中国物理B

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Exploring Majorana zero modes in iron-based superconductors

Geng Li(李更), Shiyu Zhu(朱诗雨), Peng Fan(范朋), Lu Cao(曹路), and Hong-Jun Gao(高鸿钧)

2022 (8): 80301-080301. doi: 10.1088/1674-1056/ac70c3

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Majorana zero modes (MZMs) are Majorana-fermion-like quasiparticles existing in crystals or hybrid platforms with topologically non-trivial electronic structures. They obey non-Abelian braiding statistics and are considered promising to realize topological quantum computing. Discovery of MZM in the vortices of the iron-based superconductors (IBSs) has recently fueled the Majorana research in a way which not only removes the material barrier requiring construction of complicated hybrid artificial structures, but also enables observation of pure MZMs under higher temperatures. So far, MZMs have been observed in iron-based superconductors including FeTe_0.55Se_0.45, (Li_0.84Fe_0.16)OHFeSe, CaKFe₄As₄, and LiFeAs. In this topical review, we present an overview of the recent STM studies on the MZMs in IBSs. We start with the observation of MZMs in the vortices in FeTe_0.55Se_0.45 and discuss the pros and cons of FeTe_0.55Se_0.45 compared with other platforms. We then review the following up discovery of MZMs in vortices of CaKFe₄As₄, impurity-assisted vortices of LiFeAs, and quantum anomalous vortices in FeTe_0.55Se_0.45, illustrating the pathway of the developments of MZM research in IBSs. Finally, we give perspective on future experimental works in this field.

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Fundamental study towards a better understanding of low pressure radio-frequency plasmas for industrial applications

Yong-Xin Liu(刘永新), Quan-Zhi Zhang(张权治), Kai Zhao(赵凯), Yu-Ru Zhang(张钰如), Fei Gao(高飞),Yuan-Hong Song(宋远红), and You-Nian Wang(王友年)

2022 (8): 85202-085202. doi: 10.1088/1674-1056/ac7551

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Two classic radio-frequency (RF) plasmas, i.e., the capacitively and the inductively coupled plasmas (CCP and ICP), are widely employed in material processing, e.g., etching and thin film deposition, etc. Since RF plasmas are usually operated in particular circumstances, e.g., low pressures (mTorr-Torr), high-frequency electric field (13.56 MHz-200 MHz), reactive feedstock gases, diverse reactor configurations, etc., a variety of physical phenomena, e.g., electron resonance heating, discharge mode transitions, striated structures, standing wave effects, etc., arise. These physical effects could significantly influence plasma-based material processing. Therefore, understanding the fundamental processes of RF plasma is not only of fundamental interest, but also of practical significance for the improvement of the performance of the plasma sources. In this article, we review the major progresses that have been achieved in the fundamental study on the RF plasmas, and the topics include 1) electron heating mechanism, 2) plasma operation mode, 3) pulse modulated plasma, and 4) electromagnetic effects. These topics cover the typical issues in RF plasma field, ranging from fundamental to application.

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Mottness, phase string, and high-T_c superconductivity

Jing-Yu Zhao(赵靖宇) and Zheng-Yu Weng(翁征宇)

2022 (8): 87104-087104. doi: 10.1088/1674-1056/ac7a14

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It is a great discovery in physics of the twentieth century that the elementary particles in nature are dictated by gauge forces, characterized by a nonintegrable phase factor that an elementary particle of charge $q$ acquires from $A$ to $B$ points: $P \exp \left( \text{i} \frac q {\hbar c}\int_A^B A_{\mu}\text{d} x^{\mu}\right),$ where $A_{\mu}$ is the gauge potential and $P$ stands for path ordering. In a many-body system of strongly correlated electrons, if the so-called Mott gap is opened up by interaction, the corresponding Hilbert space will be fundamentally changed. A novel nonintegrable phase factor known as phase-string will appear and replace the conventional Fermi statistics to dictate the low-lying physics. Protected by the Mott gap, which is clearly identified in the high-$T_{\rm c}$ cuprate with a magnitude $> 1.5$ eV, such a singular phase factor can enforce a fractionalization of the electrons, leading to a dual world of exotic elementary particles with a topological gauge structure. A non-Fermi-liquid "parent" state will emerge, in which the gapless Landau quasiparticle is only partially robust around the so-called Fermi arc regions, while the main dynamics are dominated by two types of gapped spinons. Antiferromagnetism, superconductivity, and a Fermi liquid with full Fermi surface can be regarded as the low-temperature instabilities of this new parent state. Both numerics and experiments provide direct evidence for such an emergent physics of the Mottness, which lies in the core of a high-$T_{\rm c}$ superconducting mechanism.

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Recent advances of defect-induced spin and valley polarized states in graphene

Yu Zhang(张钰), Liangguang Jia(贾亮广), Yaoyao Chen(陈瑶瑶), Lin He(何林), and Yeliang Wang(王业亮)

2022 (8): 87301-087301. doi: 10.1088/1674-1056/ac70c4

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Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling, which can support a series of broken symmetry states. Atomic-scale defects in graphene are expected to lift these degenerate degrees of freedom at the nanoscale, and hence, lead to rich quantum states, highlighting promising directions for spintronics and valleytronics. In this article, we mainly review the recent scanning tunneling microscopy (STM) advances on the spin and/or valley polarized states induced by an individual atomic-scale defect in graphene, including a single-carbon vacancy, a nitrogen-atom dopant, and a hydrogen-atom chemisorption. Lastly, we give a perspective in this field.

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Magnetic van der Waals materials: Synthesis, structure, magnetism, and their potential applications

Zhongchong Lin(林中冲), Yuxuan Peng(彭宇轩), Baochun Wu(吴葆春), Changsheng Wang(王常生), Zhaochu Luo(罗昭初), and Jinbo Yang(杨金波)

2022 (8): 87506-087506. doi: 10.1088/1674-1056/ac6eed

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As the family of magnetic materials is rapidly growing, two-dimensional (2D) van der Waals (vdW) magnets have attracted increasing attention as a platform to explore fundamental physical problems of magnetism and their potential applications. This paper reviews the recent progress on emergent vdW magnetic compounds and their potential applications in devices. First, we summarize the current vdW magnetic materials and their synthetic methods. Then, we focus on their structure and the modulation of magnetic properties by analyzing the representative vdW magnetic materials with different magnetic structures. In addition, we pay attention to the heterostructures of vdW magnetic materials, which are expected to produce revolutionary applications of magnetism-related devices. To motivate the researchers in this area, we finally provide the challenges and outlook on 2D vdW magnetism.

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Progress and challenges in magnetic skyrmionics

Haifeng Du(杜海峰) and Xiangrong Wang(王向荣)

2022 (8): 87507-087507. doi: 10.1088/1674-1056/ac754f

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Magnetic skyrmions are two-dimensional localized topological spin-structures characterized by the skyrmion number that measures the number of times of spins wrapping the Bloch sphere. Skyrmions behave like particles under an external stimulus and are promising information carriers. Skyrmions can exist as an isolated object as well as skyrmion condensates in crystal structures, helical/conical states, mazes or irregular stripy states with emergent electromagnetic fields. Thus, skyrmions provide a nice platform for studying fundamental physics, other than its applications in spintronics. In this perspective, we briefly review some recent progress in the field and present an outlook of the fundamental challenges in device applications.

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Photon-interactions with perovskite oxides

Hongbao Yao(姚洪宝), Er-Jia Guo(郭尔佳), Chen Ge(葛琛), Can Wang(王灿), Guozhen Yang(杨国桢), and Kuijuan Jin(金奎娟)

2022 (8): 88106-088106. doi: 10.1088/1674-1056/ac754c

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Photons with variable energy, high coherency, and switchable polarization provide an ideal tool-kits for exploring the cutting-edge scientific questions in the condensed matter physics and material sciences. Over decades, extensive researches in the sample fabrication and excitation have employed the photon as one of the important means to synthesize and explore the low-dimensional quantum materials. In this review, we firstly summarize the recent progresses of the state-of-the-art thin-film deposition methods using excimer pulsed laser, by which syntactic oxides with atomic-unit-cell-thick layers and extremely high crystalline quality can be programmatically fabricated. We demonstrate that the artificially engineered oxide quantum heterostructures exhibit the unexpected physical properties which are absent in their parent forms. Secondly, we highlight the recent work on probing the symmetry breaking at the surface/interface/interior and weak couplings among nanoscale ferroelectric domains using optical second harmonic generation. We clarify the current challenges in the in-situ characterizations under the external fields and large-scale imaging using optical second harmonic generation. The improvements in the sample quality and the non-contact detection technique further promote the understanding of the mechanism of the novel properties emerged at the interface and inspire the potential applications, such as the ferroelectric resistive memory and ultrahigh energy storage capacitors.

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Evolution of electrical conductivity and semiconductor to metal transition of iron oxides at extreme conditions

Yukai Zhuang(庄毓凯) and Qingyang Hu(胡清扬)

2022 (8): 89101-089101. doi: 10.1088/1674-1056/ac7557

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Iron oxides are widely found as ores in Earth's crust and are also important constituents of its interiors. Their polymorphism, composition changes, and electronic structures play essential roles in controlling the structure and geodynamic properties of the solid Earth. While all-natural occurring iron oxides are semiconductors or insulators at ambient pressure, they start to metalize under pressure. Here in this work, we review the electronic conductivity and metallization of iron oxides under high-pressure conditions found in Earth's lower mantle. We summarize that the metallization of iron oxides is generally controlled by the pressure-induced bandgap closure near the Fermi level. After metallization, they possess much higher electrical and thermal conductivity, which will facilitate the thermal convection, support a more stable and thicker D^{$\prime\prime$} layer, and formulate Earth's magnetic field, all of which will constrain the large-scale dynamos of the mantle and core.

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Collisionless magnetic reconnection in the magnetosphere

Quanming Lu(陆全明), Huishan Fu(符慧山), Rongsheng Wang(王荣生), and San Lu(卢三)

2022 (8): 89401-089401. doi: 10.1088/1674-1056/ac76ab

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Magnetic reconnection underlies the physical mechanism of explosive phenomena in the solar atmosphere and planetary magnetospheres, where plasma is usually collisionless. In the standard model of collisionless magnetic reconnection, the diffusion region consists of two substructures: an electron diffusion region is embedded in an ion diffusion region, in which their scales are based on the electron and ion inertial lengths. In the ion diffusion region, ions are unfrozen in the magnetic fields while electrons are magnetized. The resulted Hall effect from the different motions between ions and electrons leads to the production of the in-plane currents, and then generates the quadrupolar structure of out-of-plane magnetic field. In the electron diffusion region, even electrons become unfrozen in the magnetic fields, and the reconnection electric field is contributed by the off-diagonal electron pressure terms in the generalized Ohm's law. The reconnection rate is insensitive to the specific mechanism to break the frozen-in condition, and is on the order of 0.1. In recent years, the launching of Cluster, THEMIS, MMS, and other spacecraft has provided us opportunities to study collisionless magnetic reconnection in the Earth's magnetosphere, and to verify and extend more insights on the standard model of collisionless magnetic reconnection. In this paper, we will review what we have learned beyond the standard model with the help of observations from these spacecraft as well as kinetic simulations.

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New experimental measurement of ^natSe(n, γ) cross section between 1 eV to 1 keV at the CSNS Back-n facility

Xin-Rong Hu(胡新荣), Long-Xiang Liu(刘龙祥), Wei Jiang(蒋伟), Jie Ren(任杰), Gong-Tao Fan(范功涛), Hong-Wei Wang(王宏伟), Xi-Guang Cao(曹喜光), Long-Long Song(宋龙龙), Ying-Du Liu(刘应都), Yue Zhang(张岳), Xin-Xiang Li(李鑫祥), Zi-Rui Hao(郝子锐), Pan Kuang(匡攀), Xiao-He Wang(王小鹤), Ji-Feng Hu(胡继峰), Bing Jiang(姜炳), De-Xin Wang(王德鑫), Suyalatu Zhang(张苏雅拉吐), Zhen-Dong An(安振东), Yu-Ting Wang(王玉廷), Chun-Wang Ma(马春旺), Jian-Jun He(何建军), Jun Su(苏俊), Li-Yong Zhang(张立勇), Yu-Xuan Yang(杨宇萱), Sheng Jin(金晟), and Kai-Jie Chen(陈开杰)

2022 (8): 80101-080101. doi: 10.1088/1674-1056/ac6ee2

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The ⁷⁴Se is one of 35 p-nuclei, and ⁸²Se is a r-process only nucleus, and their (n, γ) cross sections are vital input parameters for nuclear astrophysics reaction network calculations. The neutron capture cross section in the resonance range of isotopes and even natural selenium samples has not been measured. Prompt γ-rays originating from neutron-induced capture events were detected by four C₆D₆ liquid scintillator detectors at the Back-n facility of China Spallation Neutron Source (CSNS). The pulse height weighting technique (PHWT) was used to analyze the data in the 1 eV to 100 keV region. The deduced neutron capture cross section was compared with ENDF/B-VIII.0, JEFF-3.2, and JENDL-4.0, and some differences were found. Resonance parameters were extracted by the R-matrix code SAMMY in the 1 eV-1 keV region. All the cross sections of ^natSe and resonance parameters are given in the datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00019.

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Relativistic calculations on the transition electric dipole moments and radiative lifetimes of the spin-forbidden transitions in the antimony hydride molecule

Yong Liu(刘勇), Lu-Lu Li(李露露), Li-Dan Xiao(肖利丹), and Bing Yan(闫冰)

2022 (8): 83101-083101. doi: 10.1088/1674-1056/ac6ee1

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Calculations on the spectroscopic constants and transition properties of the first three states (${\rm a}^{1}\Delta $, ${\rm b}^{1}\Sigma^{+}$, and X$^{3}\Sigma^-$) of the SbH molecule were performed under the relativistic framework using the exact two-component Hamiltonian (X2C). The potential energy curves in the Franck-Condon region were computed and compared with the previous values. Furthermore, the transition dipole moments for the weak spin-forbidden transitions (${\rm b}0^{+}$-X$_{1}0^{+}$, ${\rm b}0^{+}$-X$_{2}$1, X$_{1}0^{+}$-X$_{2}$1, and X$_{2}$1-${\rm a}$2) were reported. The spontaneous radiative lifetime of the ${\rm b}^{1}\Sigma^{+}$ ($\upsilon '=0$) state was calculated as 163.5 $\pm$ 7.5 μs, which is in reasonable agreement with the latest experimental value of 173 $\pm$ 3 μs. The spontaneous radiative lifetimes of the X$_{2}$1 ($\upsilon '=0$) state and the ${\rm a}$2 ($\upsilon '=0$) state were calculated to be 48.6 s and $\sim 8 $ ms, respectively. Our study is expected to be a benchmark transition property computation for comparison with other theoretical and experimental results. The datasets presented in this paper, including the transition dipole moments, are openly available at https://dx.doi.org/10.11922/sciencedb.j00113.00018.

