaking response time of 10 μm-100 μm aluminum particles are 0.15 μs-11.44 μs and 0.08 μs-3.94 μs, respectively. They also reveal the direct causes of shell breaking for aluminum particles with different particle sizes. When the particle size is less than 80 μm, the shell-breaking response is a direct result of compressive stress overload. When the particle size is between 80 μm and 100 μm, the shell-breaking response is a direct result of tensile stress overload. This article provides useful guidance for research into the energy release of aluminum powder.

High-pressure study of topological semimetals XCd₂Sb₂ (X = Eu and Yb) ^Hot!

Chuchu Zhu(朱楚楚), Hao Su(苏豪), Erjian Cheng(程二建), Lin Guo(郭琳), Binglin Pan(泮炳霖), Yeyu Huang(黄烨煜), Jiamin Ni(倪佳敏), Yanfeng Guo(郭艳峰), Xiaofan Yang(杨小帆), and Shiyan Li(李世燕)

Chin. Phys. B, 2022, 31 (7): 076201. DOI: 10.1088/1674-1056/ac7212

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Topological materials have aroused great interest in recent years, especially when magnetism is involved. Pressure can effectively tune the topological states and possibly induce superconductivity. Here we report the high-pressure study of topological semimetals $X$Cd$_{2}$Sb$_{2}$ ($X = {\rm Eu} $ and Yb), which have the same crystal structure. In antiferromagnetic (AFM) Weyl semimetal EuCd$_{2}$Sb$_{2}$, the Néel temperature (${T}_{\rm N}$) increases from 7.4 K at ambient pressure to 50.9 K at 14.9 GPa. When pressure is above 14.9 GPa, the AFM peak of resistance disappears, indicating a non-magnetic state. In paramagnetic Dirac semimetal candidate YbCd$_{2}$Sb$_{2}$, pressure-induced superconductivity appears at 1.94 GPa, then ${ T}_{\rm c}$ reaches to a maximum of 1.67 K at 5.22 GPa and drops to zero at about 30 GPa, displaying a dome-shaped temperature-pressure phase diagram. High-pressure x-ray diffraction measurement demonstrates that a crystalline-to-amorphous phase transition occurs at about 16 GPa in YbCd$_{2}$Sb$_{2}$, revealing the robustness of pressure-induced superconductivity against structural instability. Similar structural phase transition may also occur in EuCd$_{2}$Sb$_{2}$, causing the disappearance of magnetism. Our results show that $X$Cd$_{2}$Sb$_{2}$ ($X = {\rm Eu}$ and Yb) is a novel platform for exploring the interplay among magnetism, topology, and superconductivity.

Tunable anharmonicity versus high-performance thermoelectrics and permeation in multilayer (GaN)_1-x(ZnO)_x Suggested by editors

Hanpu Liang(梁汉普) and Yifeng Duan(段益峰)

Chin. Phys. B, 2022, 31 (7): 076301. DOI: 10.1088/1674-1056/ac5c38

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Nonisovalent (GaN)$_{1-x}$(ZnO)$_x$ alloys are more technologically promising than their binary counterparts because of the abruptly reduced band gap. Unfortunately, the lack of two-dimensional (2D) configurations as well as complete stoichiometries hinders to further explore the thermal transport, thermoelectrics, and adsorption/permeation. We identify that multilayer (GaN)$_{1-x}$(ZnO)$_x$ stabilize as wurtzite-like $Pm$-(GaN)$_3$(ZnO)$_1$, $Pmc2_1$-(GaN)$_1$(ZnO)$_1$, $P3m1$-(GaN)$_1$(ZnO)$_2$, and haeckelite $C2/m$-(GaN)$_1$(ZnO)$_3$ via structural searches. $P3m1$-(GaN)$_1$(ZnO)$_2$ shares the excellent thermoelectrics with the figure of merit $ZT$ as high as 3.08 at 900 K for the p-type doping due to the ultralow lattice thermal conductivity, which mainly arises from the strong anharmonicity by the interlayer asymmetrical charge distributions. The $p$-$d$ coupling is prohibited from the group theory in $C2/m$-(GaN)$_1$(ZnO)$_3$, which thereby results in the anomalous band structure versus ZnO composition. To unveil the adsorption/permeation of H$^+$, Na$^+$, and OH$^-$ ions in $AA$-stacking configurations, the potential wells and barriers are explored from the Coulomb interaction and the ionic size. Our work is helpful in experimental fabrication of novel optoelectronic and thermoelectric devices by 2D (GaN)$_{1-x}$(ZnO)$_x$ alloys.

Theoretical and experimental study of phase optimization of tapping mode atomic force microscope

Zheng Wei(魏征), An-Jie Peng(彭安杰), Feng-Jiao Bin(宾凤姣), Ya-Xin Chen(陈亚鑫), and Rui Guan(关睿)

Chin. Phys. B, 2022, 31 (7): 076801. DOI: 10.1088/1674-1056/ac4a6d

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Phase image in tapping-mode atomic force microscope (TM-AFM) results from various dissipations in a microcantilever system. The phases mainly reflect the tip-sample contact dissipations which allow the nanoscale characteristics to be distinguished from each other. In this work, two factors affecting the phase and phase contrast are analyzed. It is concluded from the theoretical and experimental results that the phases and phase contrasts in the TM-AFM are related to the excitation frequency and energy dissipation of the system. For a two-component blend, it is theoretically and experimentally proven that there exists an optimal excitation frequency for maximizing the phase contrast. Therefore, selecting the optimal excitation frequency can potentially improve the phase contrast results. In addition, only the key dissipation between the tip and sample is found to accurately reflect the sample properties. Meanwhile, the background dissipation can potentially reduce the contrasts of the phase images and even mask or distort the effective information in the phase images. In order to address the aforementioned issues, a self-excited method is adopted in this study in order to eliminate the effects of the background dissipation on the phases. Subsequently, the real phase information of the samples is successfully obtained. It is shown in this study that the eliminating of the background dissipation can effectively improve the phase contrast results and the real phase information of the samples is accurately reflected. These results are of great significance in optimizing the phases of two-component samples and multi-component samples in atomic force microscope.

