Table of contents

14 May 2021, Volume 30 Issue 5 Previous issue    Next issue

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GENERAL

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Exact solution of the Gaudin model with Dzyaloshinsky-Moriya and Kaplan-Shekhtman-Entin-Wohlman-Aharony interactions Fa-Kai Wen(温发楷) and Xin Zhang(张鑫) Chin. Phys. B, 2021, 30 (5):  050201.  DOI: 10.1088/1674-1056/abcf43 Abstract ( 498 )   HTML ( 1 )   PDF (726KB) ( 102 )   We study the exact solution of the Gaudin model with Dzyaloshinsky-Moriya and Kaplan-Shekhtman-Entin-Wohlman-Aharony interactions. The energy and Bethe ansatz equations of the Gaudin model can be obtained via the off-diagonal Bethe ansatz method. Based on the off-diagonal Bethe ansatz solutions, we construct the Bethe states of the inhomogeneous XXX Heisenberg spin chain with the generic open boundaries. By taking a quasi-classical limit, we give explicit closed-form expression of the Bethe states of the Gaudin model. From the numerical simulations for the small-size system, it is shown that some Bethe roots go to infinity when the Gaudin model recovers the U(1) symmetry. Furthermore, it is found that the contribution of those Bethe roots to the Bethe states is a nonzero constant. This fact enables us to recover the Bethe states of the Gaudin model with the U(1) symmetry. These results provide a basis for the further study of the thermodynamic limit, correlation functions, and quantum dynamics of the Gaudin model.

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Closed form soliton solutions of three nonlinear fractional models through proposed improved Kudryashov method Zillur Rahman, M Zulfikar Ali, and Harun-Or Roshid Chin. Phys. B, 2021, 30 (5):  050202.  DOI: 10.1088/1674-1056/abd165 Abstract ( 544 )   HTML ( 1 )   PDF (8041KB) ( 129 )   We introduce a new integral scheme namely improved Kudryashov method for solving any nonlinear fractional differential model. Specifically, we apply the approach to the nonlinear space-time fractional model leading the wave to spread in electrical transmission lines (s-tfETL), the time fractional complex Schrödinger (tfcS), and the space-time M-fractional Schrödinger-Hirota (s-tM-fSH) models to verify the effectiveness of the proposed approach. The implementing of the introduced new technique based on the models provides us with periodic envelope, exponentially changeable soliton envelope, rational rogue wave, periodic rogue wave, combo periodic-soliton, and combo rational-soliton solutions, which are much interesting phenomena in nonlinear sciences. Thus the results disclose that the proposed technique is very effective and straight-forward, and such solutions of the models are much more fruitful than those from the generalized Kudryashov and the modified Kudryashov methods.

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Reputational preference and other-regarding preference based rewarding mechanism promotes cooperation in spatial social dilemmas Huayan Pei(裴华艳), Guanghui Yan(闫光辉), and Huanmin Wang(王焕民) Chin. Phys. B, 2021, 30 (5):  050203.  DOI: 10.1088/1674-1056/abcf9a Abstract ( 491 )   HTML ( 2 )   PDF (1302KB) ( 37 )   To study the incentive mechanisms of cooperation, we propose a preference rewarding mechanism in the spatial prisoner's dilemma game, which simultaneously considers reputational preference, other-regarding preference and the dynamic adjustment of vertex weight. The vertex weight of a player is adaptively adjusted according to the comparison result of his own reputation and the average reputation value of his immediate neighbors. Players are inclined to pay a personal cost to reward the cooperative neighbor with the greatest vertex weight. The vertex weight of a player is proportional to the preference rewards he can obtain from direct neighbors. We find that the preference rewarding mechanism significantly facilitates the evolution of cooperation, and the dynamic adjustment of vertex weight has powerful effect on the emergence of cooperative behavior. To validate multiple effects, strategy distribution and the average payoff and fitness of players are discussed in a microcosmic view.

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Application of non-Hermitian Hamiltonian model in open quantum optical systems Hong Wang(王虹), Yue Qin(秦悦), Jingxu Ma(马晶旭), Heng Shen(申恒), Ying Hu(胡颖), and Xiaojun Jia(贾晓军) Chin. Phys. B, 2021, 30 (5):  050301.  DOI: 10.1088/1674-1056/abda30 Abstract ( 666 )   HTML ( 2 )   PDF (634KB) ( 160 )   Non-Hermitian systems have observed numerous novel phenomena and might lead to various applications. Unlike standard quantum physics, the conservation of energy guaranteed by the closed system is broken in the non-Hermitian system, and the energy can be exchanged between the system and the environment. Here we present a scheme for simulating the dissipative phase transition with an open quantum optical system. The competition between the coherent interaction and dissipation leads to the second-order phase transition. Furthermore, the quantum correlation in terms of squeezing is studied around the critical point. Our work may provide a new route to explore the non-Hermitian quantum physics with feasible techniques in experiments.