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Integral cross sections for electron impact excitations of argon and carbon dioxide

Shu-Xing Wang(汪书兴) and Lin-Fan Zhu(朱林繁)

2022 (8): 83401-083401. doi: 10.1088/1674-1056/ac6336

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Electron-impact excitation integral cross sections play an important role in understanding the energy transfer processes in many applied physics. Practical applications require integral cross sections in a wide collision energy range from the excitation threshold to several keV. The recently developed BE-scaling method is able to meet the demands of integral cross sections for dipole-allowed transitions while the prerequisite relies on the accurate generalized oscillator strengths. Fast electron and x-ray scatterings are the conventional experimental techniques to approach the generalized oscillator strengths, and the joint study by both methods can provide credible cross-checks. The validated generalized oscillator strengths can then be used to extrapolate optical oscillator strengths by fitting the data with the Lassettre formula. The fitted curve also enables the integration of generalized oscillator strengths over the whole momentum transfer region to obtain the BE-scaled integral excitation cross sections. Here, experimental measurements by both fast electron and x-ray scattering of argon and carbon dioxide are reviewed. The integral cross sections for some low-lying states are derived from the cross-checked generalized oscillator strengths for the first time. The integral cross sections presented in this paper are openly available at https://doi.org/10.11922/sciencedb.01466.

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Magnetic properties of oxides and silicon single crystals

Zhong-Xue Huang(黄忠学), Rui Wang(王瑞), Xin Yang(杨鑫), Hao-Feng Chen(陈浩锋), and Li-Xin Cao(曹立新)

2022 (8): 87501-087501. doi: 10.1088/1674-1056/ac70c2

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The magnetic properties of single crystals Si, SrTiO₃, LaAlO₃, MgO, and (La,Sr)(Al,Ta)O₃ were investigated systematically. Three origins of the magnetizations of these crystals, namely, an intrinsic diamagnetic, a paramagnetic, and a ferromagnetic contribution, have been found to influence the magnetic signals measured on the crystals, in some important application scenarios such crystals being served as substrates with the magnetic thin film epitaxially grown on. Quantitative analyses methodologies were developed and thorough investigations were performed on the crystals with the intrinsic materials parameters thus revealed, especially that the intrinsic diamagnetic susceptibility differential dχ_dia/dT were identified quantitatively for the first time in SrTiO₃, LaAlO₃, MgO, and (La,Sr)(Al,Ta)O₃. The paramagnetic contribution is found to be the key in terms of the magnetic properties of the crystals, which in turn is in fact a consequence of the 3d impurities doping inside the crystal. All the intrinsic materials parameters are given in this paper as datasets, the datasets are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00028.

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A 658-W VCSEL-pumped rod laser module with 52.6% optical efficiency

Xue-Peng Li(李雪鹏), Jing Yang(杨晶), Meng-Shuo Zhang(张梦硕), Tian-Li Yang(杨天利), Xiao-Jun Wang(王小军), and Qin-Jun Peng(彭钦军)

2022 (8): 84207-084207. doi: 10.1088/1674-1056/ac728f

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A high-efficiency and high-power vertical-cavity surface-emitting laser (VCSEL) side-pumped rod Nd:YAG laser with temperature adaptability are demonstrated. The VCSEL side-pumped laser module is designed and optimized. Five VCSEL arrays are symmetrically located around the laser rod and a large size diffused reflection chamber is designed to ensure a uniform pump distribution. Furthermore, the absorbed pump power distribution of the rod is simulated to verify the uniformity of the pump absorption. Finally, a proof-of-principle experiment is performed in short linear cavity laser with single laser module. A continuous-wave output power of 658 W at 1064 nm is obtained, the corresponding optical-to-optical efficiency is 52.6%, and the power variations are ±0.7% over 400 s and ±3.1% over the temperature range from 16 ℃ to 26 ℃. To the best of our knowledge, this is the highest output power and the highest optical-to-optical efficiency ever reported for VCSEL pumped solid-state lasers. By inserting a telescopic module into the cavity and optimizing the TEM₀₀ mode volume, the average beam quality is measured to be M²=1.34 under an output power of 102 W. The experimental results reveal that such a high power rod laser module with temperature stability is appropriate or field applications.

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Design and high-power test of 800-kW UHF klystron for CEPC

Ou-Zheng Xiao(肖欧正), Shigeki Fukuda, Zu-Sheng Zhou(周祖圣), Un-Nisa Zaib, Sheng-Chang Wang(王盛昌), Zhi-Jun Lu(陆志军), Guo-Xi Pei(裴国玺), Munawar Iqbal, and Dong Dong(董东)

2022 (8): 88401-088401. doi: 10.1088/1674-1056/ac6b26

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To reduce the energy demand and operation cost for circular electron positron collider (CEPC), the high efficiency klystrons are being developed at Institute of High Energy Physics, Chinese Academy of Sciences. A 800-kW continuous wave (CW) klystron operating at frequency of 650-MHz has been designed. The results of beam-wave interaction simulation with several different codes are presented. The efficiency is optimized to be 65% with a second harmonic cavity in three-dimensional (3D) particle-in-cell code CST. The effect of cavity frequency error and mismatch load on efficiency of klystron have been investigated. The design and cold test of reentrant cavities are described, which meet the requirements of RF section design. So far, the manufacturing and high-power test of the first klystron prototype have been completed. When the gun operated at DC voltage of 80 kV and current of 15.4 A, the klystron peak power reached 804 kW with output efficiency of about 65.3% at 40% duty cycle. The 1-dB bandwidth is ±0.8 MHZ. Due to the crack of ceramic window, the CW power achieved about 700 kW. The high-power test results are in good agreement with 3D simulation.

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Two-dimensional Sb cluster superlattice on Si substrate fabricated by a two-step method

Runxiao Zhang(张润潇), Zi Liu(刘姿), Xin Hu(胡昕), Kun Xie(谢鹍), Xinyue Li(李新月), Yumin Xia(夏玉敏), and Shengyong Qin(秦胜勇)

2022 (8): 86801-086801. doi: 10.1088/1674-1056/ac70c1

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Nanoclusters consisting of a few atoms have attracted a lot of research interests due to their exotic size-dependent properties. Here, well-ordered two-dimensional Sb cluster superlattice was fabricated on Si substrate by a two-step method and characterized by scanning tunneling microscopy. High resolution scanning tunneling microscope measurements revealed the fine structures of the Sb clusters, which consist of several Sb atoms ranging from 2 to 7. Furthermore, the electronic structure of the nanocluster displays the quantized energy-level which is due to the single-electron tunneling effects. We believe that the fabrication of Sb cluster superlattice broadens the species of the cluster superlattice and provides a promising candidate to further explore the novel physical and chemical properties of the semimetal nanocluster.

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Effect of f-c hybridization on the $\gamma\to \alpha$ phase transition of cerium studied by lanthanum doping

Yong-Huan Wang(王永欢), Yun Zhang(张云), Yu Liu(刘瑜), Xiao Tan(谈笑), Ce Ma(马策), Yue-Chao Wang(王越超), Qiang Zhang(张强), Deng-Peng Yuan(袁登鹏), Dan Jian(简单), Jian Wu(吴健), Chao Lai(赖超), Xi-Yang Wang(王西洋), Xue-Bing Luo(罗学兵), Qiu-Yun Chen(陈秋云), Wei Feng(冯卫), Qin Liu(刘琴), Qun-Qing Hao(郝群庆), Yi Liu(刘毅), Shi-Yong Tan(谭世勇), Xie-Gang Zhu(朱燮刚), Hai-Feng Song(宋海峰), and Xin-Chun Lai(赖新春)

2022 (8): 87102-087102. doi: 10.1088/1674-1056/ac7210

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The hybridization between the localized 4f level (f) with conduction (c) electrons in $\gamma $-Ce upon cooling has been previously revealed in single crystalline thin films experimentally and theoretically, whereas its influence on the $\gamma \to \alpha $ phase transition was not explicitly verified, due to the fact that the phase transition happened in the bulk-layer, leaving the surface in the $\gamma $ phase. Here in our work, we circumvent this issue by investigating the effect of alloying addition of La on Ce, by means of crystal structure, electronic transport and angle resolved photoemission spectroscopy measurements, together with a phenomenological periodic Anderson model and a modified Anderson impurity model. Our current researches indicate that the weakening of f-c hybridization is the major factor in the suppression of $\gamma \to \alpha $ phase transition by La doping. The consistency of our results with the effects of other rare earth and actinide alloying additions on the $\gamma \to \alpha $ phase transition of Ce is also discussed. Our work demonstrates the importance of the interaction between f and c electrons in understanding the unconventional phase transition in Ce, which is intuitive for further researches on other rare earth and actinide metals and alloys with similar phase transition behaviors.

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Precisely controlling the twist angle of epitaxial MoS₂/graphene heterostructure by AFM tip manipulation

Jiahao Yuan(袁嘉浩), Mengzhou Liao(廖梦舟), Zhiheng Huang(黄智恒), Jinpeng Tian(田金朋), Yanbang Chu(褚衍邦), Luojun Du(杜罗军), Wei Yang(杨威), Dongxia Shi(时东霞), Rong Yang(杨蓉), and Guangyu Zhang(张广宇)

2022 (8): 87302-087302. doi: 10.1088/1674-1056/ac720e

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Two-dimensional (2D) moiré materials have attracted a lot of attention and opened a new research frontier of twistronics due to their novel physical properties. Although great progress has been achieved, the inability to precisely and reproducibly manipulate the twist angle hinders the further development of twistronics. Here, we demonstrated an atomic force microscope (AFM) tip manipulation method to control the interlayer twist angle of epitaxial MoS₂/graphene heterostructure with an ultra-high accuracy better than 0.1°. Furthermore, conductive AFM and spectroscopic characterizations were conducted to show the effects of the twist angle on moiré pattern wavelength, phonons and excitons. Our work provides a technique to precisely control the twist angle of 2D moiré materials, enabling the possibility to establish the phase diagrams of moiré physics with twist angle.

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Conservation of the particle-hole symmetry in the pseudogap state in optimally-doped Bi₂Sr₂CuO_6+δ superconductor

Hongtao Yan(闫宏涛), Qiang Gao(高强), Chunyao Song(宋春尧), Chaohui Yin(殷超辉), Yiwen Chen(陈逸雯), Fengfeng Zhang(张丰丰), Feng Yang(杨峰), Shenjin Zhang(张申金), Qinjun Peng(彭钦军), Guodong Liu(刘国东), Lin Zhao(赵林), Zuyan Xu(许祖彦), and X. J. Zhou(周兴江)

2022 (8): 87401-087401. doi: 10.1088/1674-1056/ac7214

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The pseudogap state is one of the most enigmatic characteristics in the anomalous normal state properties of the high temperature cuprate superconductors. A central issue is to reveal whether there is a symmetry breaking and which symmetries are broken across the pseudogap transition. By performing high resolution laser-based angle-resolved photoemission measurements on the optimally-doped Bi₂Sr_1.6La_0.4CuO_6+δ superconductor, we report the observations of the particle-hole symmetry conservation in both the superconducting state and the pseudogap state along the entire Fermi surface. These results provide key insights in understanding the nature of the pseudogap and its relation with high temperature superconductivity.

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Monolayer MoS₂ of high mobility grown on SiO₂ substrate by two-step chemical vapor deposition

Jia-Jun Ma(马佳俊), Kang Wu(吴康), Zhen-Yu Wang(王振宇), Rui-Song Ma(马瑞松), Li-Hong Bao(鲍丽宏), Qing Dai(戴庆), Jin-Dong Ren(任金东), and Hong-Jun Gao(高鸿钧)

2022 (8): 88105-088105. doi: 10.1088/1674-1056/ac6737

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We report a novel two-step ambient pressure chemical vapor deposition (CVD) pathway to grow high-quality MoS₂ monolayer on the SiO₂ substrate with large crystal size up to 110 μm. The large specific surface area of the pre-synthesized MoO₃ flakes on the mica substrate compared to MoO₃ powder could dramatically reduce the consumption of the Mo source. The electronic information inferred from the four-probe scanning tunneling microscope (4P-STM) image explains the threshold voltage variations and the n-type behavior observed in the two-terminal transport measurements. Furthermore, the direct van der Pauw transport also confirms its relatively high carrier mobility. Our study provides a reliable method to synthesize high-quality MoS₂ monolayer, which is confirmed by the direct 4P-STM measurement results. Such methodology is a key step toward the large-scale growth of transition metal dichalcogenides (TMDs) on the SiO₂ substrate and is essential to further development of the TMDs-related integrated devices.

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Robustness measurement of scale-free networks based on motif entropy

Yun-Yun Yang(杨云云), Biao Feng(冯彪), Liao Zhang(张辽), Shu-Hong Xue(薛舒红), Xin-Lin Xie(谢新林), and Jian-Rong Wang(王建荣)

2022 (8): 80201-080201. doi: 10.1088/1674-1056/ac6942

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As a classical complex network model, scale-free network is widely used and studied. And motifs, as a high-order subgraph structure, frequently appear in scale-free networks, and have a great influence on the structural integrity, functional integrity and dynamics of the networks. In order to overcome the shortcomings in the existing work on the robustness of complex networks, only nodes or edges are considered, while the defects of high-order structure in the network are ignored. From the perspective of network motif, we propose an entropy of node degree distribution based on motif to measure the robustness of scale-free networks under random attacks. The effectiveness and superiority of our method are verified and analyzed in the BA scale-free networks.