Porous AlN films grown on C-face SiC by hydride vapor phase epitaxy Suggested by editors

Jiafan Chen(陈家凡), Jun Huang(黄俊), Didi Li(李迪迪), and Ke Xu(徐科)

Chin. Phys. B, 2022, 31 (7): 076802. DOI: 10.1088/1674-1056/ac597e

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We report the growth of porous AlN films on C-face SiC substrates by hydride vapor phase epitaxy (HVPE). The influences of growth condition on surface morphology, residual strain and crystalline quality of AlN films have been investigated. With the increase of the V/III ratio, the growth mode of AlN grown on C-face 6H-SiC substrates changes from step-flow to pit-hole morphology. Atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman analysis show that cracks appear due to tensile stress in the films with the lowest V/III ratio and the highest V/III ratio with a thickness of about 3 μm. In contrast, under the medium V/III ratio growth condition, the porous film can be obtained. Even when the thickness of the porous AlN film is further increased to 8 μm, the film remains porous and crack-free, and the crystal quality is improved.

Charge density wave states in phase-engineered monolayer VTe₂ ^Hot!

Zhi-Li Zhu(朱知力), Zhong-Liu Liu(刘中流), Xu Wu(武旭), Xuan-Yi Li(李轩熠), Jin-An Shi(时金安), Chen Liu(刘晨), Guo-Jian Qian(钱国健), Qi Zheng(郑琦), Li Huang(黄立), Xiao Lin(林晓), Jia-Ou Wang(王嘉欧), Hui Chen(陈辉), Wu Zhou(周武), Jia-Tao Sun(孙家涛), Ye-Liang Wang(王业亮), and Hong-Jun Gao(高鸿钧)

Chin. Phys. B, 2022, 31 (7): 077101. DOI: 10.1088/1674-1056/ac6739

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Charge density wave (CDW) strongly affects the electronic properties of two-dimensional (2D) materials and can be tuned by phase engineering. Among 2D transitional metal dichalcogenides (TMDs), VTe$_{2}$ was predicted to require small energy for its phase transition and shows unexpected CDW states in its T-phase. However, the CDW state of H-VTe$_{2}$ has been barely reported. Here, we investigate the CDW states in monolayer (ML) H-VTe$_{2}$, induced by phase-engineering from T-phase VTe$_{2}$. The phase transition between T- and H-VTe$_{2}$ is revealed with x-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM) measurements. For H-VTe$_{2}$, scanning tunneling microscope (STM) and low-energy electron diffraction (LEED) results show a robust $2\sqrt 3 \times 2\sqrt 3 $ CDW superlattice with a transition temperature above 450 K. Our findings provide a promising way for manipulating the CDWs in 2D materials and show great potential in its application of nanoelectronics.

Impact of composition ratio on the structure and optical properties of (1-x)MnFe₂O₄/(x)ZnMn₂O₄ nanocomposite Suggested by editors

Zein K. Heiba, Mohamed Bakr Mohamed, Ali A. Alkathiri, Sameh I. Ahmed, A A Alhazime

Chin. Phys. B, 2022, 31 (7): 077102. DOI: 10.1088/1674-1056/ac600f

Abstract ( 252 )

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($1-x$)MnFe$_{2}$O$_{4}$ (MFO)/$x$ZnMn$_{2}$O$_{4}$ (ZMO) ($x=0$, 0.2, 0.5, 0.8, and 1.0) nanocomposite samples were prepared using co-precipitation procedure. The phase percentage, cell parameters, and crystallite size of MFO and ZMO phases in each nanocomposite sample were calculated using Rietveld refinement procedure. The x-ray diffraction (XRD) analysis and Fourier-transform infrared spectroscopy techniques established the variation in the lattice parameters of each phase are due to permutation of all cations among the octahedral and tetrahedral sites of MFO and ZMO. The different oxidation states of different ions in all samples were determined using x-ray photoelectron spectroscopy (XPS) technique. The variation in absorbance of the nanocomposite samples with composition parameter ($x$) is dependent on the wavelength region. The optical bandgap of the nanocomposite samples is decreased as the content of ZMO phase increased. The effect of alloying on the refractive index, extinction coefficient, dielectric constant, optical conductivity, and the nonlinear optical behaviors of all samples were studied in detail. The nanocomposite sample $x=0.5$ disclosed upgraded optical parameters with the highest refractive index, optical conductivity, and PL intensity, which nominate it to be functional in various application fields.

Influence of Rashba spin-orbit coupling on Josephson effect in triplet superconductor/two-dimensional semiconductor/triplet superconductor junctions Suggested by editors

Bin-Hao Du(杜彬豪), Man-Ni Chen(陈嫚妮), and Liang-Bin Hu(胡梁宾)

Chin. Phys. B, 2022, 31 (7): 077201. DOI: 10.1088/1674-1056/ac587e

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We study theoretically Josephson effect in a planar ballistic junction between two triplet superconductors with p-wave orbital symmetries and separated by a two-dimensional (2D) semiconductor channel with strong Rashba spin-orbit coupling. In triplet superconductors, three types of orbital symmetries are considered. We use Bogoliubov-de Gennes formalism to describe quasiparticle propagations through the junction and the supercurrents are calculated in terms of Andreev reflection coefficients. The features of the variation of the supercurrents with the change of the strength of Rashba spin-orbit coupling are investigated in some detail. It is found that for the three types of orbital symmetries considered, both the magnitudes of supercurrent and the current-phase relations can be manipulated effectively by tuning the strength of Rashba spin-orbit coupling. The interplay of Rashba spin-orbit coupling and Zeeman magnetic field on supercurrent is also investigated in some detail.

Current spin polarization of a platform molecule with compression effect

Zhi Yang(羊志), Feng Sun(孙峰), Deng-Hui Chen(陈登辉), Zi-Qun Wang(王子群), Chuan-Kui Wang(王传奎), Zong-Liang Li(李宗良), and Shuai Qiu(邱帅)

Chin. Phys. B, 2022, 31 (7): 077202. DOI: 10.1088/1674-1056/ac4f53

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Using the first-principles method, the spin-dependent transport properties of a novel platform molecule containing a freestanding molecular wire is investigated by simulating the spin-polarized scanning tunneling microscope experiment with Ni tip and Au substrate electrodes. Transport calculations show that the total current increases as the tip gradually approaches to the substrate, which is consistent with the conductance obtained from previous experiment. More interestingly, the spin polarization (SP) of current modulated by compression effect has the completely opposite trend to the total current. Transmission analyses reveal that the reduction of SP of current with compression process originates from the promotion of spin-down electron channel, which is controlled by deforming the molecule wire. In addition, the density of states shows that the SP of current is directly affected by the organic-ferromagnetic spinterface. The weak orbital hybridization between the Ni tip and propynyl of molecule results in high interfacial SP, whereas the breaking of the C $\equiv$ C triple of propynyl in favor of the Ni-C-C bond induces the strong orbital hybridization and restrains the interfacial SP. This work proposes a new way to control and design the SP of current through organic-ferromagnetic spinterface using functional molecular platform.