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Wave-particle duality relation with a quantum N-path beamsplitter Dong-Yang Wang(王冬阳), Jun-Jie Wu(吴俊杰), Yi-Zhi Wang(王易之), Yong Liu(刘雍), An-Qi Huang(黄安琪), Chun-Lin Yu(于春霖), and Xue-Jun Yang(杨学军) Chin. Phys. B, 2021, 30 (5):  050302.  DOI: 10.1088/1674-1056/abeb0f Abstract ( 603 )   HTML ( 0 )   PDF (779KB) ( 92 )   The wave-particle duality relation derived by Englert sets an upper bound of the extractable information from wave and particle properties in a two-path interferometer. Surprisingly, previous studies demonstrated that the introduction of a quantum beamsplitter in the interferometer could break the limitation of this upper bound, due to interference between wave and particle states. Along the other line, a lot of efforts have been made to generalize this relation from the two-path setup to the N-path case. Thus, it is an interesting question that whether a quantum N-path beamsplitter can break the limitation as well. This paper systemically studies the model of a quantum N-path beamsplitter, and finds that the generalized wave-particle duality relation between interference visibility and path distinguishability is also broken in certain situations. We further study the maximal extractable information's reliance on the interference between wave and particle properties, and derive a quantitative description. We then propose an experimental methodology to verify the break of the limitation. Our work reflects the effect of quantum superposition on wave-particle duality, and exhibits a new aspect of the relation between visibility and path distinguishability in N-path interference. Moreover, it implies the observer's influence on wave-particle duality.

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Dynamical robustness of networks based on betweenness against multi-node attack Zi-Wei Yuan(袁紫薇), Chang-Chun Lv(吕长春), Shu-Bin Si(司书宾), and Dong-Li Duan(段东立) Chin. Phys. B, 2021, 30 (5):  050501.  DOI: 10.1088/1674-1056/abd468 Abstract ( 455 )   HTML ( 10 )   PDF (643KB) ( 99 )   We explore the robustness of a network against failures of vertices or edges where a fraction $f$ of vertices is removed and an overload model based on betweenness is constructed. It is assumed that the load and capacity of vertex $i$ are correlated with its betweenness centrality $B_i$ as $B_i^\theta$ and $(1+\alpha) B_i^\theta$ ($\theta$ is the strength parameter, $\alpha$ is the tolerance parameter). We model the cascading failures following a local load preferential sharing rule. It is found that there exists a minimal $\alpha_{\rm c}$ when $\theta$ is between 0 and 1, and its theoretical analysis is given. The minimal $\alpha_{\rm c}$ characterizes the strongest robustness of a network against cascading failures triggered by removing a random fraction $f$ of vertices. It is realized that the minimal $\alpha_{\rm c}$ increases with the increase of the removal fraction $f$ or the decrease of average degree. In addition, we compare the robustness of networks whose overload models are characterized by degree and betweenness, and find that the networks based on betweenness have stronger robustness against the random removal of a fraction $f$ of vertices.

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Delayed excitatory self-feedback-induced negative responses of complex neuronal bursting patterns Ben Cao(曹奔), Huaguang Gu(古华光), and Yuye Li(李玉叶) Chin. Phys. B, 2021, 30 (5):  050502.  DOI: 10.1088/1674-1056/abcfa9 Abstract ( 584 )   HTML ( 2 )   PDF (3221KB) ( 70 )   In traditional viewpoint, excitatory modulation always promotes neural firing activities. On contrary, the negative responses of complex bursting behaviors to excitatory self-feedback mediated by autapse with time delay are acquired in the present paper. Two representative bursting patterns which are identified respectively to be “Fold/Big Homoclinic” bursting and “Circle/Fold cycle” bursting with bifurcations are studied. For both burstings, excitatory modulation can induce less spikes per burst for suitable time delay and strength of the self-feedback/autapse, because the modulation can change the initial or termination phases of the burst. For the former bursting composed of quiescent state and burst, the mean firing frequency exhibits increase, due to that the quiescent state becomes much shorter than the burst. However, for the latter bursting pattern with more complex behavior which is depolarization block lying between burst and quiescent state, the firing frequency manifests decrease in a wide range of time delay and strength, because the duration of both depolarization block and quiescent state becomes long. Therefore, the decrease degree of spike number per burst is larger than that of the bursting period, which is the cause for the decrease of firing frequency. Such reduced bursting activity is explained with the relations between the bifurcation points of the fast subsystem and the bursting trajectory. The present paper provides novel examples of paradoxical phenomenon that the excitatory effect induces negative responses, which presents possible novel modulation measures and potential functions of excitatory self-feedback/autapse to reduce bursting activities.

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Control of chaos in Frenkel-Kontorova model using reinforcement learning You-Ming Lei(雷佑铭) and Yan-Yan Han(韩彦彦) Chin. Phys. B, 2021, 30 (5):  050503.  DOI: 10.1088/1674-1056/abd74f Abstract ( 604 )   HTML ( 1 )   PDF (5846KB) ( 116 )   It is shown that we can control spatiotemporal chaos in the Frenkel-Kontorova (FK) model by a model-free control method based on reinforcement learning. The method uses Q-learning to find optimal control strategies based on the reward feedback from the environment that maximizes its performance. The optimal control strategies are recorded in a Q-table and then employed to implement controllers. The advantage of the method is that it does not require an explicit knowledge of the system, target states, and unstable periodic orbits. All that we need is the parameters that we are trying to control and an unknown simulation model that represents the interactive environment. To control the FK model, we employ the perturbation policy on two different kinds of parameters, i.e., the pendulum lengths and the phase angles. We show that both of the two perturbation techniques, i.e., changing the lengths and changing their phase angles, can suppress chaos in the system and make it create the periodic patterns. The form of patterns depends on the initial values of the angular displacements and velocities. In particular, we show that the pinning control strategy, which only changes a small number of lengths or phase angles, can be put into effect.