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Quantum fields presentation and generating functions of symplectic Schur functions and symplectic universal characters

Denghui Li(李登慧), Fei Wang(王菲), and Zhaowen Yan(颜昭雯)

2022 (8): 80202-080202. doi: 10.1088/1674-1056/ac4f57

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This paper is concerned with construction of quantum fields presentation and generating functions of symplectic Schur functions and symplectic universal characters. The boson-fermion correspondence for these symmetric functions have been presented. In virtue of quantum fields, we derive a series of infinite order nonlinear integrable equations, namely, universal character hierarchy, symplectic KP hierarchy and symplectic universal character hierarchy, respectively. In addition, the solutions of these integrable systems have been discussed.

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Green's function Monte Carlo method combined with restricted Boltzmann machine approach to the frustrated J₁-J₂ Heisenberg model

He-Yu Lin(林赫羽), Rong-Qiang He(贺荣强), and Zhong-Yi Lu(卢仲毅)

2022 (8): 80203-080203. doi: 10.1088/1674-1056/ac615f

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Restricted Boltzmann machine (RBM) has been proposed as a powerful variational ansatz to represent the ground state of a given quantum many-body system. On the other hand, as a shallow neural network, it is found that the RBM is still hardly able to capture the characteristics of systems with large sizes or complicated interactions. In order to find a way out of the dilemma, here, we propose to adopt the Green's function Monte Carlo (GFMC) method for which the RBM is used as a guiding wave function. To demonstrate the implementation and effectiveness of the proposal, we have applied the proposal to study the frustrated J₁-J₂ Heisenberg model on a square lattice, which is considered as a typical model with sign problem for quantum Monte Carlo simulations. The calculation results demonstrate that the GFMC method can significantly further reduce the relative error of the ground-state energy on the basis of the RBM variational results. This encourages to combine the GFMC method with other neural networks like convolutional neural networks for dealing with more models with sign problem in the future.

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Evolution of donations on scale-free networks during a COVID-19 breakout

Xian-Jia Wang(王先甲) and Lin-Lin Wang(王琳琳)

2022 (8): 80204-080204. doi: 10.1088/1674-1056/ac4651

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Having a large number of timely donations during the early stages of a COVID-19 breakout would normally be considered rare. Donation is a special public goods game with zero yield for donors, and it has the characteristics of the prisoners' dilemma. This paper discusses why timely donations in the early stages of COVID-19 occurred. Based on the idea that donation is a strategy adopted by players during interconnection on account of their understanding of the environment, donation-related populations are placed on social networks and the inter-correlation structures in the population are described by scale-free networks. Players in donation-related populations are of four types: donors, illegal beneficiaries, legal beneficiaries, and inactive people. We model the evolutionary game of donation on a scale-free network. Donors, illegal beneficiaries and inactive people learn and update strategies under the Fermi update rule, whereas the conversion between legal beneficiaries and the other three types is determined by the environment surrounding the players. We study the evolution of cooperative action when the agglomeration coefficient, the parameters of the utility function, the noise intensity, the utility coefficient, the donation coefficient and the initial states of the population on the scale-free network change. For population sizes of 50, 100, 150, and 200, we give the utility functions and the agglomeration coefficients for promoting cooperation and study the corresponding steady states and structural characteristics of the population. We identify the best ranges of the noise intensity K, the donation coefficient α and the utility coefficient β for promoting cooperation at different population sizes. Furthermore, with the increase of the population size, the donor traps are found. At the same time, it is discovered that the initial states of the population have a great impact on the steady states; thus the upper and lower triangle phenomena are proposed. We also find that the population size itself is also an important factor for promoting donation, pointing out the direction of efforts to further promote donation and achieve better social homeostasis under the donation model.

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Hard-core Hall tube in superconducting circuits

Xin Guan(关欣), Gang Chen(陈刚), Jing Pan(潘婧), and Zhi-Guo Gui(桂志国)

2022 (8): 80302-080302. doi: 10.1088/1674-1056/ac633b

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The Hall tube as a minimum model to simulate the integer quantum Hall effect is essential for exploring topological physics, while it has not been constructed in the recent developing successfully experiments on superconducting circuits. In this work, we propose a feasible experiment scheme using three legs superconducting circuits with transmon qubits to realize a Hall tube. Then we first investigate its topological properties. Since the time-reversal, particle-hole, and chiral symmetries are all broken for the system, the Hall tube belongs to the A class of the Altland-Zirnbauer classification. We obtain the corresponding topological phase transition both numerically and analytically. Since the chirality is a key character of the quantum Hall effect, we secondly investigate the chiral physics in the Hall tube. We find the topological protected chiral edge currents and discuss its robustness. Finally, we give the possible experimental observations of the topological state and topological protected chiral edge currents.

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Finite-key analysis of practical time-bin high-dimensional quantum key distribution with afterpulse effect

Yu Zhou(周雨), Chun Zhou(周淳), Yang Wang(汪洋), Yi-Fei Lu(陆宜飞), Mu-Sheng Jiang(江木生), Xiao-Xu Zhang(张晓旭), and Wan-Su Bao(鲍皖苏)

2022 (8): 80303-080303. doi: 10.1088/1674-1056/ac6017

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High-dimensional quantum resources provide the ability to encode several bits of information on a single photon, which can particularly increase the secret key rate rate of quantum key distribution (QKD) systems. Recently, a practical four-dimensional QKD scheme based on time-bin quantum photonic state, only with two single-photon avalanche detectors as measurement setup, has been proven to have a superior performance than the qubit-based one. In this paper, we extend the results to our proposed eight-dimensional scheme. Then, we consider two main practical factors to improve its secret key bound. Concretely, we take the afterpulse effect into account and apply a finite-key analysis with the intensity fluctuations. Our secret bounds give consideration to both the intensity fluctuations and the afterpulse effect for the high-dimensional QKD systems. Numerical simulations show the bound of eight-dimensional QKD scheme is more robust to the intensity fluctuations but more sensitive to the afterpulse effect than the four-dimensional one.

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Purification in entanglement distribution with deep quantum neural network

Jin Xu(徐瑾), Xiaoguang Chen(陈晓光), Rong Zhang(张蓉), and Hanwei Xiao(肖晗微)

2022 (8): 80304-080304. doi: 10.1088/1674-1056/ac6330

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Entanglement distribution is important in quantum communication. Since there is no information with value in this process, purification is a good choice to solve channel noise. In this paper, we simulate the purification circuit under true environment on Cirq, which is a noisy intermediate-scale quantum (NISQ) platform. Besides, we apply quantum neural network (QNN) to the state after purification. We find that combining purification and quantum neural network has good robustness towards quantum noise. After general purification, quantum neural network can improve fidelity significantly without consuming extra states. It also helps to obtain the advantage of entangled states with higher dimension under amplitude damping noise. Thus, the combination can bring further benefits to purification in entanglement distribution.

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Non-universal Fermi polaron in quasi two-dimensional quantum gases

Yue-Ran Shi(石悦然), Jin-Ge Chen(陈金鸽), Kui-Yi Gao(高奎意), and Wei Zhang(张威)

2022 (8): 80305-080305. doi: 10.1088/1674-1056/ac4cb9

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We consider an impurity problem in a quasi-two-dimensional Fermi gas, where a spin-down impurity is immersed in a Fermi sea of N spin-up atoms. Using a variational approach and an effective two-channel model, we obtain the energy for a wide range of interaction strength and for various different mass ratios between the impurity and the background fermion in the context of heteronuclear mixture. We demonstrate that in a quasi-two-dimensional Fermi gas there exists a transition of the ground state from polaron in the weakly interacting region to molecule in the strongly interacting region. The critical interaction strength of the polaron-molecule transition is non-universal and depends on the particle density of the background Fermi sea. We also investigate the excited repulsive polaron state, and find similar non-universal behavior.

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Achieving ultracold Bose-Fermi mixture of ⁸⁷Rb and ⁴⁰K with dual dark magnetic-optical-trap

Jie Miao(苗杰), Guoqi Bian(边国旗), Biao Shan(单标), Liangchao Chen(陈良超), Zengming Meng(孟增明), Pengjun Wang(王鹏军), Lianghui Huang(黄良辉), and Jing Zhang(张靖)

2022 (8): 80306-080306. doi: 10.1088/1674-1056/ac5882

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We demonstrate that dual dark magnetic-optical-traps (MOTs) have great importance in the two-species ⁸⁷Rb and ⁴⁰K mixture compared with dual bright MOTs. The dark MOT has a little improvement in the trapping of single-species ⁸⁷Rb or ⁴⁰K gases compared with bright MOT. For the case of loading two-species ⁸⁷Rb and ⁴⁰K simultaneously, the improvement of ⁴⁰K in the dual dark MOTs is mainly from the reduction of light-assisted collision losses. The dual dark MOTs employ a pair of conical lenses to produce the hollow beam for repump laser with high efficiency. The number and density of ⁸⁷Rb and ⁴⁰K atoms after evaporative cooling in the hybrid magnetic trap with dark MOT loading are compared with those in bright MOT. The atoms with large number and high density make it easier to realize the quantum degenerate of Bose-Fermi mixture.

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Direct measurement of two-qubit phononic entangled states via optomechanical interactions

A-Peng Liu(刘阿鹏), Liu-Yong Cheng(程留永), Qi Guo(郭奇), Shi-Lei Su(苏石磊), Hong-Fu Wang(王洪福), and Shou Zhang(张寿)

2022 (8): 80307-080307. doi: 10.1088/1674-1056/ac5d2f

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We propose schemes of direct concurrence measurement for two-qubit phononic states from quantized mechanical vibration. By combining the Mach-Zehnder interferometer with the optomechanical cross-Kerr nonlinear effect, direct concurrence measurement schemes for two-qubit phononic entangled states are achieved with the help of photon detection with respect to the output of the interferometer. For different types of entangled states, diversified quantum devices and operations are designed accordingly. The final analysis shows reasonable performance under the current parameter conditions. Our schemes may be useful for potential phonon-based quantum computation and information in the future.

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Inertial focusing and rotating characteristics of elliptical and rectangular particle pairs in channel flow

Pei-Feng Lin(林培锋), Xiao Hu(胡箫), and Jian-Zhong Lin(林建忠)

2022 (8): 80501-080501. doi: 10.1088/1674-1056/ac5983

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The lattice Boltzmann method is used to study the inertial focusing and rotating characteristics of two-dimensional elliptical particles and rectangular particles in channel flow. The results show that both elliptical particles and rectangular particles initially located on one side and two sides of channel centerline migrate first towards the equilibrium position. Then, the single-line particle train with an increasing spacing and the staggered particle train with stable spacing are formed. The axial spacing of the staggered particle pair increases with aspect ratio and Reynolds number increasing. The staggered elliptical or rectangular particle pairs form perpendicular orientation angles, which will be more obvious at larger aspect ratio and lower Reynolds number. The single-line particle trains with different shapes seldom form the perpendicular orientation angle.

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Characteristics of piecewise linear symmetric tri-stable stochastic resonance system and its application under different noises

Gang Zhang(张刚), Yu-Jie Zeng(曾玉洁), and Zhong-Jun Jiang(蒋忠均)

2022 (8): 80502-080502. doi: 10.1088/1674-1056/ac588b

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Weak signal detection has become an important means of mechanical fault detections. In order to solve the problem of poor signal detection performance in classical tristable stochastic resonance system (CTSR), a novel unsaturated piecewise linear symmetric tristable stochastic resonance system (PLSTSR) is proposed. Firstly, by making the analysis and comparison of the output and input relationship between CTSR and PLSTSR, it is verified that the PLSTSR has good unsaturation characteristics. Then, on the basis of adiabatic approximation theory, the Kramers escape rate, the mean first-passage time (MFPT), and output signal-to-noise ratio (SNR) of PLSTSR are deduced, and the influences of different system parameters on them are studied. Combined with the adaptive genetic algorithm to synergistically optimize the system parameters, the PLSTSR and CTSR are used for numerically simulating the verification and detection of low-frequency, high-frequency, and multi-frequency signals. And the results show that the SNR and output amplitude of the PLSTSR are greatly improved compared with those of the CTSR, and the detection effect is better. Finally, the PLSTSR and CTSR are applied to the bearing fault detection under Gaussian white noise and Levy noise. The experimental results also show that the PLSTSR can obtain larger output amplitude and SNR, and can detect fault signals more easily, which proves that the system has better performance than other systems in bearing fault detection, and has good theoretical significance and practical value.

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Hyperparameter on-line learning of stochastic resonance based threshold networks

Weijin Li(李伟进), Yuhao Ren(任昱昊), and Fabing Duan(段法兵)

2022 (8): 80503-080503. doi: 10.1088/1674-1056/ac5886

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Aiming at training the feed-forward threshold neural network consisting of nondifferentiable activation functions, the approach of noise injection forms a stochastic resonance based threshold network that can be optimized by various gradient-based optimizers. The introduction of injected noise extends the noise level into the parameter space of the designed threshold network, but leads to a highly non-convex optimization landscape of the loss function. Thus, the hyperparameter on-line learning procedure with respective to network weights and noise levels becomes of challenge. It is shown that the Adam optimizer, as an adaptive variant of stochastic gradient descent, manifests its superior learning ability in training the stochastic resonance based threshold network effectively. Experimental results demonstrate the significant improvement of performance of the designed threshold network trained by the Adam optimizer for function approximation and image classification.

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Synchronously scrambled diffuse image encryption method based on a new cosine chaotic map

Xiaopeng Yan(闫晓鹏), Xingyuan Wang(王兴元), and Yongjin Xian(咸永锦)

2022 (8): 80504-080504. doi: 10.1088/1674-1056/ac5a43

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We present a new cosine chaotic mapping proved by chaos theory test and analysis such that the system has good cryptography properties, wide chaos range, simple structure, and good sensitivity to initial value, and the mapping can meet the needs of chaotic image encryption. Based on the cosine chaotic system, we propose a new encryption method. First, according to the cyclic characteristics of the mapping, the cyclic information wave is simulated. Second, the quasi-Doppler effect is used to synchronously scramble and diffuse the image to obfuscate the original pixel. Finally, the XOR diffusion of image pixels is carried out by information wave to further enhance the encryption effect. Simulation experiment and security analysis show that the algorithm has good security, can resist the common attack mode, and has good efficiency.