Anisotropic refraction and valley-spin-dependent anomalous Klein tunneling in a 1T'-MoS₂-based p-n junction

Fenghua Qi(戚凤华) and Xingfei Zhou(周兴飞)

Chin. Phys. B, 2022, 31 (7): 077301. DOI: 10.1088/1674-1056/ac46bf

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We investigate the transport properties of electron in a 1T'-MoS₂-based p-n junction. The anisotropic refraction of electron is found when the electron beam crosses the p-n junction, which brings the phenomenon of valley splitting without any external fields. Moreover, it is found that the valley-spin-dependent anomalous Klein tunneling, i.e., the perfect transmission exists at a nonzero incident angle of valley-spin-dependent electron, happens when the vertical electric field is equal to the critical electric field. These two peculiar properties arise from the same reason that the tilted band structure makes the directions of wavevector and velocity different. Our work designs a special valley splitter without any external fields and finds a new type of Klein tunneling.

Valley-dependent transport in strain engineering graphene heterojunctions

Fei Wan(万飞), X R Wang(王新茹), L H Liao(廖烈鸿), J Y Zhang(张嘉颜),M N Chen(陈梦南), G H Zhou(周光辉), Z B Siu(萧卓彬), Mansoor B. A. Jalil, and Yuan Li(李源)

Chin. Phys. B, 2022, 31 (7): 077302. DOI: 10.1088/1674-1056/ac5613

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We study the effect of strain on band structure and valley-dependent transport properties of graphene heterojunctions. It is found that valley-dependent separation of electrons can be achieved by utilizing strain and on-site energies. In the presence of strain, the values of transmission can be effectively adjusted by changing the strengths of the strain, while the transport angle basically keeps unchanged. When an extra on-site energy is simultaneously applied to the central scattering region, not only are the electrons of valleys K and K' separated into two distinct transmission lobes in opposite transverse directions, but the transport angles of two valleys can be significantly changed. Therefore, one can realize an effective modulation of valley-dependent transport by changing the strength and stretch angle of the strain and on-site energies, which can be exploited for graphene-based valleytronics devices.

Effect of crystallographic orientations on transport properties of methylthiol-terminated permethyloligosilane molecular junction

Ming-Lang Wang(王明郎), Bo-Han Zhang(张博涵), Wen-Fei Zhang(张雯斐), Xin-Yue Tian(田馨月), Guang-Ping Zhang(张广平), and Chuan-Kui Wang(王传奎)

Chin. Phys. B, 2022, 31 (7): 077303. DOI: 10.1088/1674-1056/ac4cbf

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The understanding of the influence of electrode characteristics on charge transport is essential in the field of molecular electronics. In this work, we investigate the electronic transport properties of molecular junctions comprising methylthiol-terminated permethyloligosilanes and face-centered crystal Au/Ag electrodes with crystallographic orientations of (111) and (100), based on the ab initio quantum transport simulations. The calculations reveal that the molecular junction conductance is dominated by the electronic coupling between two interfacial metal-S bonding states, which can be tuned by varying the molecular length, metal material of the electrodes, and crystallographic orientation. As the permethyloligosilane backbone elongates, although the σ conjugation increases, the decreasing of coupling induced by the increasing number of central Si atoms reduces the junction conductance. The molecular junction conductance of methylthiol-terminated permethyloligosilanes with Au electrodes is higher than that with Ag electrodes with a crystallographic orientation of (111). However, the conductance trend is reversed when the electrode crystallographic orientation varies from (111) to (100), which can be ascribed to the reversal of interfacial coupling between two metal-S interfacial states. These findings are conducive to elucidating the mechanism of molecular junctions and improving the transport properties of molecular devices by adjusting the electrode characteristics.

Half-metallicity induced by out-of-plane electric field on phosphorene nanoribbons

Xiao-Fang Ouyang(欧阳小芳) and Lu Wang(王路)

Chin. Phys. B, 2022, 31 (7): 077304. DOI: 10.1088/1674-1056/ac560d

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Exploring the half-metallic nanostructures with large band gap and high carrier mobility is a crucial solution for developing high-performance spintronic devices. The electric and magnetic properties of monolayer zigzag black-phosphorene nanoribbons (ZBPNRs) with various widths are analyzed by means of the first-principles calculations. Our results show that the magnetic ground state is dependent on the width of the nanoribbons. The ground state of narrow nanoribbons smaller than 8ZBPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. In addition, we also calculate the electronic band dispersion, density of states and charge density difference of 8ZBPNRs under the action of out-of-plane electric field. More interesting, the addition of out-of-plane field can modulate antiferromagnetic semiconductor to the half metal by splitting the antiferromagnetic degeneracy. Our results propose a new approach to realize half-metal in phosphorene, which overcomes the drawbacks of graphene/silicene with negligible band gap as well as the transitional metal sulfide (TMS) with low carrier mobility.

SERS activity of carbon nanotubes modified by silver nanoparticles with different particle sizes

Xiao-Lei Zhang(张晓蕾), Jie Zhang(张洁), Yuan Luo(罗元), and Jia Ran(冉佳)

Chin. Phys. B, 2022, 31 (7): 077401. DOI: 10.1088/1674-1056/ac4f51

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A two-dimensional (2D) surface-enhanced Raman scattering (SERS) substrate is fabricated by decorating carbon nanotube (CNT) films with Ag nanoparticles (AgNPs) in different sizes, via simple and low-cost chemical reduction method and self-assembling method. The change of Raman and SERS activity of carbon nanotubes/Ag nanoparticles (CNTs/AgNPs) composites with varying size of AgNPs are investigated by using rhodamine 6G (R6G) as a probe molecule. Meanwhile, the scattering cross section of AgNPs and the distribution of electric field of CNTs/AgNPs composite are simulated through finite difference time domain (FDTD) method. Surface plasmon resonance (SPR) wavelength is redshifted as the size of AgNPs increases, and the intensity of SERS and electric field increase with AgNPs size increasing. The experiment and simulation results show a Raman scattering enhancement factor (EF) of 10⁸ for the hybrid substrate.