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Numerical investigation on photonic microwave generation by a sole excited-state emitting quantum dot laser with optical injection and optical feedback Zai-Fu Jiang(蒋再富), Zheng-Mao Wu(吴正茂), Wen-Yan Yang(杨文艳), Chun-Xia Hu(胡春霞), Yan-Hong Jin(靳艳红), Zhen-Zhen Xiao(肖珍珍), and Guang-Qiong Xia(夏光琼) Chin. Phys. B, 2021, 30 (5):  050504.  DOI: 10.1088/1674-1056/abd2a8 Abstract ( 485 )   HTML ( 2 )   PDF (1025KB) ( 82 )   Based on three-level exciton model, the enhanced photonic microwave signal generation by using a sole excited-state (ES) emitting quantum dot (QD) laser under both optical injection and optical feedback is numerically studied. Within the range of period-one (P1) dynamics caused by the optical injection, the variations of microwave frequency and microwave intensity with the parameters of frequency detuning and injection strength are demonstrated. It is found that the microwave frequency can be continuously tuned by adjusting the injection parameters, and the microwave intensity can be enhanced by changing the injection strength. Moreover, considering that the generated microwave has a wide linewidth, an optical feedback loop is further employed to compress the linewidth, and the effect of feedback parameters on the linewidth is investigated. It is found that with the increase of feedback strength or delay time, the linewidth is evidently decreased due to the locking effect. However, for the relatively large feedback strength or delay time, the linewidth compression effect becomes worse due to the gradually destroyed P1 dynamics. Besides, through optimizing the feedback parameters, the linewidth can be reduced by up to more than one order of magnitude for different microwave frequencies.

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A 795 nm gain coupled distributed feedback semiconductor laser based on tilted waveguides De-Zheng Ma(马德正), Yong-Yi Chen(陈泳屹), Yu-Xin Lei(雷宇鑫), Peng Jia(贾鹏), Feng Gao(高峰), Yu-Gang Zeng(曾玉刚), Lei Liang(梁磊), Yue Song(宋悦), Chun-Kao Ruan(阮春烤), Xia Liu(刘夏), Li Qin(秦莉), Yong-Qiang Ning(宁永强), and Li-Jun Wang(王立军) Chin. Phys. B, 2021, 30 (5):  050505.  DOI: 10.1088/1674-1056/abdb1d Abstract ( 876 )   HTML ( 0 )   PDF (2361KB) ( 228 )   The 795 nm distributed feedback lasers have great application in pumping the Rb D1 transition. In this paper, in order to realize specific 795 nm lasing, we designed tilted ridge distributed feedback lasers based on purely gain coupled effect induced by periodic current injection windows through changing the angle of the tilted ridge. The fabricated devices were cleaved into 2 mm-cavity-length, including 5 tilted angles. The peak output powers of all devices were above 30 mW. Single longitudinal mode lasing was realized in all tilted Fabry-Perot cavities using periodic current injection windows, with side mode suppression ratio over 30 dB. The total wavelength range covered 8.656 nm at 20 ℃. It was disclosed theoretically and experimentally that the output powers, threshold currents, and central wavelengths of the tilted ridge purely gain coupled DFB lasers were relevant to the tilted angles. The results will be instructive for future design of DFB laser arrays with different central wavelengths.

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Ring artifacts correction based on the projection-field in neutron CT Sheng-Xiang Wang(王声翔), Jie Chen(陈洁), Zhi-Jian Tan(谭志坚), Si-Hao Deng(邓司浩), Yao-Da Wu(吴耀达), Huai-Le Lu(卢怀乐), Shou-Ding Li(李守定), Wei-Chang Chen(陈卫昌), and Lun-Hua He(何伦华) Chin. Phys. B, 2021, 30 (5):  050601.  DOI: 10.1088/1674-1056/abd743 Abstract ( 471 )   HTML ( 2 )   PDF (1618KB) ( 178 )   Ring artifacts will happen mostly when the detector has inconsistent response among the detector channels, and the characteristic produced rings centered in the iso-center in the reconstructed slices inevitably affect the recognition and analysis of the corresponding sample structures in neutron computed tomography (CT). In this work, a ring correction method based on the projection-field (RCP) is proposed, it is a pre-processing method and provides the corrected projection data directly, which is also conducive to efficient data storage and other algorithmic researches. Simulation and physical experiments are performed for verifying the effect of the method, and one of the correction methods based on the image-field is used for comparison. The results demonstrate that the RCP can correct the ring artifacts well without reducing the image resolution or over-correction.

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Improvement of the short-term stability of atomic fountain clock with state preparation by two-laser optical pumping Lei Han(韩蕾), Fang Fang(房芳), Wei-Liang Chen(陈伟亮), Kun Liu(刘昆), Shao-Yang Dai(戴少阳), Ya-Ni Zuo(左娅妮), and Tian-Chu Li(李天初) Chin. Phys. B, 2021, 30 (5):  050602.  DOI: 10.1088/1674-1056/abe22a Abstract ( 441 )   HTML ( 0 )   PDF (653KB) ( 292 )   To improve the signal to noise ratio (SNR) and the short-term stability of cesium atomic fountain clocks, the work of two-laser optical pumping is presented theoretically and experimentally. The short-term stability of the NIM6 fountain clock has been improved by preparing more cold atoms in the $\vert F=4, m_{F}=0\rangle$ clock state with a shortened cycle time. Two $\pi $-polarized laser beams overlapped in the horizontal plane have been applied after launching, one is resonant with $\vert F=4\rangle \to \vert F'=4\rangle$ transition and the other is resonant with $\vert F=3\rangle \to \vert F'=4\rangle$ transition. With optical pumping, the population accumulated in the $\vert m_{F}=0\rangle$ clock state is improved from 11% to 63%, and the detection signal is increased by a factor of 4.2, the SNR of the clock transition probability and the short-term stability are also improved accordingly.