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Power-law statistics of synchronous transition in inhibitory neuronal networks

Lei Tao(陶蕾) and Sheng-Jun Wang(王圣军)

2022 (8): 80505-080505. doi: 10.1088/1674-1056/ac5c31

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We investigate the relationship between the synchronous transition and the power law behavior in spiking networks which are composed of inhibitory neurons and balanced by dc current. In the region of the synchronous transition, the avalanche size and duration distribution obey a power law distribution. We demonstrate the robustness of the power law for event sizes at different parameters and multiple time scales. Importantly, the exponent of the event size and duration distribution can satisfy the critical scaling relation. By changing the network structure parameters in the parameter region of transition, quasicriticality is observed, that is, critical exponents depart away from the criticality while still hold approximately to a dynamical scaling relation. The results suggest that power law statistics can emerge in networks composed of inhibitory neurons when the networks are balanced by external driving signal.

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Oscillation properties of matter-wave bright solitons in harmonic potentials

Shu-Wen Guan(关淑文), Ling-Zheng Meng(孟令正), and Li-Chen Zhao(赵立臣)

2022 (8): 80506-080506. doi: 10.1088/1674-1056/ac4e0f

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We investigate the oscillation periods of bright soliton pair or vector bright soliton pair in harmonic potentials. We demonstrate that periods of low-speed solitons are greatly affected by the position shift during their collisions. The modified oscillation periods are described by defining a characterized speed, with the aid of asymptotic analysis on related exact analytic soliton solutions in integrable cases. The oscillation period can be used to distinguish the inter- and intra-species interactions between solitons. However, a bright soliton cannot oscillate in a harmonic trap, when it is coupled with a dark soliton (without any trapping potentials). Interestingly, it can oscillate in an anti-harmonic potential, and the oscillation behavior is explained by a quasi-particle theory. The modified period of two dark-bright solitons can be also described well by the characterized speed. These results address well the effects of position shift during soliton collision, which provides an important supplement for previous studies without considering phase shift effects.

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Effect of astrocyte on synchronization of thermosensitive neuron-astrocyte minimum system

Yi-Xuan Shan(单仪萱), Hui-Lan Yang(杨惠兰), Hong-Bin Wang(王宏斌), Shuai Zhang(张帅), Ying Li(李颖), and Gui-Zhi Xu(徐桂芝)

2022 (8): 80507-080507. doi: 10.1088/1674-1056/ac490c

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Astrocytes have a regulatory function on the central nervous system (CNS), especially in the temperature-sensitive hippocampal region. In order to explore the thermosensitive dynamic mechanism of astrocytes in the CNS, we establish a neuron-astrocyte minimum system to analyze the synchronization change characteristics based on the Hodgkin-Huxley model, in which a pyramidal cell and an interneuron are connected by an astrocyte. The temperature range is set as 0 ℃-40 ℃ to juggle between theoretical calculation and the reality of a brain environment. It is shown that the synchronization of thermosensitive neurons exhibits nonlinear behavior with changes in astrocyte parameters. At a temperature range of 0 ℃-18 ℃, the effects of the astrocyte can provide a tremendous influence on neurons in synchronization. We find the existence of a value for inositol triphosphate (IP₃) production rate and feedback intensities of astrocytes to neurons, which can ensure the weak synchronization of two neurons. In addition, it is revealed that the regulation of astrocytes to pyramidal cells is more sensitive than that to interneurons. Finally, it is shown that the synchronization and phase transition of neurons depend on the change in Ca²⁺ concentration at the temperature of weak synchronization. The results in this paper provide some enlightenment on the mechanism of cognitive dysfunction and neurological disorders with astrocytes.

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Exponential sine chaotification model for enhancing chaos and its hardware implementation

Rui Wang(王蕊), Meng-Yang Li(李孟洋), and Hai-Jun Luo(罗海军)

2022 (8): 80508-080508. doi: 10.1088/1674-1056/ac6335

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Chaotic systems have been intensively studied for their roles in many applications, such as cryptography, secure communications, nonlinear controls, etc. However, the limited complexity of existing chaotic systems weakens chaos-based practical applications. Designing chaotic maps with high complexity is attractive. This paper proposes the exponential sine chaotification model (ESCM), a method of using the exponential sine function as a nonlinear transform model, to enhance the complexity of chaotic maps. To verify the performance of the ESCM, we firstly demonstrated it through theoretical analysis. Then, to exhibit the high efficiency and usability of ESCM, we applied ESCM to one-dimensional (1D) and multi-dimensional (MD) chaotic systems. The effects were examined by the Lyapunov exponent and it was found that enhanced chaotic maps have much more complicated dynamic behaviors compared to their originals. To validate the simplicity of ESCM in hardware implementation, we simulated three enhanced chaotic maps using a digital signal processor (DSP). To explore the ESCM in practical application, we applied ESCM to image encryption. The results verified that the ESCM can make previous chaos maps competitive for usage in image encryption.

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Ionospheric vertical total electron content prediction model in low-latitude regions based on long short-term memory neural network

Tong-Bao Zhang(张同宝), Hui-Jian Liang(梁慧剑),Shi-Guang Wang(王时光), and Chen-Guang Ouyang(欧阳晨光)

2022 (8): 80701-080701. doi: 10.1088/1674-1056/ac4487

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Ionosphere delay is one of the main sources of noise affecting global navigation satellite systems, operation of radio detection and ranging systems and very-long-baseline-interferometry. One of the most important and common methods to reduce this phase delay is to establish accurate nowcasting and forecasting ionospheric total electron content models. For forecasting models, compared to mid-to-high latitudes, at low latitudes, an active ionosphere leads to extreme differences between long-term prediction models and the actual state of the ionosphere. To solve the problem of low accuracy for long-term prediction models at low latitudes, this article provides a low-latitude, long-term ionospheric prediction model based on a multi-input-multi-output, long-short-term memory neural network. To verify the feasibility of the model, we first made predictions of the vertical total electron content data 24 and 48 hours in advance for each day of July 2020 and then compared both the predictions corresponding to a given day, for all days. Furthermore, in the model modification part, we selected historical data from June 2020 for the validation set, determined a large offset from the results that were predicted to be active, and used the ratio of the mean absolute error of the detected results to that of the predicted results as a correction coefficient to modify our multi-input-multi-output long short-term memory model. The average root mean square error of the 24-hour-advance predictions of our modified model was 4.4 TECU, which was lower and better than 5.1 TECU of the multi-input-multi-output, long short-term memory model and 5.9 TECU of the IRI-2016 model.

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Dynamic polarizabilities of the clock states of Al⁺

Yuan-Fei Wei(魏远飞), Zhi-Ming Tang(唐志明), Cheng-Bin Li(李承斌), Yang Yang(杨洋), Ya-Ming Zou(邹亚明), Kai-Feng Cui(崔凯枫), and Xue-Ren Huang(黄学人)

2022 (8): 83102-083102. doi: 10.1088/1674-1056/ac5880

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The dynamic polarizabilities of ${\rm 3s}^2\,^1{\rm S}_0$ and ${\rm 3s}{\rm 3p}\,^3{\rm P}_0^{\rm o}$ states of Al$^+$ are calculated using the hybrid configuration interaction and many-body perturbation theory method, and multiconfiguration Dirac-Hartree-Fock method in this work. Five ultraviolet magic wavelengths for the Al$^+$ clock transition ${\rm 3s}^2\,^1{\rm S}_0$-${\rm 3s3p}\,^3{\rm P}_0^{\rm o}$ are predicted. Although the suitable lasers are not available presently, the potential precision measurement on these magic wavelengths for the Al$^+$ clock transition would be used to extract the ratios of several certain transition matrix elements with high accuracy, and then help to improve the precision and reliability of the estimate of the BBR shift of the Al$^+$ clock transition. The differential dynamic polarizabilities at certain wavelengths are evaluated, which are useful to assess the ac Stark shift of the Al$^+$ clock transition frequency and helpful in the clock experiments to suppress the ac Stark shift of the clock transition as possible as it can.

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Effect of conical intersection of benzene on non-adiabatic dynamics

Duo-Duo Li(李多多) and Song Zhang(张嵩)

2022 (8): 83103-083103. doi: 10.1088/1674-1056/ac5607

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The effect of conical intersection on the excited dynamics of benzene is studied by ab initio theory of electronic structure, which provides an important insight into photophysical and photochemical reactions. Based on the CASSCF(6,6)/6-31+G(d, p) method, the topological structures of conical intersections S₁/S and S₂/S₁ of benzene, as well as the optimal structures of the ground state (S) and excited states (S₁, S₂), are determined. The energy minima of the S₁ state and S₂ state are estimated at 4.608 eV and 6.889 eV, respectively. In addition, the energy values of the conical intersections of S₁/S and S₂/S₁ are predicted to be 5.600 eV and 6.774 eV. According to the topological structures and energy values of the S₂/S₁ and S₁/S conical intersections, the photophysical behavior of benzene excited to the S₂ state and the effects of the S₂/S₁ and S₁/S conical intersections are discussed in detail.

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Nuclear dissociation after the O 1s $\rightarrow (^4\Sigma_\text{u}^-)$3sσ excitation in O$_2$ molecules

Bocheng Ding(丁伯承), Ruichang Wu(吴睿昌), Yunfei Feng(封云飞), and Xiaojing Liu(刘小井)

2022 (8): 83301-083301. doi: 10.1088/1674-1056/ac560b

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We investigate the dissociation dynamics of core-excited $\mathrm{O}_2$ molecules using a high-resolution energy-resolved electron-ion coincidence experimental setup. The excited cationic states with two valence holes and one Rydberg electron are created after spectator Auger decay induced by $\mathrm{O}$ 1s $\rightarrow (^4\Sigma_{\rm u}^-)3{\rm s}\sigma$ core excitation in $\mathrm{O}_2$. From the energy correlation between the kinetic energy of the Auger electron and the ion kinetic energy release, we distinguish several dissociation channels. Rather complex dissociation channels of the spectator Auger final states are disclosed, which can be explained by the increased number of the crossing point due to the existence of Rydberg electron. The quantum system will evolve into different dissociation limits at each crossing point between the potential energy curves.

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Elastic electron scattering with CH₂Br₂ and CCl₂Br₂: The role of the polarization effects

Xiaoli Zhao(赵小利) and Kedong Wang(王克栋)

2022 (8): 83402-083402. doi: 10.1088/1674-1056/ac4482

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We present elastic electron scattering cross sections with holmethane molecules CH₂Br₂ and CCl₂Br₂ in the low-energy region ranging from 0.01 eV to 20 eV. The calculations are performed with the R-matrix method in static-exchange plus polarization (SEP) and close-coupling (CC) approximations. The integral, differential, and momentum transfer cross sections are calculated. The convergence of the obtained cross sections is checked at four different levels of SEP approximation. The predicted positions of the resonances agree well with available results. The precise resonance parameters are found to be sensitive to the treatment of polarization effects employed. We find that the polarization has a substantial effect on the cross sections, and this effect becomes even more important for lower impact energies.

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Design method of reusable reciprocal invisibility and phantom device

Cheng-Fu Yang(杨成福), Li-Jun Yun(云利军), and Jun-Wei Li(李俊玮)

2022 (8): 84101-084101. doi: 10.1088/1674-1056/ac6166

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Reusable reciprocal invisibility and phantom device is proposed and designed based on multi-folded transformation optics and equivalent components. In comparison with the reported reciprocal invisibility cloaks, the material parameters of the device presented here are homogeneous, and the hiding of the target object does not require any "anti-object" at all, which dramatically breaks through the limitations of the "anti-object" design in previous reciprocal cloak design. Perfectly illusion effect is also found by reasonably setting the material parameters of the restored medium of the device, which can be used to confuse detection radars while hiding target objects. Last but not least, the proposed device has an open structure, which enables the target object enclosed by the device to perform material exchange and simplex transfer of information with the outside world through open channels. In other words, the proposed device has a reusable function, enabling stealth or phantom of new target objects without changing any parameters of the device.

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Imaging a periodic moving/state-changed object with Hadamard-based computational ghost imaging

Hui Guo(郭辉), Le Wang(王乐), and Sheng-Mei Zhao(赵生妹)

2022 (8): 84201-084201. doi: 10.1088/1674-1056/ac6498

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We propose a method for imaging a periodic moving/state-changed object based on computational ghost imaging with Hadamard speckle patterns and a slow bucket detector, named as PO-HCGI. In the scheme, speckle patterns are produced from a part of each row of a Hadamard matrix. Then, in each cycle, multiple speckle patterns are projected onto the periodic moving/state-changed object, and a bucket detector with a slow sampling rate records the total intensities reflected from the object as one measurement. With a series of measurements, the frames of the moving/state-changed object can be obtained directly by the second-order correlation function based on the Hadamard matrix and the corresponding bucket detector measurement results. The experimental and simulation results demonstrate the validity of the PO-HCGI. To the best of our knowledge, PO-HCGI is the first scheme that can image a fast periodic moving/state-changed object by computational ghost imaging with a slow bucket detector.

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Orthogonal-triangular decomposition ghost imaging

Jin-Fen Liu(刘进芬), Le Wang(王乐), and Sheng-Mei Zhao(赵生妹)

2022 (8): 84202-084202. doi: 10.1088/1674-1056/ac5e99

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Ghost imaging (GI) offers great potential with respect to conventional imaging techniques. However, there are still some obstacles for reconstructing images with high quality, especially in the case that the orthogonal measurement matrix is impossible to construct. In this paper, we propose a new scheme based on the orthogonal-triangular (QR) decomposition, named QR decomposition ghost imaging (QRGI) to reconstruct a better image with good quality. In the scheme, we can change the randomly non-orthogonal measurement matrix into orthonormal matrix by performing QR decomposition in two cases. (1) When the random measurement matrix is square, it can be firstly decomposed into an orthogonal matrix $\bm Q$ and an upper triangular matrix $\bm R$. Then let the off-diagonal values of $\bm R$ equal to 0.0, the diagonal elements of $\bm R$ equal to a constant $k$, where $k$ is the average of all values of the main diagonal, so the resulting measurement matrix can be obtained. (2) When the random measurement matrix is with full rank, we firstly compute its transpose, and followed with above QR operation. Finally, the image of the object can be reconstructed by correlating the new measurement matrix and corresponding bucket values. Both experimental and simulation results verify the feasibility of the proposed QRGI scheme. Moreover, the results also show that the proposed QRGI scheme could improve the imaging quality comparing to traditional GI (TGI) and differential GI (DGI). Besides, in comparison with the singular value decomposition ghost imaging (SVDGI), the imaging quality and the reconstruction time by using QRGI are similar to those by using SVDGI, while the computing time (the time consuming on the light patterns computation) is substantially shortened.