Large inverse and normal magnetocaloric effects in HoBi compound with nonhysteretic first-order phase transition

Yan Zhang(张艳), You-Guo Shi(石友国), Li-Chen Wang(王利晨), Xin-Qi Zheng(郑新奇), Jun Liu(刘俊), Ya-Xu Jin(金亚旭), Ke-Wei Zhang(张克维), Hong-Xia Liu(刘虹霞), Shuo-Tong Zong(宗朔通), Zhi-Gang Sun(孙志刚), Ji-Fan Hu(胡季帆), Tong-Yun Tong(赵同云), and Bao-Gen Shen(沈保根)

Chin. Phys. B, 2022, 31 (7): 077501. DOI: 10.1088/1674-1056/ac597f

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HoBi single crystal and polycrystalline compounds with NaCl-type structure are successfully obtained, and their magnetic and magnetocaloric properties are studied in detail. With temperature increasing, HoBi compound undergoes two magnetic transitions at 3.7 K and 6 K, respectively. The transition temperature at 6 K is recognized as an antiferromagnetic-to-paramagnetic (AFM-PM) transition, which belongs to the first-order magnetic phase transition (FOMT). It is interesting that the HoBi compound with FOMT exhibits good thermal and magnetic reversibility. Furthermore, a large inverse and normal magnetocaloric effect (MCE) is found in HoBi single crystal in the $H|| [100]$ direction, and the positive $\Delta S_{\rm M}$ peak reaches 13.1 J/kg$\cdot$K under a low field change of 2 T and the negative $\Delta S_{\rm M}$ peak arrives at $-18 $ J/kg$\cdot$K under a field change of 5 T. These excellent properties are expected to be applied to some magnetic refrigerators with special designs and functions.

Voltage control magnetism and ferromagnetic resonance in an Fe₁₉Ni₈₁/PMN-PT heterostructure by strain Suggested by editors

Jun Ren(任军), Junming Li(李军明), Sheng Zhang(张胜), Jun Li(李骏), Wenxia Su(苏文霞), Dunhui Wang(王敦辉), Qingqi Cao(曹庆琪), and Youwei Du(都有为)

Chin. Phys. B, 2022, 31 (7): 077502. DOI: 10.1088/1674-1056/ac43ab

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Voltage control magnetism has been widely studied due to its potential applications in the next generation of information technology. PMN-PT, as a single crystal ferroelectric substrate, has been widely used in the study of voltage control magnetism because of its excellent piezoelectric properties. However, most of the research based on PMN-PT only studies the influence of a single tensile (or compressive) stress on the magnetic properties due to the asymmetry of strain. In this work, we show the effect of different strains on the magnetic anisotropy of an Fe₁₉Ni₈₁/(011) PMN-PT heterojunction. More importantly, the (011) cut PMN-PT generates non-volatile strain, which provides an advantage when investigating the voltage manipulation of RF/microwave magnetic devices. As a result, a ferromagnetic resonance field tunability of 70 Oe is induced in our sample by the non-volatile strain. Our results provide new possibilities for novel voltage adjustable RF/microwave magnetic devices and spintronic devices.

Synchronization of nanowire-based spin Hall nano-oscillators Suggested by editors

Biao Jiang(姜彪), Wen-Jun Zhang(张文君), Mehran Khan Alam, Shu-Yun Yu(于淑云), Guang-Bing Han(韩广兵), Guo-Lei Liu(刘国磊), Shi-Shen Yan(颜世申), and Shi-Shou Kang(康仕寿)

Chin. Phys. B, 2022, 31 (7): 077503. DOI: 10.1088/1674-1056/ac560a

Abstract ( 301 )

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The synchronization of the spin Hall nano-oscillator (SHNO) device driven by the pure spin current has been investigated with micromagnetic simulations. It was found that the power spectra of nanowire-based SHNO devices can be synchronized by varying the current flowing in the heavy metal (HM) layer. The synchronized signals have relatively high power and narrow linewidth, favoring the potential applications. We also found that the synchronized spectra are strongly dependent on both the number and length of nanowires. Moreover, a periodic modulation of power spectra can be obtained by introducing interfacial Dzyaloshinskii-Moriya interaction (iDMI). Our findings could enrich the current understanding of spin dynamics driven by the pure spin current. Further, it could help to design novel spintronic devices.

Current-driven dynamics of skyrmion bubbles in achiral uniaxial magnets Suggested by editors

Yaodong Wu(吴耀东), Jialiang Jiang(蒋佳良), and Jin Tang(汤进)

Chin. Phys. B, 2022, 31 (7): 077504. DOI: 10.1088/1674-1056/ac6db1

Abstract ( 249 )

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We report dynamics of skyrmion bubbles driven by spin-transfer torque in achiral ferromagnetic nanostripes using micromagnetic simulations. In a three-dimensional uniaxial ferromagnet with a quality factor that is smaller than 1, the skyrmion bubble is forced to stay at the central nanostripe by a repulsive force from the geometry border. The coherent motion of skyrmion bubbles in the nanostripe can be realized by increasing the quality factor to ～ 3.8. Our results should propel the design for future spintronic devices such as artificial neural computing and racetrack memory based on dipole-stabilized skyrmion bubbles.

Improved performance of MoS₂ FET by in situ NH₃ doping in ALD Al₂O₃ dielectric

Xiaoting Sun(孙小婷), Yadong Zhang(张亚东), Kunpeng Jia(贾昆鹏), Guoliang Tian(田国良), Jiahan Yu(余嘉晗), Jinjuan Xiang(项金娟), Ruixia Yang(杨瑞霞), Zhenhua Wu(吴振华), and Huaxiang Yin(殷华湘)

Chin. Phys. B, 2022, 31 (7): 077701. DOI: 10.1088/1674-1056/ac3bab

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Since defects such as traps and oxygen vacancies exist in dielectrics, it is difficult to fabricate a high-performance MoS$_{2}$ field-effect transistor (FET) using atomic layer deposition (ALD) Al$_{2}$O$_{3}$ as the gate dielectric layer. In this paper, NH$_{3}$ in situ doping, a process treatment approach during ALD growth of Al$_{2}$O$_{3}$, is used to decrease these defects for better device characteristics. MoS$_{2}$ FET has been well fabricated with this technique and the effect of different NH$_{3}$ in situ doping sequences in the growth cycle has been investigated in detail. Compared with counterparts, those devices with NH$_{3}$ in situ doping demonstrate obvious performance enhancements: $I_{\rm on}/I_{\rm off}$ is improved by one order of magnitude, from $1.33\times 10^{5}$ to $3.56\times 10^{6}$, the threshold voltage shifts from $-0.74 $ V to $-0.12$ V and a small subthreshold swing of 105 mV/dec is achieved. The improved MoS$_{2}$ FET performance is attributed to nitrogen doping by the introduction of NH$_{3}$ during the Al$_{2}$O$_{3}$ ALD growth process, which leads to a reduction in the surface roughness of the dielectric layer and the repair of oxygen vacancies in the Al$_{2}$O$_{3}$ layer. Furthermore, the MoS$_{2}$ FET processed by in situ NH$_{3}$ doping after the Al and O precursor filling cycles demonstrates the best performance; this may be because the final NH$_{3}$ doping after film growth restores more oxygen vacancies to screen more charge scattering in the MoS$_{2}$ channel. The reported method provides a promising way to reduce charge scattering in carrier transport for high-performance MoS$_{2 }$ devices.