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A 532 nm molecular iodine optical frequency standard based on modulation transfer spectroscopy Feihu Cheng(程飞虎), Ning Jin(金宁), Fenglei Zhang(张风雷), Hui Li(李慧), Yuanbo Du(杜远博), Jie Zhang(张洁), Ke Deng(邓科), and Zehuang Lu(陆泽晃) Chin. Phys. B, 2021, 30 (5):  050603.  DOI: 10.1088/1674-1056/abd754 Abstract ( 525 )   HTML ( 0 )   PDF (1159KB) ( 363 )   We report construction of an iodine-stabilized laser frequency standard at 532 nm based on modulation transfer spectroscopy (MTS) technology with good reproducibility. A frequency stability of $2.5 \times {10}^{-14}$ at 1 s averaging time is achieved, and the frequency reproducibility has a relative uncertainty of ${3.5\times }{10}^{-13}$, demonstrating the great stability of our setup. The systematic uncertainty of the iodine-stabilized laser frequency standard is evaluated, especially the contribution of the residual amplitude modulation (RAM). The contribution of the RAM in MTS cannot be evaluated directly. To solve this problem, we theoretically deduce the MTS signal with RAM under large modulation depth, and prove that the non-symmetric shape of the MTS signal is directly related to the MTS effect. The non-symmetric shape factor $r$ can be calibrated with a frequency comb, and in real experiments, this $r$ value can be obtained by least-squares fitting of the MTS signal, from which we can infer the RAMinduced frequency shift. The full frequency uncertainty is evaluated to be 5.3 kHz (corresponding to a relative frequency uncertainty of ${9.4\times }{10}^{-12})$. The corrected transition frequency has a difference from the BIPM-recommended value of 2 kHz, which is within ${1}\sigma$ uncertainty, proving the validity of our evaluation.

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Phase transition of shocked water up to 6 GPa: Transmittance investigation Lang Wu(吴浪), Yue-Hong Ren(任月虹), Wen-Qiang Liao(廖文强), Xi-Chen Huang(黄曦晨), Fu-Sheng Liu(刘福生), Ming-Jian Zhang(张明建), and Yan-Yun Sun(孙燕云) Chin. Phys. B, 2021, 30 (5):  050701.  DOI: 10.1088/1674-1056/abd691 Abstract ( 575 )   HTML ( 0 )   PDF (584KB) ( 76 )   The phase transition behaviors of the shocked water are investigated by employing an optical transmittance in-situ detection system. Based on the light scattering theory and phase transformation kinetics, the phase transition mechanism of the water under multiple shocks is discussed. The experimental data indicate that the evolution of the transmittance of the shocked water can be broadly divided into three stages: relaxation stage, decline stage, and recovery stage. In the early stage of the phase transition, the new phase particles began to form around the quartz/window interface. It should be mentioned that the water/ice phase boundary seems to move toward the liquid region in one experiment of this work. Due to the new phase core being much smaller than the wavelength of the incident light, the transmittance of the sample within the relaxation stage remains steady. The decline stage can be divided into the rapid descent stage and the slow descent stage in this work, which is considered as the different growth rates of the new phase particle under different shock loadings. The recovery stage is attributed to the emergence of the new phase particles which are bigger than the critical value. However, the influence of the size growth and the population growth of the new phase particles on the transmittance restrict each other, which may be responsible for the phenomenon that the transmittance curve does not return to the initial level.

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High performance infrared detectors compatible with CMOS-circuit process Chao Wang(王超), Ning Li(李宁), Ning Dai(戴宁), Wang-Zhou Shi(石旺舟), Gu-Jin Hu(胡古今), and He Zhu(朱贺) Chin. Phys. B, 2021, 30 (5):  050702.  DOI: 10.1088/1674-1056/abd6fb Abstract ( 601 )   HTML ( 1 )   PDF (511KB) ( 79 )   A type of Si-based blocked impurity band photoelectric detector with a planar architecture is designed and demonstrated by a modified silicon semiconductor processing technique. In this route, multiple ion implantation is utilized to ensure the uniform distribution of the P elements in silicon, and rapid thermal annealing treatment is used to activate the P atoms and reduce damages caused by ion-implantation. The fabricated prototype device exhibits an excellent photoelectric response performance. With a direct current (DC) bias voltage of -2.3 V, the device detectivity to blackbody irradiation is as high as 5×1013cm·Hz1/2/W, which corresponds to a device responsivity of nearly 4.6 A/W, showing their potential applications in infrared detection, infrared astrophysics, and extraterrestrial life science. In particular, the developed device preparation process is compatible with that for the CMOS-circuit, which greatly reduces the manufacturing cost.