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Spatial and spectral filtering of tapered lasers by using tapered distributed Bragg reflector grating

Jing-Jing Yang(杨晶晶), Jie Fan(范杰), Yong-Gang Zou(邹永刚),Hai-Zhu Wang(王海珠), and Xiao-Hui Ma(马晓辉)

2022 (8): 84203-084203. doi: 10.1088/1674-1056/ac5391

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A 1040 nm tapered laser with tapered distributed Bragg reflector (DBR) grating is designed and fabricated. By designing the grating with tapered layout, the tapered DBR grating exhibits the scattering effect on side backward-traveling waves, thus achieving additional suppression of parasitic oscillation. Under the suppression of parasitic oscillation, the spatial and spectral characteristics of the tapered laser are improved. The experimental results show that a near-Gaussian far-field distribution and a kink-free P-I characteristics are achieved, and a single peak emission with a wavelength of 1046.84 nm and a linewidth of 56 pm is obtained.

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Optical fiber FBG linear sensing systems for the on-line monitoring of airborne high temperature air duct leakage

Qinyu Wang(王沁宇), Xinglin Tong(童杏林), Cui Zhang(张翠), Chengwei Deng(邓承伟), Siyu Xu(许思宇), and Jingchuang Wei(魏敬闯)

2022 (8): 84204-084204. doi: 10.1088/1674-1056/ac5889

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Electrical sensing systems, such as those involving eutectic salt, are mostly used in connection to leakage from existing airborne high-temperature air-conducting pipelines. Such complex structured systems are susceptible to external interferences and, thus, cannot meet the increasingly strict monitoring needs of a complex air-conducting pipeline system of an aircraft. In view of this point, this paper studies an alternative sensor system based on a dense array fiber grating. To obtain a compact and light-weight airborne signal processing system, a field programmable gate array is used as the main control core that controls the output of the light source. The functions of pulse modulation, analog-to-digital conversion, data buffering and transmission are integrated into a single system, while the linear sensing monitoring is obtained by detecting the time-division and wavelength-division wavelength drift signals of the fiber Bragg grating array. Our experiments show that the spatial resolution of the linear sensing system approaches 5 cm, the temperature measurement accuracy reaches 2 ℃, the temperature measurement range is between 0-250 ℃, and the response time is within 4 s. Compared with the existing electrical monitoring systems, various monitoring indicators have been greatly improved and have broad application prospects.

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Numerical study of converting beat-note signals of dual-frequency lasers to optical frequency combs by optical injection locking of semiconductor lasers

Chenhao Liu(刘晨浩), Haoshu Jin(靳昊澍), Hui Liu(刘辉), and Jintao Bai(白晋涛)

2022 (8): 84205-084205. doi: 10.1088/1674-1056/ac649a

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The optical injection locking of semiconductor lasers to dual-frequency lasers is studied by numerical simulations. The beat-note signals can be effectively transformed to optical frequency combs due to the effective four wave-mixing in the active semiconductor gain medium. The low-noise Gaussian-like pulse can be obtained by locking the relaxation oscillation and compensating the gain asymmetry. The simulations suggest that pulse trains of width below 30 ps and repetition rate in GHz frequency can be generated simply by the optical injection locking of semiconductor lasers. Since the optical injection locking can broaden the spectrum and amplify the optical power simultaneously, it can be a good initial stage for generating optical frequency combs from dual-frequency lasers by multi-stage of spectral broadening in nonlinear waveguides.

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A 45-μJ, 10-kHz, burst-mode picosecond optical parametric oscillator synchronously pumped at a second harmonic cavity

Chao Ma(马超), Ke Liu(刘可), Yong Bo(薄勇), Zhi-Min Wang(王志敏), Da-Fu Cui(崔大复), and Qin-Jun Peng(彭钦军)

2022 (8): 84206-084206. doi: 10.1088/1674-1056/ac6016

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A novel high-energy picosecond optical parametric oscillator (OPO) was realized by placing an OPO in a second-harmonic (SH) cavity. In a proof-of-principle experiment, we demonstrated excellent burst energy of 45 μJ for the OPO signal at 900 nm that operates at a pulse repetition rate of 10 kHz and a pulse width of 46.8 ps. The beam quality was measured as $M^{2}_{x} = 1.44$ and $M^{2}_{y} = 1.40$ in the orthogonal directions, corresponding to an average beam factor $M^{2} = 1.42$. So far, this study is the first to investigate high-energy ps OPO synchronously pumped in a second-harmonic cavity.

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High sensitivity dual core photonic crystal fiber sensor for simultaneous detection of two samples

Pibin Bing(邴丕彬), Guifang Wu(武桂芳), Qing Liu(刘庆), Zhongyang Li(李忠洋),Lian Tan(谭联), Hongtao Zhang(张红涛), and Jianquan Yao(姚建铨)

2022 (8): 84208-084208. doi: 10.1088/1674-1056/ac4a68

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The optical control ability of photonic crystal fiber (PCF) is a distinctive property suitable for improving sensing and plasma performance. This article proposes a dual-core D-channel PCF sensor that can detect two samples simultaneously, which effectively solves the problems of coating difficulty and low wavelength sensitivity. The PCF has four layers of air holes, which dramatically reduces the optical fiber loss and is more conducive to the application of sensors in actual production. In addition, by introducing dual cores on the upper and lower sides of the central air hole, reducing the spacing between the core and the gold nanolayer, a stronger evanescent field can be generated in the cladding air hole. The optical fiber sensor can detect the refractive index of two samples simultaneously with a maximum sensitivity of 21300 nm/RIU. To the best of our knowledge, the sensitivity achieved in this work is the highest sensitivity with the dual sample synchronous detection sensors. The detection range of the refraction index is 1.35-1.41, and the resolution of the sensor is 4.695×10^-6. Overall, the sensor will be suitable for medical detection, organic chemical sensing, analyte detection, and other fields.

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High power supercontinuum generation by dual-color femtosecond laser pulses in fused silica

Saba Zafar, Dong-Wei Li(李东伟), Acner Camino, Jun-Wei Chang(常峻巍), and Zuo-Qiang Hao(郝作强)

2022 (8): 84209-084209. doi: 10.1088/1674-1056/ac46be

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High power supercontinuum (SC) is generated by focusing 800 nm and 400 nm femtosecond laser pulses in fused silica with a microlens array. It is found that the spectrum of the SC is getting broader compared with the case of a single laser pulse, and the spectral energy density between the two fundamental laser wavelengths is getting significantly higher by optimizing the phase matching angle of the BBO. It exceeds μJ/nm over 490 nm range which is from 380 nm to 870 nm, overcoming the disadvantage of relative lower power in the ranges far from the fundamental wavelength.

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Dynamically tunable multiband plasmon-induced transparency effect based on graphene nanoribbon waveguide coupled with rectangle cavities system

Zi-Hao Zhu(朱子豪), Bo-Yun Wang(王波云), Xiang Yan(闫香), Yang Liu(刘洋), Qing-Dong Zeng(曾庆栋), Tao Wang(王涛), and Hua-Qing Yu(余华清)

2022 (8): 84210-084210. doi: 10.1088/1674-1056/ac7e39

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A dynamically tunable multiband plasmon-induced transparency (PIT) effect in a series of rectangle cavities coupled with a graphene nanoribbon waveguide system is investigated theoretically and numerically by tuning the Fermi level of the graphene rectangle cavity. A single-PIT effect is realized using two different methods: one is the direct destructive interference between bright and dark modes, and the other is the indirect coupling through a graphene nanoribbon waveguide. Moreover, dual-PIT effect is obtained by three rectangle cavities side-coupled with a graphene nanoribbon waveguide. Results show that the magnitude of the dual-PIT window can be controlled between 0.21 and 0.74, and the corresponding group index is controlled between 143.2 and 108.6. Furthermore, the triple-PIT effect is achieved by the combination of bright-dark mode coupling and the cavities side-coupled with waveguide mechanism. Thus, sharp PIT windows can be formed, a high transmission is maintained between 0.51 and 0.74, and the corresponding group index is controlled between 161.4 and 115.8. Compared with previously proposed graphene-based PIT effects, the size of the introduced structure is less than 0.5 μm². Particularly, the slow light effect is crucial in the current research. Therefore, a novel approach is introduced toward the realization of optical sensors, optical filters, and slow light and light storage devices with ultra-compact, multiband, and dynamic tunable.

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Three-dimensional coupled-mode model and characteristics of low-frequency sound propagation in ocean waveguide with seamount topography

Ya-Xiao Mo(莫亚枭), Chao-Jin Zhang(张朝金), Li-Cheng Lu(鹿力成), and Sheng-Ming Guo(郭圣明)

2022 (8): 84301-084301. doi: 10.1088/1674-1056/ac538f

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Large-scale topography, such as a seamount, substantially impacts low-frequency sound propagation in an ocean waveguide, limiting the application of low-frequency acoustic detecting techniques. A three-dimensional (3D) coupled-mode model is developed to calculate the acoustic field in an ocean waveguide with seamount topography and analyze the 3D effect. In this model, a correction is introduced in the bottom boundary, theoretically making the acoustic field satisfy the energy conservation. Furthermore, a large azimuth angle calculation range is obtained by using the operator theory and higher-order Padé approximation. Additionally, the model has advantages related to the coupling mode and parabolic equation theory. The couplings corresponding to the effects of range-dependent environment are fully considered, and the numerical implementation is kept feasible. After verifying the accuracy and reliability of the model, low-frequency sound propagation characteristics in the seamount environment are analyzed. The results indicate lateral variability in bathymetry can lead to out-of-plane effects such as the horizontal refraction phenomenon, while the coupling effect tends to restore the abnormal sound field and produces acoustic field diffraction behind the seamount. This model effectively considers the effects of the horizontal refraction and coupling, which are proportional to the scale of the seamount.

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Sound-transparent anisotropic media for backscattering-immune wave manipulation

Wei-Wei Kan(阚威威), Qiu-Yu Li(李秋雨), and Lei Pan(潘蕾)

2022 (8): 84302-084302. doi: 10.1088/1674-1056/ac4904

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The scattering behavior of an anisotropic acoustic medium is analyzed to reveal the possibility of routing acoustic signals through the anisotropic layers with no backscattering loss. The sound-transparent effect of such a medium is achieved by independently modulating the anisotropic effective acoustic parameters in a specific order, and is experimentally observed in a bending waveguide by arranging the subwavelength structures in the bending part according to transformation acoustics. With the properly designed filling structures, the original distorted acoustic field in the bending waveguide is restored as if the wave travels along a straight path. The transmitted acoustic signal is maintained nearly the same as the incident modulated Gaussian pulse. The proposed schemes and the supporting results could be instructive for further acoustic manipulations such as wave steering, cloaking and beam splitting.

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Effect of pressure evolution on the formation enhancement in dual interacting vortex rings

Jianing Dong(董佳宁), Yang Xiang(向阳), Hong Liu(刘洪), and Suyang Qin(秦苏洋)

2022 (8): 84701-084701. doi: 10.1088/1674-1056/ac65f6

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In the biological locomotion, the ambit pressure is of particular importance to use as a means of propulsion. The multiple vortex rings have been proved to generate additional thrust by interaction, but the mechanism of this thrust enhancement is still unknown. This study examines the effect of ambit pressure on formation enhancement in interacting dual vortex rings. The vortex rings, which have the same formation time, are successively generated in a piston-cylinder apparatus. The finite-time Lyapunov exponent (FTLE) visualizes the flow fields as an indication of Lagrangian coherent structures (LCSs), and the pressure field is calculated based on the digital particle image velocity (DPIV). We extract the back pressure of the rear vortex in dual vortices and the back pressure circulation $\varGamma_{\rm b}$, which is defined as a form of overpressure circulation $\varGamma_{\rm p}$. The $\varGamma_{\rm b}$ has a positive linear relationship with $\varGamma_{\rm p}$. A critical interval distance $d_{\rm cr}^*$ in a range of 0.32-0.42 is found where $\varGamma_{\rm b}$ and $\varGamma_{\rm p}$ reach the maximum synchronously, leading to a full-interaction mode. Moreover, an over-interaction mode and an under-interaction mode are proposed when the dimensionless interval distance $d^*$ is smaller or larger than $d_{\rm cr}^*$. To conclude, the high back pressure caused by vortex interaction can enhance the formation of vortex rings and lead to high thrust.

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Drop impact on substrates with heterogeneous stiffness

Yang Cheng(成阳), Jian-Gen Zheng(郑建艮), Chen Yang(杨晨), Song-Lei Yuan(袁松雷), Guo Chen(陈果), and Li-Yu Liu(刘雳宇)

2022 (8): 84702-084702. doi: 10.1088/1674-1056/ac5c33

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Previous studies of drop impact mainly focus on homogeneous substrates while heterogeneous substrates remain largely unexplored. A convenient preparation strategy of stiff heterogeneous substrates is presented in this work, and the drop impact on such a stiffness-patterned substrate consisting of soft spirals surrounded by a rigid region is systematically investigated. The results show that the splash behavior of a drop on a stiffness-patterned substrate exhibits distinct characteristics from those on a homogeneous substrate. Prompt splash is more likely to occur on the substrate with the greater heterogeneity of stiffness, which is reflected in the lower critical impact velocity. Moreover, the splash velocity of emitted droplet is significantly larger on the heterogeneous substrate than that on a corresponding homogeneous substrate, especially at a higher impact velocity of the drop, indicating a stronger splash intensity on the heterogeneous substrate. The difference in drop splashing between homogeneous substrate and heterogeneous substrate is largely due to the stiffness heterogeneity, rather than the variation of overall stiffness of the substrate. The use of spiral shape provides a feasible solution for introducing stiffness heterogeneity of substrate. This study is conducive to the understanding of drop impact research beyond uniform substrates, reveals the potential of using stiffness-patterned substrates to control splash, and may find useful applications in industries related to drop impact and splash.