Design of a low-frequency miniaturized piezoelectric antenna based on acoustically actuated principle

Yong Zhang(张勇), Zhong-Ming Yan(严仲明), Tian-Hao Han(韩天浩), Shuang-Shuang Zhu(朱双双), Yu Wang(王豫), and Hong-Cheng Zhou(周洪澄)

Chin. Phys. B, 2022, 31 (7): 077702. DOI: 10.1088/1674-1056/ac6495

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An acoustically actuated piezoelectric antenna is proposed for low frequency (LF) band in this paper. The proposed antenna is theoretically calculated, numerically optimized by the finite element method (FEM), and experimentally analyzed. The measurement results show that the near-field radiation pattern of the piezoelectric antenna is similar to that of the electric dipole antenna. The radiation efficiency of the piezoelectric antenna is 3－4 orders of magnitude higher than that of electrically small antenna (ESA), with their sizes being the same size, and the maximum transmission distance obtained experimentally is 100 cm, which can be improved by increasing the input power. In addition, the gain, directivity, and quality factor of piezoelectric antenna are also analyzed. In this paper, traditional antenna parameters are creatively used to analyze the performance of piezoelectric antenna. The research conclusions can provide reliable theoretical basis for realizing LF antenna miniaturization.

Effect of surface plasmon coupling with radiating dipole on the polarization characteristics of AlGaN-based light-emitting diodes

Yi Li(李毅), Mei Ge(葛梅), Meiyu Wang(王美玉), Youhua Zhu(朱友华), and Xinglong Guo(郭兴龙)

Chin. Phys. B, 2022, 31 (7): 077801. DOI: 10.1088/1674-1056/ac4cbb

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The optical polarization characteristics of surface plasmon (SP) coupled AlGaN-based light emitting diodes (LEDs) are investigated theoretically by analyzing the radiation recombination process and scattering process respectively. For the Al_0.5Ga_0.5N/Al/Al₂O₃ slab structure, the relative intensity of TE-polarized and TM-polarized spontaneous emission (SE) rate into the SP mode obviously depends on the thickness of the Al layer. The calculation results show that TM dominated emission will be transformed into TE dominated emission with the decrease of the Al thickness, while the emission intensities of both TE/TM polarizations will decrease significantly. In addition, compared with TM polarized emission, TE polarized emission is easier to be extracted by SP coupling. For the Al_0.5Ga_0.5N/Al nano-particle structure, the ratio of transmittance for TE/TM polarized emission can reach ～3.06, while for the Al free structure, it is only 1.2. Thus, the degree of polarization of SP coupled LED can be improved by the reasonable structural design.

Design optimization of broadband extreme ultraviolet polarizer in high-dimensional objective space

Shang-Qi Kuang(匡尚奇), Bo-Chao Li(李博超), Yi Wang(王依), Xue-Peng Gong(龚学鹏), and Jing-Quan Lin(林景全)

Chin. Phys. B, 2022, 31 (7): 077802. DOI: 10.1088/1674-1056/ac4a64

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With the purpose of designing the extreme ultraviolet polarizer with many objectives, a combined application of multi-objective genetic algorithms is theoretically proposed. Owing to the multi-objective genetic algorithm, the relationships between different designing objectives of extreme ultraviolet polarizer have been obtained by analyzing the distribution of nondominated solutions in the four-dimensional objective space, and the optimized multilayer design can be obtained by guiding the searching in the desired region based on the multi-objective genetic algorithm with reference direction. Compared with the conventional method of multilayer design, our method has a higher probability of achieving the optimal multilayer design. Our work should be the first research in optimizing the optical multilayer designs in the high-dimensional objective space, and our results demonstrate a potential application of our method in the designs of optical thin films.

Quantitative evaluation of LAL productivity of colloidal nanomaterials: Which laser pulse width is more productive, ergonomic, and economic?

Alena Nastulyavichus, Nikita Smirnov, and Sergey Kudryashov

Chin. Phys. B, 2022, 31 (7): 077803. DOI: 10.1088/1674-1056/ac5602

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Near-IR (wavelength ≈ 1 μm) laser ablation of bulk, chemically-inert gold in water was compared for different laser pulse width in broad the range of 300 fs-100 ns, comparing a number of key ablation characteristics: mass loss, single-shot crater volume and extinction coefficient of the generated colloidal solutions taken in the spectral ranges of interband transitions and localized plasmon resonance. Comparing to related air-based ablation results, at the given fluences laser ablation in the liquid resulted in the maximum ablation yield per unit energy and maximum NP yield per pulse and per unit energy for the picosecond lasers, occurring at subcritical peak pulse powers for laser self-focusing. The self-focusing effect was demonstrated to yield in incomplete, effectively weaker focusing in the water filaments of ultrashort laser pulses with supercritical peak powers, comparing to linear (geometrical) focusing at sub-critical peak powers. At the other, nanosecond-pulse extreme the high ablation yield per pulse, but low ablation yield per unit energy and low NP yield per pulse and per unit energy were related to strong ablation plasma screening, providing mass removal according to the well-established scaling relationships for plasma. Illustrative comparison of the ablation and nanoparticle generation efficiency versus the broad fs-ns laser pulse width range was enabled in terms of productivity, economicity, and ergonomicity, using the proposed universal quantitative criteria.