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Characterization and application in XRF of HfO2-coated glass monocapillary based on atomic layer deposition Yan-Li Li(李艳丽), Ya-Bing Wang(王亚冰), Wei-Er Lu(卢维尔), Xiang-Dong Kong(孔祥东), Li Han(韩立), and Hui-Bin Zhao(赵慧斌) Chin. Phys. B, 2021, 30 (5):  050703.  DOI: 10.1088/1674-1056/abcfa2 Abstract ( 434 )   HTML ( 0 )   PDF (981KB) ( 295 )   Coating a glass monocapillary x-ray optics with high-density film is a promising way to improve transmission characteristics. For a long time, it has been a challenge to coat a high-density film in the inside of monocapillary with an extremely high length-to-diameter ratio. In this work, HfO$_{2}$ film is deposited on the inner wall of a tapered glass monocapillary with length 9.9 cm, entrance diameter 596.4 μm, and exit diameter 402.3 μm by atomic layer deposition. The coated and uncoated monocapillaries are studied by the transmission process of x-rays with energy from 5 keV to 100 keV and the x-ray fluorescence (XRF) spectra of a Mo sample are detected. Improved transmission characteristics have been obtained for the HfO$_{2}$-coated monocapillary. The energy upper limit of focused x-rays increases from 18.1 keV to 33.0 keV and the ‘penetration halo’ is suppressed to some extent. The XRF spectrum presents two stronger peaks at $\sim 17.4$ keV and $\sim 19.6$ keV which are considered as the characteristic x-rays of Mo K$_{\alpha }$ and Mo K$_{\beta }$. These results reveal that more higher energy x-rays from the W x-ray tube are totally reflected on the inner wall of the HfO$_{2}$-coated glass monocapillary due to the increase of total reflection critical angle. This work is significant for more applications of monocapillary in higher energy x-ray field.

RAPID COMMUNICATION

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Search for topological defect of axionlike model with cesium atomic comagnetometer Hot! Yucheng Yang(杨雨成), Teng Wu(吴腾), Jianwei Zhang(张建玮), and Hong Guo(郭弘) Chin. Phys. B, 2021, 30 (5):  050704.  DOI: 10.1088/1674-1056/abf132 Abstract ( 902 )   HTML ( 2 )   PDF (916KB) ( 726 )   Many terrestrial experiments have been designed to detect domain walls composed of axions or axionlike particles (ALPs), which are promising candidates of dark matter. When the domain wall crosses over the Earth, the pseudoscalar field of ALPs could couple to the atomic spins. Such exotic spin-dependent couplings can be searched for by monitoring the transient-in-time change of the atomic spin precession frequency in the presence of a magnetic field. We propose here a single-species cesium atomic comagnetometer, which measures the spin precession frequencies of atoms in different ground-state hyperfine levels, to eliminate the common-mode magnetic-field variations and search for the exotic non-magnetic couplings solely between protons and ALPs. With the single-species atomic comagnetometer, we experimentally rule out the possibility that the decay constant of the linear pseudoscalar couplings of ALPs to protons is $f_{\rm p}\lesssim 3.71\times 10^{7}~\rm{GeV}$. The advanced system has the potential to constrain the constant to be $f_{\rm p}\lesssim 10.7\times 10^{9}~\rm{GeV}$, promising to improve astrophysical constraint level by at least one order of magnitude. Our system could provide a sensitive detection method for the global network of optical magnetometers to search for exotic physics.

TOPICAL REVIEW—Machine learning in condensed matter physics

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Efficient sampling for decision making in materials discovery Yuan Tian(田原), Turab Lookman, and Dezhen Xue(薛德祯) Chin. Phys. B, 2021, 30 (5):  050705.  DOI: 10.1088/1674-1056/abf12d Abstract ( 592 )   HTML ( 4 )   PDF (3034KB) ( 198 )   Accelerating materials discovery crucially relies on strategies that efficiently sample the search space to label a pool of unlabeled data. This is important if the available labeled data sets are relatively small compared to the unlabeled data pool. Active learning with efficient sampling methods provides the means to guide the decision making to minimize the number of experiments or iterations required to find targeted properties. We review here different sampling strategies and show how they are utilized within an active learning loop in materials science.

SPECIAL TOPIC—Machine learning in condensed matter physics

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Accurate Deep Potential model for the Al-Cu-Mg alloy in the full concentration space Wanrun Jiang(姜万润), Yuzhi Zhang(张与之), Linfeng Zhang(张林峰), and Han Wang(王涵) Chin. Phys. B, 2021, 30 (5):  050706.  DOI: 10.1088/1674-1056/abf134 Abstract ( 904 )   HTML ( 21 )   PDF (787KB) ( 469 )   Combining first-principles accuracy and empirical-potential efficiency for the description of the potential energy surface (PES) is the philosopher's stone for unraveling the nature of matter via atomistic simulation. This has been particularly challenging for multi-component alloy systems due to the complex and non-linear nature of the associated PES. In this work, we develop an accurate PES model for the Al-Cu-Mg system by employing deep potential (DP), a neural network based representation of the PES, and DP generator (DP-GEN), a concurrent-learning scheme that generates a compact set of ab initio data for training. The resulting DP model gives predictions consistent with first-principles calculations for various binary and ternary systems on their fundamental energetic and mechanical properties, including formation energy, equilibrium volume, equation of state, interstitial energy, vacancy and surface formation energy, as well as elastic moduli. Extensive benchmark shows that the DP model is ready and will be useful for atomistic modeling of the Al-Cu-Mg system within the full range of concentration.