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Physical aspects of magnetized Jeffrey nanomaterial flow with irreversibility analysis

Fazal Haq, Muhammad Ijaz Khan, Sami Ullah Khan, Khadijah M Abualnaja, and M A El-Shorbagy

2022 (8): 84703-084703. doi: 10.1088/1674-1056/ac4236

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This research presents the applications of entropy generation phenomenon in incompressible flow of Jeffrey nanofluid in the presence of distinct thermal features. The novel aspects of various features, such as Joule heating, porous medium, dissipation features, and radiative mechanism are addressed. In order to improve thermal transportation systems based on nanomaterials, convective boundary conditions are introduced. The thermal viscoelastic nanofluid model is expressed in terms of differential equations. The problem is presented via nonlinear differential equations for which analytical expressions are obtained by using the homotopy analysis method (HAM). The accuracy of solution is ensured. The effective outcomes of all physical parameters associated with the flow model are carefully examined and underlined through various curves. The observations summarized from current analysis reveal that the presence of a permeability parameter offers resistance to the flow. A monotonic decrement in local Nusselt number is noted with Hartmann number and Prandtl number. Moreover, entropy generation and Bejan number increases with radiation parameter and fluid parameter.

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Combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy

Qing-Xue Li(李庆雪), Dan Zhang(张丹), Yuan-Fei Jiang(姜远飞), Su-Yu Li(李苏宇), An-Min Chen(陈安民), and Ming-Xing Jin(金明星)

2022 (8): 85201-085201. doi: 10.1088/1674-1056/ac597a

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A combination of spark discharge and nanoparticle-enhanced laser-induced plasma spectroscopy is investigated. Depositing Au nanoparticles at the surface of a brass target can enhance the coupling of the target and the laser. More atoms in the brass sample are excited. As a secondary excitation source, spark discharge reheats the generated plasma, which further amplifies the enhancement results of nanoparticles. The spectral intensity with the spark discharge increases more obviously with nanoparticle concentration increasing than without the spark discharge. Also, plasma temperature and electron density are calculated by the Boltzmann plot and Stark broadening. The changes in the plasma temperature and electron density are consistent with the spectral emission changes.

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Substitutions of vertex configuration of Ammann-Beenker tiling in framework of Ammann lines

Jia-Rong Ye(叶家容), Wei-Shen Huang(黄伟深), and Xiu-Jun Fu(傅秀军)

2022 (8): 86101-086101. doi: 10.1088/1674-1056/ac5981

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The Ammann-Beenker tiling is a typical model for two-dimensional octagonal quasicrystals. The geometric properties of local configurations are the key to understanding its formation mechanism. We study the configuration correlations in the framework of Ammann lines, giving an in-depth inspection of this eightfold symmetric structure. When both the vertex type and the orientation are taken into account, strict confinements of neighboring vertices are found. These correlations reveal the structural properties of the quasilattice and also provide substitution rules of vertex along an Ammann line.

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Radiation effects of electrons on multilayer FePS₃ studied with laser plasma accelerator

Meng Peng(彭猛), Jun-Bo Yang(杨俊波), Hao Chen(陈浩), Bo-Yuan Li(李博源), Xu-Lei Ge(葛绪雷), Xiao-Hu Yang(杨晓虎), Guo-Bo Zhang(张国博), and Yan-Yun Ma(马燕云)

2022 (8): 86102-086102. doi: 10.1088/1674-1056/ac5c34

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Space radiation with inherently broadband spectral flux poses a huge danger to astronauts and electronics on aircraft, but it is hard to simulate such feature with conventional radiation sources. Using a tabletop laser-plasma accelerator, we can reproduce exponential energy particle beams as similar as possible to these in space radiation. We used such an electron beam to study the electron radiation effects on the surface structure and performance of two-dimensional material (FePS₃). Energetic electron beam led to bulk sample cleavage and damage between areas of uneven thickness. For the FePS₃ sheet sample, electron radiation transformed it from crystalline state to amorphous state, causing the sample surface to rough. The full widths at the half maximum of characteristic Raman peaks became larger, and the intensities of characteristic Raman peaks became weak or even disappeared dramatically under electron radiation. This trend became more obvious for thinner samples, and this phenomenon was attributed to the cleavage of P-P and P-S bonds, destabilizing the bipyramid structure of [P₂S₆]^4- unit. The results are of great significance for testing the maximum allowable radiation dose for the two-dimensional material, implying that FePS₃ cannot withstand such energetic electron radiation without an essential shield.

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Synthesis of hexagonal boron nitride films by dual temperature zone low-pressure chemical vapor deposition

Zhi-Fu Zhu(朱志甫), Shao-Tang Wang(王少堂), Ji-Jun Zou(邹继军), He Huang(黄河), Zhi-Jia Sun(孙志嘉), Qing-Lei Xiu(修青磊), Zhong-Ming Zhang(张忠铭), Xiu-Ping Yue(岳秀萍), Yang Zhang(张洋), Jin-Hui Qu(瞿金辉), and Yong Gan(甘勇)

2022 (8): 86103-086103. doi: 10.1088/1674-1056/ac657d

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Hexagonal boron nitride (h-BN) films are synthesized by dual temperature zone low-pressure chemical vapor deposition (LPCVD) through using a single ammonia borane precursor on non-catalytic c-plane Al₂O₃ substrates. The grown films are confirmed to be h-BN films by various characterization methods. Meanwhile, the growth rates and crystal quality of h-BN films at different positions in the dual temperature zone are studied. It is found that the growth rates and crystal quality of the h-BN films at different positions on the substrate are significantly different. The growth rates of the h-BN thin films show their decreasing trends with the rearward position, while the crystal quality is improved. This work provides an experimental basis for the preparation of large area wafer thick h-BN films by LPCVD.

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Core structure and Peierls stress of the 90° dislocation and the 60° dislocation in aluminum investigated by the fully discrete Peierls model

Hao Xiang(向浩), Rui Wang(王锐), Feng-Lin Deng(邓凤麟), and Shao-Feng Wang(王少峰)

2022 (8): 86104-086104. doi: 10.1088/1674-1056/ac587f

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The core structure, Peierls stress and core energy, etc. are comprehensively investigated for the $90^\circ$ dislocation and the $60^\circ$ dislocation in metal aluminum using the fully discrete Peierls model, and in particular thermal effects are included for temperature range $0\leq T \leq 900$ K. For the $90^\circ$ dislocation, the core clearly dissociates into two partial dislocations with the separating distance $D\sim 12$ Å, and the Peierls stress is very small $\sigma_{\rm p}<1$ kPa. The nearly vanishing Peierls stress results from the large characteristic width and a small step length of the $90^\circ$ dislocation. The $60^\circ$ dislocation dissociates into $30^\circ$ and $90^\circ$ partial dislocations with the separating distance $D\sim 11$ Å. The Peierls stress of the $60^\circ$ dislocation grows up from $1$ MPa to $2$ MPa as the temperature increases from $0$ K to $900$ K. Temperature influence on the core structures is weak for both the $90^\circ$ dislocation and the $60^\circ$ dislocation. The core structures theoretically predicted at $T=0$ K are also confirmed by the first principle simulations.

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Theoretical and experimental studies on high-power laser-induced thermal blooming effect in chamber with different gases

Xiangyizheng Wu(吴祥议政), Jian Xu(徐健), Keling Gong(龚柯菱), Chongfeng Shao(邵崇峰), Yang Kou(寇洋), Yuxuan Zhang(张宇轩), Yong Bo(薄勇), and Qinjun Peng(彭钦军)

2022 (8): 86105-086105. doi: 10.1088/1674-1056/ac6165

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High-power laser induced thermal blooming effects in a closed chamber with three different gases are investigated theoretically and experimentally in this work. In the theoretical treatment, an incompressible gas turbulent model is adopted. In the numerical simulation the gas refractive index as a function of both the temperature and pressure is taken into consideration. In the experimental study the pump-probe technology is adopted. A high-power 1064-nm fiber laser with maximum output power of 12 kW is used to drive the gas thermal blooming, and a 50-mW high-beam-quality 637-nm laser diode (LD) is used as a probe beam. The influences of the gas thermal blooming in the chamber on the probe beam wavefront and beam quality are analyzed for three different gases of air, nitrogen, and helium, respectively. The results indicate that nitrogen is well suitable for restraining thermal blooming effect for high-power laser. The measured data are in good agreement with the simulated results.

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Angular dependence of proton-induced single event transient in silicon-germanium heterojunction bipolar transistors

Jianan Wei(魏佳男), Yang Li(李洋), Wenlong Liao(廖文龙), Fang Liu(刘方), Yonghong Li(李永宏), Jiancheng Liu(刘建成), Chaohui He(贺朝会), and Gang Guo(郭刚)

2022 (8): 86106-086106. doi: 10.1088/1674-1056/ac5d32

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We investigate the angular dependence of proton-induced single event transient (SET) in silicon-germanium heterojunction bipolar transistors. Experimental results show that the overall SET cross section is almost independent of proton incident angle. However, the proportion of SET events with long duration and high integral charge collection grows significantly with the increasing angle. Monte Carlo simulations demonstrate that the integral cross section of proton incident events with high ionizing energy deposition in the sensitive volume tends to be higher at larger incident angles, which is associated with the angular distribution of proton-induced secondary particles and the geometry of sensitive volume.

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First-principles study of a new BP₂ two-dimensional material

Zhizheng Gu(顾志政), Shuang Yu(于爽), Zhirong Xu(徐知荣), Qi Wang(王琪), Tianxiang Duan(段天祥), Xinxin Wang(王鑫鑫), Shijie Liu(刘世杰), Hui Wang(王辉), and Hui Du(杜慧)

2022 (8): 86107-086107. doi: 10.1088/1674-1056/ac5a40

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Two-dimensional materials have a wide range of applications in many aspects due to their unique properties. Here we carry out a detailed structural search and design of the BP₂ using the first principles method, and find a new PMM2 sheet. The analysis of the phonon dispersive curves shows that the 2D PMM2 is dynamic stable. The study of molecular dynamics shows that the 2D PMM2 can be stable under high temperature, even at 600 K. Most importantly, when a suitable strain is applied, the structure can exhibit other electronic properties such as direct band gap semiconductor. In addition, the small strain can tune the band gap value of the PMM2 structure to around 1.4 eV, which is very close to the ideal band gap of solar materials. Therefore, the 2D PMM2 may have potential applications in the field of photovoltaic materials.

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Spatial correlation of irreversible displacement in oscillatory-sheared metallic glasses

Shiheng Cui(崔世恒), Huashan Liu(刘华山), and Hailong Peng(彭海龙)

2022 (8): 86108-086108. doi: 10.1088/1674-1056/ac65f3

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We report computer simulations on the oscillatory of CuZr metallic glasses at zero temperature with different shear amplitudes. In small system a homogenous shear deformation is found, while in large system an inhomogeneous shear deformation is found with a shear band formed. Concomitantly, spatial correlation of irreversible displacement exhibits an isotropic and exponential decay in the case of homogeneous deformation, whereas a mixed power-law and exponential decay in the case of anisotropic and inhomogeneous deformation. By projecting the azimuthal-dependent correlation function onto the spherical harmonics, we found a strong polar symmetry that accounts for the emerged shear band, and a weaker quadrupolar symmetry that accounts for the elastic filed generated by Eshelby inclusions. By this, we conclude that the anisotropy and decaying formula of the plastic correlation are dominated by the homogeneity or inhomogeneity for the deformation in the metallic glasses.

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Ru thickness-dependent interlayer coupling and ultrahigh FMR frequency in FeCoB/Ru/FeCoB sandwich trilayers

Le Wang(王乐), Zhao-Xuan Jing(荆照轩), Ao-Ran Zhou(周傲然), and Shan-Dong Li(李山东)

2022 (8): 86201-086201. doi: 10.1088/1674-1056/ac693f

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The antiferromagnetic (AFM) interlayer coupling effective field in a ferromagnetic/non-magnetic/ferromagnetic (FM/NM/FM) sandwich structure, as a driving force, can dramatically enhance the ferromagnetic resonance (FMR) frequency. Changing the non-magnetic spacer thickness is an effective way to control the interlayer coupling type and intensity, as well as the FMR frequency. In this study, FeCoB/Ru/FeCoB sandwich trilayers with Ru thickness ($t_{\rm Ru}$) ranging from 1 Å to 16 Å are prepared by a compositional gradient sputtering (CGS) method. It is revealed that a stress-induced anisotropy is present in the FeCoB films due to the B composition gradient in the samples. A $t_{\mathrm{Ru}}$-dependent oscillation of interlayer coupling from FM to AFM with two periods is observed. An AFM coupling occurs in a range of $2 {\rm Å} \le t_{\rm Ru} \le 8 {\rm Å}$ and over 16 $\mathrm{Å}$, while an FM coupling is present in a range of $t_{\rm Ru}< 2$ Å and $9 {\rm Å} \le t_{\rm Ru} \le 14.5 Å$. It is interesting that an ultrahigh optical mode (OM) FMR frequency in excess of 20 GHz is obtained in the sample with ${t}_{\mathrm{Ru}}= 2.5 \mathrm{Å}$ under an AFM coupling. The dynamic coupling mechanism in trilayers is simulated, and the corresponding coupling types at different values of $t_{\mathrm{Ru}}$ are verified by Layadi's rigid model. This study provides a controllable way to prepare and investigate the ultrahigh FMR films.

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Nonvanishing optimal noise in cellular automaton model of self-propelled particles

Guang-Le Du(杜光乐) and Fang-Fu Ye(叶方富)

2022 (8): 86401-086401. doi: 10.1088/1674-1056/ac67c4

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A minimal cellular automaton model is introduced to describe the collective motion of self-propelled particles on two-dimensional square lattice. The model features discretization of directional and positional spaces and single-particle occupation on one lattice site. Contrary to the Vicsek model and its variants, our model exhibits the nonvanishing optimal noise. When the particle density increases, the collective motion is promoted with optimal noise strength and reduced with noise strength out of optimal region. In addition, when the square lattice undergoes edge percolation process, no abrupt change of alignment behaviors is observed at the critical point of percolation.