Laser fragmentation in liquid synthesis of novel palladium-sulfur compound nanoparticles as efficient electrocatalysts for hydrogen evolution reaction

Guo-Shuai Fu(付国帅), Hong-Zhi Gao(高宏志), Guo-Wei Yang(杨国伟), Peng Yu(于鹏), and Pu Liu(刘璞)

Chin. Phys. B, 2022, 31 (7): 077901. DOI: 10.1088/1674-1056/ac4e0e

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One promising way to tune the physicochemical properties of materials and optimize their performance in various potential applications is to engineer material structures at the atomic level. As is well known, the performance of Pd-based catalysts has long been constrained by surface contamination and their single structure. Here, we employed an unadulterated top-down synthesis method, known as laser fragmentation in liquid (LFL), to modify pristine PdPS crystals and obtained a kind of metastable palladium-sulfur compound nanoparticles (LFL-PdS NPs) as a highly efficient electrocatalyst for hydrogen evolution reaction (HER). Laser fragmentation of the layered PdPS crystal led to a structural reorganization at the atomic level and resulted in the formation of uniform metastable LFL-PdS NPs. Noteworthy, the LFL-PdS NPs show excellent electrocatalytic HER performance and stability in acidic media, with an overpotential of -66 mV at 10 mA· cm^-2, the Tafel slope of 42 mV· dec^-1. The combined catalytic performances of our LFL-PdS NPs are comparable to the Pt/C catalyst for HER. This work provides a top-down synthesis strategy as a promising approach to design highly active metastable metal composite electrocatalysts for sustainable energy applications.

Probing the improved stability for high nickel cathode via dual-element modification in lithium-ion Suggested by editors

Fengling Chen(陈峰岭), Chaozhi Zeng(曾朝智), Chun Huang(黄淳), Jiannan Lin(林建楠), Yifan Chen(陈一帆), Binbin Dong(董彬彬), Chujun Yin(尹楚君), Siying Tian(田飔莹), Dapeng Sun(孙大鹏), Zhenyu Zhang(张振宇), Hong Li(李泓), and Chaobo Li(李超波)

Chin. Phys. B, 2022, 31 (7): 078101. DOI: 10.1088/1674-1056/ac598c

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One of the major hurdles of nickel-rich cathode materials for lithium-ion batteries is the low cycling stability, especially at high temperature and high voltage, originating from severe structural degradation, which makes this class of cathode less practical. Herein, we compared the effect of single and dual ions on electrochemical performance of high nickel (LiNi_0.88Mn_0.03Co_0.09O₂, NMC) cathode material in different temperatures and voltage ranges. The addition of a few amounts of tantalum (0.2 wt%) and boron (0.05 wt%) lead to improved electrochemical performance. The co-modified LiNi_0.88Mn_0.03Co_0.09O₂ displays an initial discharge capacity of 234.9 mAh/g at 0.1 C and retained 208 mAh/g at 1 C after 100 cycles at 45 ℃, which corresponds to a capacity retention of 88.5%, compared to the initial discharge capacity of 234.1 mAh/g and retained capacity of 200.5 mAh/g (85.6%). The enhanced capacity retention is attributed to the synergetic effect of foreign elements by acting as a surface structural stabilizer without sacrificing specific capacity.

Novel closed-cycle reaction mode for totally green production of Cu_1.8Se nanoparticles based on laser-generated Se colloidal solution

Zhangyu Gu(顾张彧), Yisong Fan(范一松), Yixing Ye(叶一星), Yunyu Cai(蔡云雨), Jun Liu(刘俊), Shouliang Wu(吴守良), Pengfei Li(李鹏飞), Junhua Hu(胡俊华), Changhao Liang(梁长浩), and Yao Ma(马垚)

Chin. Phys. B, 2022, 31 (7): 078102. DOI: 10.1088/1674-1056/ac6db2

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Non-stoichiometric copper selenide (Cu_2-xSe, x=0.18～0.25) nanomaterials have attracted extensive attentions due to their excellent thermoelectric, optoelectronic and photocatalytic performances. However, efficient production of Cu_2-xSe nanoparticles (NPs) through a green and convenient way is still hindered by the inevitable non-environmentally friendly operations in common chemical synthesis. Herein, we initially reveal the coexistence of seleninic acid content and elemental selenium (Se) NPs in pulsed laser-generated Se colloidal solution. Consequently, we put forward firstly a closed-cycle reaction mode for totally green production of Cu_1.8Se NPs to exclude traditional requirements of high temperature and toxic precursors by using Se colloidal solution. In such closed-cycle reaction, seleninic acid works as the initiator to oxidize copper sheet to release cuprous ions which can catalyze the disproportion of Se NPs to form SeO₃^2- and Se^2- ions and further produce Cu_2-xSe NPs, and the by-product SeO₃^2- ions promote subsequent formation of cuprous from the excessive Cu sheet. In experiments, the adequate copper (Cu) sheet was simply dipped into such Se colloidal solution at 70 ℃, and then the stream of Cu_1.8Se NPs could be produced until the exhaustion of selenium source. The conversion rate of Se element reaches to more than 75% when the size of Se NPs in weakly acidic colloidal solution is limited between 1 nm and 50 nm. The laser irradiation duration shows negative correlation with the size of Se NPs and unobvious impact to the pH of the solution which both are essential to the high yield of Cu_1.8Se NPs. Before Cu sheet is exhausted, Se colloidal solution can be successively added without influences to the product quality and the Se conversion rate. Such green methodology positively showcases a brand-new and potential strategy for mass production of Cu_2-xSe nanomaterials.

Probing component contributions and internal polarization in silicon-graphite composite anode for lithium-ion batteries with an electrochemical-mechanical model ^Hot!

Yue Chen(陈约), Fuliang Guo(郭福亮), Lufeng Yang(杨陆峰), Jiaze Lu(卢嘉泽), Danna Liu(刘丹娜), Huayu Wang(王华宇), Jieyun Zheng(郑杰允), Xiqian Yu(禹习谦), and Hong Li(李泓)

Chin. Phys. B, 2022, 31 (7): 078201. DOI: 10.1088/1674-1056/ac6012

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Silicon-graphite (Si-Gr) composite anodes are attractive alternatives to replace Gr anodes for lithium-ion batteries (LIBs) owing to their relatively high capacity and mild volume change. However, it is difficult to understand electrochemical interactions of Si and Gr in Si-Gr composite anodes and internal polarization of LIBs with regular experiment methods. Herein, we establish an electrochemical-mechanical coupled model to study the effect of rate and Si content on the electrochemical and stress behavior in a Si-Gr composite anode. The results show that the composites of Si and Gr not only improve the lithiation kinetics of Gr but also alleviate the voltage hysteresis of Si and decrease the risk of lithium plating in the negative electrode. What's more, the Si content is a tradeoff between electrode capacity and electrode volume variation. Further, various internal polarization contributions of cells using Si-Gr composite anodes are quantified by the voltage decomposition method. The results indicate that the electrochemical polarization of electrode materials and the electrolyte ohmic over-potential are dominant factors in the rate performance of cells, which provides theoretical guidance for improving the rate performance of LIBs using Si-Gr composite anodes.