GENERAL

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A modified analytical model of the alkali-metal atomic magnetometer employing longitudinal carrier field Chang Chen(陈畅), Yi Zhang(张燚), Zhi-Guo Wang(汪之国), Qi-Yuan Jiang(江奇渊), Hui Luo(罗晖), and Kai-Yong Yang(杨开勇) Chin. Phys. B, 2021, 30 (5):  050707.  DOI: 10.1088/1674-1056/abd7d3 Abstract ( 572 )   HTML ( 0 )   PDF (862KB) ( 148 )   Alkali-metal atomic magnetometers employing longitudinal carrier magnetic field have ultrahigh sensitivity to measure transverse magnetic fields and have been applied in a variety of precise-measurement science and technologies. In practice, the magnetometer response is not rigorously proportional to the measured transverse magnetic fields and the existing fundamental analytical model of this magnetometer is effective only when the amplitudes of the measured fields are very small. In this paper, we present a modified analytical model to characterize the practical performance of the magnetometer more definitely. We find out how the longitudinal magnetization of the alkali metal atoms vary with larger transverse fields. The linear-response capacity of the magnetometer is determined by these factors: the amplitude and frequency of the longitudinal carrier field, longitudinal and transverse spin relaxation time of the alkali spins and rotation frequency of the transverse fields. We give a detailed and rigorous theoretical derivation by using the perturbation-iteration method and simulation experiments are conducted to verify the validity and correctness of the proposed modified model. This model can be helpful for measuring larger fields more accurately and configuring a desirable magnetometer with proper linear range.

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Blind parameter estimation of pseudo-random binary code-linear frequency modulation signal based on Duffing oscillator at low SNR Ke Wang(王珂), Xiaopeng Yan(闫晓鹏), Ze Li(李泽), Xinhong Hao(郝新红), and Honghai Yu(于洪海) Chin. Phys. B, 2021, 30 (5):  050708.  DOI: 10.1088/1674-1056/abd75f Abstract ( 576 )   HTML ( 0 )   PDF (1125KB) ( 52 )   Conventional parameter estimation methods for pseudo-random binary code-linear frequency modulation (PRBC-LFM) signals require prior knowledge, are computationally complex, and exhibit poor performance at low signal-to-noise ratios (SNRs). To overcome these problems, a blind parameter estimation method based on a Duffing oscillator array is proposed. A new relationship formula among the state of the Duffing oscillator, the pseudo-random sequence of the PRBC-LFM signal, and the frequency difference between the PRBC-LFM signal and the periodic driving force signal of the Duffing oscillator is derived, providing the theoretical basis for blind parameter estimation. Methods based on amplitude method, short-time Fourier transform method, and power spectrum entropy method are used to binarize the output of the Duffing oscillator array, and their performance is compared. The pseudo-random sequence is estimated using Duffing oscillator array synchronization, and the carrier frequency parameters are obtained by the relational expressions and characteristics of the difference frequency. Simulation results show that this blind estimation method overcomes limitations in prior knowledge and maintains good parameter estimation performance up to an SNR of -35 dB.

ATOMIC AND MOLECULAR PHYSICS

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Configuration interaction study on low-lying states of AlCl molecule Xiao-Ying Ren(任笑影), Zhi-Yu Xiao(肖志宇), Yong Liu(刘勇), and Bing Yan(闫冰) Chin. Phys. B, 2021, 30 (5):  053101.  DOI: 10.1088/1674-1056/abd46a Abstract ( 560 )   HTML ( 0 )   PDF (857KB) ( 48 )   High-level ab initio calculations of the Λ-S states for aluminum monoiodide (AlCl) molecule are performed by utilizing the explicitly correlated multireference configuration interaction (MRCI-F12) method. The Davidson correction and scalar relativistic correction are investigated in the calculations. Based on the calculation by the MRCI-F12 method, the spin-orbit coupling (SOC) effect is investigated with the state-interacting technique. The adiabatic potential energy curves (PECs) of the 13 Λ-S states and 24 Ω states are calculated. The spectroscopic constants of bound states are determined, which are in accordance with the results of the available experimental and theoretical studies. Finally, the transition properties of 0+(2)-X0+, 1(1)-X0+, and 1(2)-X0+ transitions are predicted, including the transition dipole moments (TDMs), Franck-Condon factors (FCFs), and the spontaneous radiative lifetimes.

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Transition parameters of Li-like ions (Z=7-11) in dense plasmas Xiang-Fu Li(李向富), Li-Ping Jia(贾利平), Hong-Bin Wang(王宏斌), and Gang Jiang(蒋刚) Chin. Phys. B, 2021, 30 (5):  053102.  DOI: 10.1088/1674-1056/abea80 Abstract ( 548 )   HTML ( 1 )   PDF (705KB) ( 64 )   The energy levels, transition energies, transition probabilities, weighted oscillator strengths, and line strengths of Li-like ions ($Z=7$-11) in dense plasmas are investigated in this work. The relativistic effects and electron correlation effects are described by the MCDHF method. The ion sphere model is applied to include the dense plasma screening effect. The ground configuration $\text{1s}^2\text{2s}$ and the excited $\text{1s}^2\text{2p}$, $\text{1s}^2{3}l$ ($l=0$-2) are considered. The configuration sets are enlarged until $n=7$ where the calculated energy levels have converged. The critical free electron densities of $\text{1s}^2\text{3d}$ states are estimated. Except for $\text{1s}^2\text{3s}$-$\text{1s}^2\text{3p}$ transitions, the transition energies for $\Delta n = 0$ increase, and for $\Delta n \neq 0$ decrease with increasing free electron densities. For $\text{1s}^2\text{3s}$-$\text{1s}^2\text{3p}$ transitions, the spectra show blue-shift at lower free electron densities and red-shift at higher free electron densities, and the energy level crossing phenomens are observed at higher free electron densities.