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Effects of oxygen concentration and irradiation defects on the oxidation corrosion of body-centered-cubic iron surfaces: A first-principles study

Zhiqiang Ye(叶志强), Yawei Lei(雷亚威), Jingdan Zhang(张静丹), Yange Zhang(张艳革), Xiangyan Li(李祥艳), Yichun Xu(许依春), Xuebang Wu(吴学邦), C. S. Liu(刘长松), Ting Hao(郝汀), and Zhiguang Wang(王志光)

2022 (8): 86802-086802. doi: 10.1088/1674-1056/ac633c

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Oxidation corrosion of steels usually occurs in contact with the oxygen-contained environment, which is accelerated by high oxygen concentration and irradiation. The oxidation mechanism of steels is investigated by the adsorption/solution of oxygen atoms on/under body-centered-cubic (bcc) iron surfaces, and diffusion of oxygen atoms on the surface and in the near-surface region. Energetic results indicate that oxygen atoms prefer to adsorb at hollow and long-bridge positions on the Fe(100) and (110) surfaces, respectively. As the coverage of oxygen atoms increases, oxygen atoms would repel each other and gradually dissolve in the near-surface and bulk region. As vacancies exist, oxygen atoms are attracted by vacancies, especially in the near-surface and bulk region. Dynamic results indicate that the diffusion of O atoms on surfaces is easier than that into near-surface, which is affected by oxygen coverage and vacancies. Moreover, the effects of oxygen concentration and irradiation on oxygen density in the near-surface and bulk region are estimated by the McLean's model with a simple hypothesis.

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Modulation of Schottky barrier in XSi₂N₄/graphene (X=Mo and W) heterojunctions by biaxial strain

Qian Liang(梁前), Xiang-Yan Luo(罗祥燕), Yi-Xin Wang(王熠欣), Yong-Chao Liang(梁永超), and Quan Xie(谢泉)

2022 (8): 87101-087101. doi: 10.1088/1674-1056/ac5c3b

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Reducing the Schottky barrier height (SBH) and even achieving the transition from Schottky contacts to Ohmic contacts are key challenges of achieving high energy efficiency and high-performance power devices. In this paper, the modulation effects of biaxial strain on the electronic properties and Schottky barrier of MoSi₂N₄ (MSN)/graphene and WSi₂N₄ (WSN)/graphene heterojunctions are examined by using first principles calculations. After the construction of heterojunctions, the electronic structures of MSN, WSN, and graphene are well preserved. Herein, we show that by applying suitable external strain to a heterojunction stacked by MSN or WSN — an emerging two-dimensional (2D) semiconductor family with excellent mechanical properties — and graphene, the heterojunction can be transformed from Schottky p-type contacts into n-type contacts, even highly efficient Ohmic contacts, making it of critical importance to unleash the tremendous potentials of graphene-based van der Waals (vdW) heterojunctions. Not only are these findings invaluable for designing high-performance graphene-based electronic devices, but also they provide an effective route to realizing dynamic switching either between n-type and p-type Schottky contacts, or between Schottky contacts and Ohmic contacts.

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Tailored martensitic transformation and enhanced magnetocaloric effect in all-d-metal Ni₃₅Co₁₅Mn₃₃Fe₂Ti₁₅ alloy ribbons

Yong Li(李勇), Liang Qin(覃亮), Hongguo Zhang(张红国), and Lingwei Li(李领伟)

2022 (8): 87103-087103. doi: 10.1088/1674-1056/ac6edf

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The crystal structure, martensitic transformation and magnetocaloric effect have been studied in all-$d$-metal Ni$_{35}$Co$_{15}$Mn$_{33}$Fe$_{2}$Ti$_{15}$ alloy ribbons with different wheel speeds (15 m/s (S15), 30 m/s (S30), and 45 m/s (S45)). All three ribbons crystalize in B2-ordered structure at room temperature with crystal constants of 5.893(2) Å, 5.898(4) Å, and 5.898(6) Å, respectively. With the increase of wheel speed, the martensitic transformation temperature decreases from 230 K to 210 K, the Curie temperature increases slightly from 371 K to 378 K. At the same time, magnetic entropy change ($\Delta S_{\rm m}$) is also enhanced, as well as refrigeration capacity ($RC$). The maximum $\Delta S_{\rm m}$ of 15.6(39.7) J/kg$\cdot$K and $RC$ of 85.5 (212.7) J/kg under $\Delta H = 20$ (50) kOe (1 ${\rm Oe}=79.5775$ A$\cdot$m$^{-1}$) appear in S45. The results indicate that the ribbons could be the candidate for solid-state magnetic refrigeration materials.

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Analytical formula describing the non-saturating linear magnetoresistance in inhomogeneous conductors

Shan-Shan Chen(陈珊珊), Yang Yang(杨阳), and Fan Yang(杨帆)

2022 (8): 87303-087303. doi: 10.1088/1674-1056/ac6582

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The effective-medium theory (EMT) has proved successful in modeling the non-saturating linear magnetoresistance induced by inhomogeneity. However, calculating magnetoresistance using the EMT usually involves solving coupled integral equations which have no analytical solutions, and therefore, it is still difficult to directly compare the predictions of EMT with experimental data. Here we demonstrate that the linear magnetoresistance predicted by the EMT can be either exactly formulated or well approximated by a simple analytical equation $\Delta\rho/\rho_0=\sqrt{k^2B^2+a^2}-a$ in a number of known situations. The relations between the EMT parameters and the phenomenological parameters $k$ and $a$ are evaluated. Our results provide a convenient and effective method for extracting the EMT parameters from experimental data.

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Magnetic properties of a mixed spin-3/2 and spin-2 Ising octahedral chain

Xiao-Chen Na(那小晨), Nan Si(司楠), Feng-Ge Zhang(张凤阁), and Wei Jiang(姜伟)

2022 (8): 87502-087502. doi: 10.1088/1674-1056/ac5885

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Using an effective field theory with correlations, magnetic properties of an octahedral chain described by a mixed spin Ising model are investigated. Unique phenomena such as multiple hysteresis loops, saturation magnetization, and reverse flip of the magnetization plateaus occur when certain typical parameters are applied. These results may be helpful to further investigate the magnetic properties of one-dimensional systems and could potentially be utilized in the design of spin devices.

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Exchange-coupling-induced fourfold magnetic anisotropy in CoFeB/FeRh bilayer grown on SrTiO₃(001)

Qingrong Shao(邵倾蓉), Jing Meng(孟婧), Xiaoyan Zhu(朱晓艳), Yali Xie(谢亚丽), Wenjuan Cheng(程文娟), Dongmei Jiang(蒋冬梅), Yang Xu(徐杨), Tian Shang(商恬), and Qingfeng Zhan(詹清峰)

2022 (8): 87503-087503. doi: 10.1088/1674-1056/ac673c

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Exchange coupling across the interface between a ferromagnetic (FM) layer and an antiferromagnetic (AFM) or another FM layer may induce a unidirectional magnetic anisotropy and/or a uniaxial magnetic anisotropy, which has been extensively studied due to the important application in magnetic materials and devices. In this work, we observed a fourfold magnetic anisotropy in amorphous CoFeB layer when exchange coupling to an adjacent FeRh layer which is epitaxially grown on an SrTiO₃(001) substrate. As the temperature rises from 300 K to 400 K, FeRh film undergoes a phase transition from AFM to FM phase, the induced fourfold magnetic anisotropy in the CoFeB layer switches the orientation from the FeRh$\langle 110\rangle $ to FeRh$\langle 100\rangle $ directions and the strength is obviously reduced. In addition, the effective magnetic damping as well as the two-magnon scattering of the CoFeB/FeRh bilayer also remarkably increase with the occurrence of magnetic phase transition of FeRh. No exchange bias is observed in the bilayer even when FeRh is in the nominal AFM state, which is probably because the residual FM FeRh moments located at the interface can well separate the exchange coupling between the below pinned FeRh moments and the CoFeB moments.

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Electromagnetic wave absorption properties of Ba(CoTi)_xFe_12-2xO₁₉@BiFeO₃ in hundreds of megahertz band

Zhi-Biao Xu(徐志彪), Zhao-Hui Qi(齐照辉), Guo-Wu Wang(王国武), Chang Liu(刘畅), Jing-Hao Cui(崔晶浩), Wen-Liang Li(李文梁), and Tao Wang(王涛)

2022 (8): 87504-087504. doi: 10.1088/1674-1056/ac5240

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The high-performance electromagnetic (EM) wave absorption material Ba(CoTi)$_{x}$Fe$_{12-2x}$O$_{19}$@BiFeO$_{3}$ was prepared by solid-state reaction, and its EM wave absorption properties were deeply studied. The results revealed that Ba(CoTi)$_{x}$Fe$_{12-2x}$O$_{19}$@BiFeO$_{3}$ could obtain excellent absorption properties in hundreds of megahertz by adjusting the Co$^{2+}$-Ti$^{4+}$ content. The best comprehensive property was obtained for $x=1.2$, where the optimal reflection loss ($RL$) value reaches $-30.42$ dB at about 600 MHz with thickness of 3.5 mm, and the corresponding effective absorption band covers the frequency range of 437 MHz-1 GHz. Moreover, the EM wave absorption mechanism was studied based on the simulation methods. The simulated results showed that the excellent EM wave absorption properties of Ba(CoTi)$_{x}$Fe$_{12-2x}$O$_{19}$@BiFeO$_{3}$ mainly originated from the internal loss caused by natural resonance, and the interface cancelation further improved the absorption properties and resulted in $RL$ peaks.

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Low-temperature heat transport of the zigzag spin-chain compound SrEr₂O₄

Liguo Chu(褚利国), Shuangkui Guang(光双魁), Haidong Zhou(周海东), Hong Zhu(朱弘), and Xuefeng Sun(孙学峰)

2022 (8): 87505-087505. doi: 10.1088/1674-1056/ac5e97

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Low-temperature thermal conductivity ($\kappa$), as well as the magnetic properties and specific heat, are studied for the frustrated zigzag spin-chain material SrEr$_{2}$O$_{4}$ by using single-crystal samples. The specific heat data indicate the long-range antiferromagnetic transition at $\sim 0.73 $ K and the existence of strong magnetic fluctuations. The magnetizations at very low temperatures for magnetic field along the $c$ axis (spin chain direction) or the $a$ axis reveal the field-induced magnetic transitions. The $\kappa $ shows a strong dependence on magnetic field, applied along the $c$ axis or the $a$ axis, which is closely related to the magnetic transitions. Furthermore, high magnetic field induces a strong increase of $\kappa $. These results indicate that thermal conductivity along either the $c$ axis or the $a$ axis are mainly contributed by phonons, while magnetic excitations play a role of scattering phonons.

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High-dispersive mirror for pulse stretcher in femtosecond fiber laser amplification system

Wenjia Yuan(袁文佳), Weidong Shen(沈伟东), Chen Xie(谢辰), Chenying Yang(杨陈楹), and Yueguang Zhang(章岳光)

2022 (8): 87801-087801. doi: 10.1088/1674-1056/ac5e9a

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We present a high-dispersive multilayer mirror for pulse stretching in a femtosecond fiber laser amplification system. The designed mirror contains 54 layers with a total physical thickness of 7.3 μm, which can provide a positive group delay dispersion (GDD) of 600 fs² and a high reflectance over 99.9% from 1010 to 1070 nm. The samples were prepared by dual ion beam sputtering. The measured transmittance matches well with the theoretical result. The GDD characteristics of samples were tested by home-made white light interferometer. The measured GDD is higher than the design results, an average GDD of +722 fs² from 1010 nm to 1070 nm. The mirrors were employed in a Yb-doped large-mode-area photonic crystal fiber amplification system. An input pulse compressed by the gratings with autocorrelation function of 83 fs is obtained with a stretched FWHM of 1.29 ps after 28 bounces between the dispersive mirrors. The results show that the multilayer dispersive mirror could be an effective and promising technique for pulse stretching in femtosecond amplification systems.

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Improving efficiency of inverted perovskite solar cells via ethanolamine-doped PEDOT:PSS as hole transport layer

Zi-Jun Wang(王子君), Jia-Wen Li(李嘉文), Da-Yong Zhang(张大勇), Gen-Jie Yang(杨根杰), and Jun-Sheng Yu(于军胜)

2022 (8): 87802-087802. doi: 10.1088/1674-1056/ac5988

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In order to fabricate high-performance inverted perovskite solar cells (PeSCs), an appropriate hole transport layer (HTL) is essential since it will affect the hole extraction at perovskite/HTL interface and determine the crystallization quality of the subsequent perovskite films. Herein, a facile and simple method is developed by adding ethanolamine (ETA) into poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as HTL. The doping of a low-concentration ETA can efficiently modify the electrical properties of the PEDOT:PSS film and lower the highest occupied molecular orbital (HOMO) level, which is more suitable for the hole extraction from the perovskite to HTL. Besides, ETA-doped PEDOT:PSS will create a perovskite film with larger grain size and higher crystallinity. Hence, the results show that the open-circuit voltage of the device increases from 0.99 V to 1.06 V, and the corresponding power conversion efficiency (PCE) increases from 14.68% to 19.16%. The alkaline nature of ethanolamine greatly neutralizes the acidity of PEDOT:PSS, and plays a role in protecting the anode, leading the stability of the devices to be improved significantly. After being stored for 2000 h, the PCE of ETA-doped PEDOT:PSS devices can maintain 84.2% of the initial value, which is much higher than 67.1% of undoped devices.