Switchable and tunable triple-channel bandpass filter

Ming-En Tian(田明恩), Zhi-He Long(龙之河), Li-Jun Feng(冯丽君), Lei-Lei He(贺磊磊), and Tian-Liang Zhang(张天良)

Chin. Phys. B, 2022, 31 (7): 078401. DOI: 10.1088/1674-1056/ac4f4f

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A triple-channel bandpass filter with switchable and tunable functions is proposed, which is based on a triple-mode cross resonator. The varactors and switching diodes are loaded at the end of the resonator. Because of the use of switches, resonators have four working states: conventional single-mode, two dual-modes, and one triple-mode. The varactor makes the channel independently adjustable. Finally, a triple-channel bandpass filter with switchable and tunable functions is designed by using two identical triple-mode resonator coupling structures. To solve the problem of whether each channel in the multi-channel filter is independently adjustable, this paper gives a simple and rigorous judgment method, namely rank criterion, which is a necessary and sufficient condition for each channel to be independently adjustable. The method of designing an element variable coupling matrix (EVCM) is adopted, which can not only obtain the desired frequency response through adjustable elements but also help to select resonators and coupling modes in the actual circuit design. The final circuit size of the designed filter is 0.29 λg×0.26 λg. The measured results are in good agreement with the simulation results.

Machine learning potential aided structure search for low-lying candidates of Au clusters Suggested by editors

Tonghe Ying(应通和), Jianbao Zhu(朱健保), and Wenguang Zhu(朱文光)

Chin. Phys. B, 2022, 31 (7): 078402. DOI: 10.1088/1674-1056/ac5c3d

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A machine learning (ML) potential for Au clusters is developed through training on a dataset including several different sized clusters. This ML potential accurately covers the whole configuration space of Au clusters in a broad size range, thus expressing a good performance in search of their global minimum energy structures. Based on our potential, the low-lying structures of 17 different sized Au clusters are identified, which shows that small sized Au clusters tend to form planar structures while large ones are more likely to be stereo, revealing the critical size for the two-dimensional (2D) to three-dimensional (3D) structural transition. Our calculations demonstrate that ML is indeed powerful in describing the interaction of Au atoms and provides a new paradigm on accelerating the search of structures.

Switchable down-, up- and dual-chirped microwave waveform generation with improved time-bandwidth product based on polarization modulation and phase encoding

Yuxiao Guo(郭玉箫), Muguang Wang(王目光), Hongqian Mu(牟宏谦), and Guofang Fan(范国芳)

Chin. Phys. B, 2022, 31 (7): 078403. DOI: 10.1088/1674-1056/ac5982

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A switchable down-, up- and dual-chirped microwave waveform generation technique with improved time-bandwidth product (TBWP) is proposed and demonstrated based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) cascaded with a polarization modulator (PolM). By properly controlling the phase shifts of the radio frequency signals applied to the DP-DPMZM, switchable down-, up- and dual-chirped waveforms with simultaneous frequency and bandwidth doubling can be generated. To enlarge the TBWP further, splitting parabolic signal and phase-encoding splitting parabolic signal are used to drive the PolM for the enhancement of bandwidth and time duration. Numerical results demonstrate the generation of down-, up- and dual-chirped microwave waveform with TBWP of 8, 160 and 10240. The proposed method may find applications in future multifunction radar systems due to the high performance and flexibility.

A 4H-SiC trench MOSFET structure with wrap N-type pillar for low oxide field and enhanced switching performance

Pei Shen(沈培), Ying Wang(王颖), and Fei Cao(曹菲)

Chin. Phys. B, 2022, 31 (7): 078501. DOI: 10.1088/1674-1056/ac4e08

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An optimized silicon carbide (SiC) trench metal-oxide-semiconductor field-effect transistor (MOSFET) structure with side-wall p-type pillar (p-pillar) and wrap n-type pillar (n-pillar) in the n-drain was investigated by utilizing Silvaco TCAD simulations. The optimized structure mainly includes a p$+$ buried region, a light n-type current spreading layer (CSL), a p-type pillar region, and a wrapping n-type pillar region at the right and bottom of the p-pillar. The improved structure is named as SNPPT-MOS. The side-wall p-pillar region could better relieve the high electric field around the p$+$ shielding region and the gate oxide in the off-state mode. The wrapping n-pillar region and CSL can also effectively reduce the specific on-resistance ($R_{\rm on,sp}$). As a result, the SNPPT-MOS structure exhibits that the figure of merit (FoM) related to the breakdown voltage ($V_{\rm BR}$) and $R_{\rm on,sp}$ ($V_{\rm BR}^{2}R_{\rm on,sp}$) of the SNPPT-MOS is improved by 44.5%, in comparison to that of the conventional trench gate SJ MOSFET (full-SJ-MOS). In addition, the SNPPT-MOS structure achieves a much faster-witching speed than the full-SJ-MOS, and the result indicates an appreciable reduction in the switching energy loss.

Fabrication and investigation of ferroelectric memristors with various synaptic plasticities

Qi Qin(秦琦), Miaocheng Zhang(张缪城), Suhao Yao(姚苏昊), Xingyu Chen(陈星宇), Aoze Han(韩翱泽),Ziyang Chen(陈子洋), Chenxi Ma(马晨曦), Min Wang(王敏), Xintong Chen(陈昕彤), Yu Wang(王宇),Qiangqiang Zhang(张强强), Xiaoyan Liu(刘晓燕), Ertao Hu(胡二涛), Lei Wang(王磊), and Yi Tong(童祎)

Chin. Phys. B, 2022, 31 (7): 078502. DOI: 10.1088/1674-1056/ac3ece

Abstract ( 329 )

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In the post-Moore era, neuromorphic computing has been mainly focused on breaking the von Neumann bottlenecks. Memristors have been proposed as a key part of neuromorphic computing architectures, and can be used to emulate the synaptic plasticities of the human brain. Ferroelectric memristors represent a breakthrough for memristive devices on account of their reliable nonvolatile storage, low write/read latency and tunable conductive states. However, among the reported ferroelectric memristors, the mechanisms of resistive switching are still under debate. In addition, there needs to be more research on emulation of the brain synapses using ferroelectric memristors. Herein, Cu/PbZr_0.52Ti_0.48O₃ (PZT)/Pt ferroelectric memristors have been fabricated. The devices are able to realize the transformation from threshold switching behavior to resistive switching behavior. The synaptic plasticities, including excitatory post-synaptic current, paired-pulse facilitation, paired-pulse depression and spike time-dependent plasticity, have been mimicked by the PZT devices. Furthermore, the mechanisms of PZT devices have been investigated by first-principles calculations based on the interface barrier and conductive filament models. This work may contribute to the application of ferroelectric memristors in neuromorphic computing systems.