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Anisotropic exciton Stark shift in hemispherical quantum dots Shu-Dong Wu(吴曙东) Chin. Phys. B, 2021, 30 (5):  053201.  DOI: 10.1088/1674-1056/abd472 Abstract ( 564 )   HTML ( 1 )   PDF (1296KB) ( 104 )   The exciton Stark shift and polarization in hemispherical quantum dots (HQDs) each as a function of strength and orientation of applied electric field are theoretically investigated by an exact diagonalization method. A highly anisotropic Stark redshift of exciton energy is found. As the electric field is rotated from Voigt to Faraday geometry, the redshift of exciton energy monotonically decreases. This is because the asymmetric geometric shape of the hemispherical quantum dot restrains the displacement of the wave function to the higher orbital state in response to electric field along Faraday geometry. A redshift of hole energy is found all the time while a transition of electron energy from this redshift to a blueshift is found as the field is rotated from Voigt to Faraday geometry. Taking advantage of the diminishing of Stark effect along Faraday geometry, the hemispherical shapes can be used to improve significantly the radiative recombination efficiency of the polar optoelectronic devices if the strong internal polarized electric field is along Faraday geometry.

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High-precision three-dimensional Rydberg atom localization in a four-level atomic system Hengfei Zhang(张恒飞), Jinpeng Yuan(元晋鹏), Lirong Wang(汪丽蓉), Liantuan Xiao(肖连团), and Suo-tang Jia(贾锁堂) Chin. Phys. B, 2021, 30 (5):  053202.  DOI: 10.1088/1674-1056/abd46f Abstract ( 510 )   HTML ( 1 )   PDF (1243KB) ( 277 )   Rydberg atoms have been widely investigated due to their large size, long radiative lifetime, huge polarizability and strong dipole-dipole interactions. The position information of Rydberg atoms provides more possibilities for quantum optics research, which can be obtained under the localization method. We study the behavior of three-dimensional (3D) Rydberg atom localization in a four-level configuration with the measurement of the spatial optical absorption. The atomic localization precision depends strongly on the detuning and Rabi frequency of the involved laser fields. A 100% probability of finding the Rydberg atom at a specific 3D position is achieved with precision of ～0.031λ. This work demonstrates the possibility for achieving the 3D atom localization of the Rydberg atom in the experiment.

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Stable quantum interference enabled by coexisting detuned and resonant STIRAPs Dan Liu(刘丹), Yichun Gao(高益淳), Jianqin Xu(许建琴), and Jing Qian(钱静) Chin. Phys. B, 2021, 30 (5):  053701.  DOI: 10.1088/1674-1056/abe0c5 Abstract ( 612 )   HTML ( 1 )   PDF (1584KB) ( 71 )   Inspired by a recent experiment [Phys. Rev. Lett. 122 253201(2019)] that an unprecedented quantum interference was observed in the way of stimulated Raman adiabatic passage (STIRAP) due to the coexisting resonant- and detuned-STIRAPs, we comprehensively study this effect. Our results uncover the scheme robustness towards any external-field fluctuations coming from laser intensity noise and imperfect resonance condition, as well as the persistence of high-contrast interference pattern even when more nearby excited levels are involved. We verify that an auxiliary dynamical phase accumulated in hold time caused by the presence of the quasi-dark state in detuned-STIRAP can sensitively manipulate the visibility and frequency of the interference pattern, representing a new hallmark to measure the hyperfine energy accurately. The robust stability of the scheme comes from the intrinsic superiority embedded in the STIRAP mechanism that preserves the coherence of population transfer, which promises a remarkable performance of quantum interference in a practical implementation.

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Setup of a dipole trap for all-optical trapping Miao Wang(王淼), Zheng Chen(陈正), Yao Huang(黄垚), Hua Guan(管桦), and Ke-Lin Gao(高克林) Chin. Phys. B, 2021, 30 (5):  053702.  DOI: 10.1088/1674-1056/abd767 Abstract ( 635 )   HTML ( 4 )   PDF (810KB) ( 256 )   Micromotion induced by the radio-frequency field contributes greatly to the systematic frequency shifts of optical frequency standards. Although different strategies for mitigating this effect have been proposed, trapping ions optically has the potential to provide a generic solution to the elimination of micromotion. This could be achieved by trapping a single ion in the dipole trap composed of a highpower laser field. Here, we present the setup of the dipole trap composed of a 532 nm laser at a power of 10 W aiming to optically trap a single 40Ca+ and we observe an AC-Stark shift of the fluorescence spectrum line of ～22 MHz caused by the 532 nm dipole beam. The beam waist of the dipole laser is several microns, which would provide a dipole potential strong enough for all-optical trapping of a single 40Ca+ ion.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

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Handwritten digit recognition based on ghost imaging with deep learning Xing He(何行), Sheng-Mei Zhao(赵生妹), and Le Wang(王乐) Chin. Phys. B, 2021, 30 (5):  054201.  DOI: 10.1088/1674-1056/abd2a5 Abstract ( 573 )   HTML ( 2 )   PDF (850KB) ( 234 )   We present a ghost handwritten digit recognition method for the unknown handwritten digits based on ghost imaging (GI) with deep neural network, where a few detection signals from the bucket detector, generated by the cosine transform speckle, are used as the characteristic information and the input of the designed deep neural network (DNN), and the output of the DNN is the classification. The results show that the proposed scheme has a higher recognition accuracy (as high as 98% for the simulations, and 91% for the experiments) with a smaller sampling ratio (say 12.76%). With the increase of the sampling ratio, the recognition accuracy is enhanced. Compared with the traditional recognition scheme using the same DNN structure, the proposed scheme has slightly better performance with a lower complexity and non-locality property. The proposed scheme provides a promising way for remote sensing.