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Enhanced photoluminescence of monolayer MoS₂ on stepped gold structure

Yu-Chun Liu(刘玉春), Xin Tan(谭欣), Tian-Ci Shen(沈天赐), and Fu-Xing Gu(谷付星)

2022 (8): 87803-087803. doi: 10.1088/1674-1056/ac657b

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Different MoS₂/Au heterostructures can play an important role in tuning the photoluminescence (PL) and optoelectrical properties of monolayer MoS₂. Previous studies of PL of MoS₂/Au heterostructures were mainly limited to the PL enhancement by using different Au nanostructures and PL quenching of monolayer MoS₂ on flat Au surfaces. Here, we demonstrate the enhanced excitonic PL emissions of monolayer MoS₂/Au heterostructures on Si/SiO₂ substrates. By transferring the continuous monolayer MoS₂ onto a stepped Au structure consisting of 60-nm and 100-nm Au films, the MoS₂/Au-60 and MoS₂/Au-100 heterostructures exhibit enhanced PL emissions, each with a blue-shifted PL peak in comparison with the MoS₂/SiO₂. Furthermore, the PL intensity of MoS₂/Au-60 is about twice larger than that of MoS₂/Au-100. The different enhanced excitonic PL emissions in MoS₂/Au heterostructures can be attributed to the different charge transfer effects modified by the stepped Au structure. This work may provide an insight into the excitonic PL and charge transfer effect of MoS₂ on Au film and yield novel phenomena in MoS₂/Au heterostructures for further study of PL tuning and optoelectrical properties.

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Dual-channel tunable near-infrared absorption enhancement with graphene induced by coupled modes of topological interface states

Zeng-Ping Su(苏增平), Tong-Tong Wei(魏彤彤), and Yue-Ke Wang(王跃科)

2022 (8): 87804-087804. doi: 10.1088/1674-1056/ac6744

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The dual-channel nearly perfect absorption is realized by the coupled modes of topological interface states (TIS) in the near-infrared range. An all-dielectric layered heterostructure composed of photonic crystals (PhC)/graphene/PhC/graphene/PhC on GaAs substrate is proposed to excite the TIS at the interface of adjacent PhC with opposite topological properties. Based on finite element method (FEM) and transfer matrix method (TMM), the dual-channel absorption can be modulated by the periodic number of middle PhC, Fermi level of graphene, and angle of incident light (TE and TM polarizations). Especially, by fine-tuning the Fermi level of graphene around 0.4 eV, the absorption of both channels can be switched rapidly and synchronously. This design is hopefully integrated into silicon-based chips to control light.

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Degradation mechanisms for a-InGaZnO thin-film transistors functioning under simultaneous DC gate and drain biases

Tianyuan Song(宋天源), Dongli Zhang(张冬利), Mingxiang Wang(王明湘), and Qi Shan(单奇)

2022 (8): 88101-088101. doi: 10.1088/1674-1056/ac673e

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Degradation of a-InGaZnO thin-film transistors working under simultaneous DC gate and drain bias stress is investigated, and the corresponding degradation mechanism is proposed and verified. The maximum degradation occurs under the bias stress condition that makes the electric field and electron concentration relatively high at the same time. Trapping of hot electrons in the etching-stop layer under the extended drain electrode is proven to be the underlying mechanism. The observed degradation phenomena, including distortion in the transfer curve on a logarithmic scale and two-slope dependence on gate bias on a linear scale, current crowding in the output curve, and smaller degradation in transfer curves measured under large drain bias, can all be well explained with the proposed degradation mechanism.

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Longitudinal conductivity in ABC-stacked trilayer graphene under irradiating of linearly polarized light

Guo-Bao Zhu(朱国宝), Hui-Min Yang(杨慧敏), and Jie Yang(杨杰)

2022 (8): 88102-088102. doi: 10.1088/1674-1056/ac7205

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We study the effect of linearly polarized light on the band structure and longitudinal conductivity in ABC-stacked trilayer graphene. The linearly polarized light can induce a pair of additional points in ABC-stacked trilayer graphene, where conduct and valence bands touch. The locations of these points are determined by the amplitude of the light. Furthermore, the layer pseudospin polarization can be controlled by the light. When the Fermi energy locates at Dirac points, i.e.， E_f=0, the longitudinal conductivity shows resonance phenomena when the light is present. Away from the Dirac points, the longitudinal conductivity is unchanged as varying E_f for weak light field at larger Fermi energy, and the amplitude of longitudinal conductivity can be controlled by tuning the light field amplitude. Moreover, the effect of linearly polarized light on resonance phenomena in k-cubic Rashba-Dresselhaus system under the irradiating of linearly polarized light is discussed.

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Multiple bottle beams based on metasurface optical field modulation and their capture of multiple atoms

Xichun Zhang(张希纯), Wensheng Fu(付文升), Jinguang Lv(吕金光), Chong Zhang(张崇),Xin Zhao(赵鑫), Weiyan Li(李卫岩), and He Zhang(张贺)

2022 (8): 88103-088103. doi: 10.1088/1674-1056/ac4e06

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Compared to conventional devices, metasurfaces offer the advantages of being lightweight, with planarization and tuning flexibility. This provides a new way to integrate and miniaturize optical systems. In this paper, a metasurface capable of generating multiple bottle beams was designed. Based on the Pancharatnam-Berry (P-B) phase principle, the metasurface lens can accurately control the wavefront by adjusting the aspect ratio of the titanium dioxide nanopillars and the rotation angle. When irradiated by left-handed circularly polarized light with a wavelength of 632.8 nm, the optical system can produce multiple micron bottle beams. Taking two bottle beams as examples, the longitudinal full widths at half-maximum of the optical tweezers can reach 0.85 μ and 1.12 μ, respectively, and the transverse full widths at half-maximum can reach 0.46 μ and 0.6 μ. Also, the number of generated bottle beams can be varied by controlling the size of the annular obstacle. By changing the x-component of the unit rotation angle, the metasurface can also change the shape of the bottle beam — the beam cross-section can be changed from circular to elliptical. This paper also analyzes the trapping of ytterbium atoms by the multi bottle beam acting as optical tweezers. It is found that the multi bottle beam can cool and trap multiple ytterbium atoms.

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Determination of band alignment between GaO_x and boron doped diamond for a selective-area-doped termination structure

Qi-Liang Wang(王启亮), Shi-Yang Fu(付诗洋), Si-Han He(何思翰), Hai-Bo Zhang(张海波),Shao-Heng Cheng(成绍恒), Liu-An Li(李柳暗), and Hong-Dong Li(李红东)

2022 (8): 88104-088104. doi: 10.1088/1674-1056/ac464e

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An n-GaO_x thin film is deposited on a single-crystal boron-doped diamond by RF magnetron sputtering to form the pn heterojunction. The n-GaO_x thin film presents a small surface roughness and a large optical band gap of 4.85 eV. In addition, the band alignment is measured using x-ray photoelectron spectroscopy to evaluate the heterojunction properties. The GaO_x/diamond heterojunction shows a type-II staggered band configuration, where the valence and conduction band offsets are 1.28 eV and 1.93 eV, respectively. These results confirm the feasibility of the use of n-GaO_x as a termination structure for diamond power devices.

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How graph features decipher the soot assisted pigmental energy transport in leaves? A laser-assisted thermal lens study in nanobiophotonics

S Sankararaman

2022 (8): 88201-088201. doi: 10.1088/1674-1056/ac6740

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The paper employs the principles of graph theory in nanobiophotonics, where the soot-assisted intra-pigmental energy transport in leaves is unveiled through the laser-induced thermal lens (TL) technique. Nanofluids with different soot concentrations are sprayed over Lablab purpureus (L) sweet leaves, and the extracted pigments are analyzed. The graph features of the constructed complex network from the TL signal of the samples are analyzed to understand their variations with optical absorbance. Besides revealing the presence of optimum soot concentration that can enhance photosynthesis, the study brings out the potential application of graph features in nanobiophotonics.

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Adaptive semi-empirical model for non-contact atomic force microscopy

Xi Chen(陈曦), Jun-Kai Tong(童君开), and Zhi-Xin Hu(胡智鑫)

2022 (8): 88202-088202. doi: 10.1088/1674-1056/ac6eec

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Non-contact atomic force microscope is a powerful tool to investigate the surface topography with atomic resolution. Here we propose a new approach to estimate the interaction between its tips and samples, which combines a semi-empirical model with density functional theory (DFT) calculations. The generated frequency shift images are consistent with the experiment for mapping organic molecules using CuCO, Cu, CuCl, and CuO_x tips. This approach achieves accuracy close to DFT calculation with much lower computational cost.

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Characterization of topological phase of superlattices in superconducting circuits

Jianfei Chen(陈健菲), Chaohua Wu(吴超华), Jingtao Fan(樊景涛), and Gang Chen(陈刚)

2022 (8): 88501-088501. doi: 10.1088/1674-1056/ac5612

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The recent experimental observation of topological magnon insulator states in a superconducting circuit chain marks a breakthrough for topological physics with qubits, in which a dimerized qubit chain has been realized. Here, we extend such a dimer lattice to superlattice with arbitrary number of qubits in each unit cell in superconducting circuits, which exhibits rich topological properties. Specifically, by considering a quadrimeric superlattice, we show that the topological invariant (winding number) can be effectively characterized by the dynamics of the single-excitation quantum state through time-dependent quantities. Moreover, we explore the appearance and detection of the topological protected edge states in such a multiband qubit system. Finally, we also demonstrate the stable Bloch-like-oscillation of multiple interface states induced by the interference of them. Our proposal can be readily realized in experiment and may pave the way towards the investigation of topological quantum phases and topologically protected quantum information processing.

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Wake-up effect in Hf_0.4Zr_0.6O₂ ferroelectric thin-film capacitors under a cycling electric field

Yilin Li(李屹林), Hui Zhu(朱慧), Rui Li(李锐), Jie Liu(柳杰), Jinjuan Xiang(项金娟), Na Xie(解娜), Zeng Huang(黄增), Zhixuan Fang(方志轩), Xing Liu(刘行), and Lixing Zhou(周丽星)

2022 (8): 88502-088502. doi: 10.1088/1674-1056/ac5977

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We examined the wake-up effect in a TiN/Hf_0.4Zr_0.6O₂/TiN structure. The increased polarization was affected by the cumulative duration of a switched electric field and the single application time of the field during each switching cycle. The space-charge-limited current was stable, indicating that the trap density did not change during the wake-up. The effective charge density in the space-charge region was extracted from capacitance-voltage curves, which demonstrated an increase in free charges at the interface. Based on changing characteristics in these properties, the wake-up effect can be attributed to the redistribution of oxygen vacancies under the electric field.

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A 4×4 metal-semiconductor-metal rectangular deep-ultraviolet detector array of Ga₂O₃ photoconductor with high photo response

Zeng Liu(刘增), Yu-Song Zhi(支钰崧), Mao-Lin Zhang(张茂林), Li-Li Yang(杨莉莉), Shan Li(李山), Zu-Yong Yan(晏祖勇), Shao-Hui Zhang(张少辉), Dao-You Guo(郭道友), Pei-Gang Li(李培刚), Yu-Feng Guo(郭宇锋), and Wei-Hua Tang(唐为华)

2022 (8): 88503-088503. doi: 10.1088/1674-1056/ac597d

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A 4$\times $4 beta-phase gallium oxide ($\beta $-Ga$_{2}$O$_{3}$) deep-ultraviolet (DUV) rectangular 10-fingers interdigital metal-semiconductor-metal (MSM) photodetector array of high photo responsivity is introduced. The Ga$_{2}$O$_{3}$ thin film is prepared through the metalorganic chemical vapor deposition technique, then used to construct the photodetector array via photolithography, lift-off, and ion beam sputtering methods. The one photodetector cell shows dark current of 1.94 pA, photo-to-dark current ratio of 6$\times $10$^{7}$, photo responsivity of 634.15 A$\cdot$W$^{-1}$, specific detectivity of 5.93$\times $10$^{11}$ cm$\cdot$Hz$^{1/2}\cdot$W$^{-1}$ (Jones), external quantum efficiency of 310000%, and linear dynamic region of 108.94 dB, indicating high performances for DUV photo detection. Furthermore, the 16-cell photodetector array displays uniform performances with decent deviation of 19.6% for photo responsivity.

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New insight into the mechanism of DNA polymerase I revealed by single-molecule FRET studies of Klenow fragment

Rokshana Parvin, Qi Jia(贾棋), Jianbing Ma(马建兵), Chunhua Xu(徐春华), Ying Lu(陆颖), Fangfu Ye(叶方富), and Ming Li(李明)

2022 (8): 88701-088701. doi: 10.1088/1674-1056/ac6ed5

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We use single-molecule FRET and newly-developed D-loop techniques to investigate strand displacement activity of Klenow fragment (exo-) of DNA polymerase I in DNA sequences rich in guanine and cytosine (GC) bases. We find that there exist in the FRET traces numerous ascending jumps, which are induced by the backsliding of Klenow fragment on DNA chains. Our measurements show that the probability of backsliding is closely related to the GC-richness and dNTP concentration: increasing the GC-richness leads to an increase in the backsliding probability, and increasing the dNTP concentration however leads to a decrease in the backsliding probability. These results provide a new insight into the mechanism of DNA polymerase I.

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Optical simulation of CsPbI₃/TOPCon tandem solar cells with advanced light management

Min Yue(岳敏), Yan Wang(王燕), Hui-Li Liang(梁会力), and Zeng-Xia Mei (梅增霞)

2022 (8): 88801-088801. doi: 10.1088/1674-1056/ac693d

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Monolithic perovskite/Si tandem solar cells (TSCs) have experienced rapid development in recent years, demonstrating its potential to exceed the Shockley-Queisser limit of single junction Si solar cells. Unlike typical organic-inorganic hybrid perovskite/silicon heterojunction TSCs, here we propose CsPbI₃/TOPCon TSC, which is a promising architecture in consideration of its pleasurable thermal stability and good compatibility with current PERC production lines. The optical performance of CsPbI₃/TOPCon TSCs is simulated by the combination of ray-tracing method and transfer matrix method. The light management of the CsPbI₃/TOPCon TSC begins with the optimization of the surface texture on Si subcell, indicating that a bifacial inverted pyramid with a small bottom angle of rear-side enables a further minimization of the optical losses. Current matching between the subcells, as well as the parasitic absorption loss from the front transparent conductive oxide, is analyzed and discussed in detail. Finally, an optimized configuration of CsPbI₃/TOPCon TSC with a 31.78% power conversion efficiency is proposed. This work provides a practical guidance for approaching high-efficiency perovskite/Si TSCs.

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