Microstructural, magnetic and dielectric performance of rare earth ion (Sm³⁺)-doped MgCd ferrites

Dandan Wen(文丹丹), Xia Chen(陈霞), Dasen Luo(骆大森), Yi Lu(卢毅),Yixin Chen(陈一鑫), Renpu Li(黎人溥), and Wei Cui(崔巍)

Chin. Phys. B, 2022, 31 (7): 078503. DOI: 10.1088/1674-1056/ac398c

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The combined effects of Sm$^{3+}$ substitution together with the addition of 3 wt% Bi$_{2}$O$_{3}$ endow MgCd ferrites with excellent magnetic permeability and dielectric permittivity. Various concentrations of Sm$^{3+}$ ($x = 0$, 0.03, 0.06, 0.09, 0.12 and 0.15) were employed to modify the permeability ($\mu'$) and permittivity ($\varepsilon'$) of the MgCd ferrites. X-ray diffraction, scanning electron microscopy (SEM), vibrating sample magnetometry and vector network analysis techniques were used to characterize the samples. The measurement results reveal that the ferrites processed a saturation magnetization of up to 36.8 emu/g and coercivity of up to 29.2 Oe via the conventional solid-state reaction method. The surface morphology SEM confirms that with increasing Sm$^{3+}$ concentration, the grain shape changes from a polygon to a circle. Moreover, the dielectric permittivity can reach a value of 23. The excellent properties obtained in Sm$^{3+}$-substituted Mg ferrites suggest that they could be promising candidates for modern high-frequency antenna substrates or multilayer devices.

Up/down-conversion luminescence of monoclinic Gd₂O₃:Er³⁺ nanoparticles prepared by laser ablation in liquid

Hua-Wei Deng(邓华威) and Di-Hu Chen(陈弟虎)

Chin. Phys. B, 2022, 31 (7): 078701. DOI: 10.1088/1674-1056/ac5399

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Multifunctional luminescent materials are attracting attention nowadays. In this work, monoclinic Gd₂O₃:Er³⁺ nanoparticles, which possess up-conversion luminescence and down-conversion luminescence properties, were successfully synthesized by laser ablation in liquid (LAL) technique. Up-conversion luminescence and down-conversion luminescence of monoclinic Gd₂O₃:Er³⁺ nanoparticles were got under the excitation of 980 nm and 379 nm, respectively. In addition, tunable luminescence was got. Furthermore, the cytotoxicity of the nanoparticles is low and the fluorescence of the nanoparticles in cell is also strong enough. The results indicate that the Gd₂O₃:Er³⁺ nanoparticles synthesized by LAL technique are promising candidates for bio-imaging or other fields that require controllable fluorescence.

Pulse coding off-chip learning algorithm for memristive artificial neural network

Ming-Jian Guo(郭明健), Shu-Kai Duan(段书凯), and Li-Dan Wang(王丽丹)

Chin. Phys. B, 2022, 31 (7): 078702. DOI: 10.1088/1674-1056/ac4f4e

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Memristive neural network has attracted tremendous attention since the memristor array can perform parallel multiply-accumulate calculation (MAC) operations and memory-computation operations as compared with digital CMOS hardware systems. However, owing to the variability of the memristor, the implementation of high-precision neural network in memristive computation units is still difficult. Existing learning algorithms for memristive artificial neural network (ANN) is unable to achieve the performance comparable to high-precision by using CMOS-based system. Here, we propose an algorithm based on off-chip learning for memristive ANN in low precision. Training the ANN in the high-precision in digital CPUs and then quantifying the weight of the network to low precision, the quantified weights are mapped to the memristor arrays based on VTEAM model through using the pulse coding weight-mapping rule. In this work, we execute the inference of trained 5-layers convolution neural network on the memristor arrays and achieve an accuracy close to the inference in the case of high precision (64-bit). Compared with other algorithms-based off-chip learning, the algorithm proposed in the present study can easily implement the mapping process and less influence of the device variability. Our result provides an effective approach to implementing the ANN on the memristive hardware platform.

Passenger management strategy and evacuation in subway station under Covid-19 Suggested by editors

Xiao-Xia Yang(杨晓霞), Hai-Long Jiang(蒋海龙), Yuan-Lei Kang(康元磊), Yi Yang(杨毅), Yong-Xing Li(李永行), and Chang Yu(蔚畅)

Chin. Phys. B, 2022, 31 (7): 078901. DOI: 10.1088/1674-1056/ac43b3

Abstract ( 458 )

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Under the background of Covid-19 sweeping the world, safe and reasonable passenger flow management strategy in subway stations is an effective means to prevent the spread of virus. Based on the social force model and the minimum cost model, the movement and path selection behavior of passengers in the subway station are modeled, and a strategy for passenger flow management to maintain a safe social distance is put forward. Take Qingdao Jinggangshan Road subway station of China as the simulation scene, the validity of the simulation model is verified by comparing the measured value and simulation value of the time required for passengers from getting off the train to the ticket gate. Simulation results indicate that controlling the time interval between incoming passengers at the entrance can effectively control the social distance between passengers and reduce the risk of epidemic infection. By comparing the evacuation process of passengers under different initial densities, it is found that the greater the initial density of passengers is, the longer the passengers are at risk social distance. In the process of passenger emergency evacuation, the stairs/escalators and ticket gates are bottleneck areas with high concentration of passenger density, which should be strictly disinfected many times on the basis of strictly checking the health code of incoming passengers and controlling the arrival time interval. The simulation results of this paper verify the harmfulness of passenger emergency evacuation without protective measures, and provide theoretical support for the operation and management of subway station under the epidemic situation.

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