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Absorption interferometer of two-sided cavity Miao-Di Guo(郭苗迪) and Hong-Mei Li(李红梅) Chin. Phys. B, 2021, 30 (5):  054202.  DOI: 10.1088/1674-1056/abdea4 Abstract ( 373 )   HTML ( 2 )   PDF (874KB) ( 80 )   We propose a scheme in which an arbitrary incidence can be made perfectly reflected/transmitted with a phase modulator. We analyze the variation of intracavity field as well as output field with closed-loop phase φ1 of the control fields and relative phase φ2 of the probe beams. With two phases, medium absorption and light interference can be controlled so that photon escape from the cavity can be manipulated, thus an intensity switching based on phase modulation can be realized. And the condition for perfect transmitter or reflector is obtained. Then based on the transmission/reflection analysis, the total absorption of this system can be investigated. Therefore our scheme can be used as an absorption interferometer to explore the optical absorption in some complicated system. The state delay of the output light intensity, which is dependent on φ1 or φ2, can be applied in the realization of quantum phase gate and subtle wave filter. And based on this scheme, we implement the state transfer between perfect transmitter/reflector and non-perfect coherent photon absorber via relative-phase modulation.

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A pressure-calibration method of wavelength modulation spectroscopy in sealed microbial growth environment Kun-Yang Wang(王坤阳), Jie Shao(邵杰), Li-Gang Shao(邵李刚), Jia-Jin Chen(陈家金), Gui-Shi Wang(王贵师), Kun Liu(刘琨), and Xiao-Ming Gao(高晓明) Chin. Phys. B, 2021, 30 (5):  054203.  DOI: 10.1088/1674-1056/abda32 Abstract ( 502 )   HTML ( 1 )   PDF (677KB) ( 210 )   A new pressure-calibration method for calibrating the reduction of second harmonic (2f) amplitude caused by pressure broadening effect in sealed microbial growth environment is present. The new method combines with linewidth compensation and modulation depth compensation and makes the 2f amplitude accurately retrieve metabolic CO2 in microbial growth. In order to verify the method, a simulation experiment is developed, in which the increasing CO2 concentration leads to the increasing pressure. Comparing with the relation between the traditional 2f amplitude and gas concentration, there is a monotonous relation between the calibrated 2f amplitude and CO2 concentration, particularly, a linear relation is present when the CO2 concentration is replaced with the CO2 particle number. In terms of microbial measurement, the growth of Escherichia coli is measured, and the culture bottle is sealed during the microbial growth process. The experimental results show that, comparing to the microbial growth retrieved by traditional 2f amplitude, the calibrated 2f amplitude can accurately retrieve microbial growth in sealed environment.

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Zinc-oxide/PDMS-clad tapered fiber saturable absorber for passively mode-locked erbium-doped fiber laser F D Muhammad, S A S Husin, E K Ng, K Y Lau, C A C Abdullah, and M A Mahdi Chin. Phys. B, 2021, 30 (5):  054204.  DOI: 10.1088/1674-1056/abd76e Abstract ( 515 )   HTML ( 2 )   PDF (2024KB) ( 99 )   We propose and demonstrate a passively mode-locked erbium-doped fiber laser (EDFL) based on zinc-oxide/polydimethylsiloxane (ZnO/PDMS) saturable absorber (SA) that evanescently interacts with the light on a tapered fiber. The ZnO/PDMS composite is coated on the whole surface of the tapered fiber to guarantee the maximum efficiency of the SA device, with a measured insertion loss of 0.87 dB and a modulation depth of 6.4%. The proposed laser can generate soliton mode-locking operation at a threshold power of 33.07 mW. The generated output pulse yields a repetition rate and pulse width of 9.77 MHz and 1.03 ps, respectively. These results indicate that the proposed ZnO/PDMS-clad tapered fiber could be useful as an efficient, compatible, and low-cost SA device for ultrafast laser applications.

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Generation of cavity-birefringence-dependent multi-wavelength bright-dark pulse pair in a figure-eight thulium-doped fiber laser Xiao-Fa Wang(王小发), Dong-Xin Liu(刘东鑫), Hui-Hui Han(韩慧慧), and Hong-Yang Mao(毛红炀) Chin. Phys. B, 2021, 30 (5):  054205.  DOI: 10.1088/1674-1056/abd68f Abstract ( 578 )   HTML ( 2 )   PDF (1180KB) ( 60 )   We experimentally demonstrated a stable multi-wavelength bright-dark pulse pair in a mode-locked thulium-doped fiber laser (TDFL). The nonlinear polarization rotation (NPR) and nonlinear optical loop mirror (NOLM) were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation. By incorporating different lengths of high birefringence polarization-maintaining fiber (PMF), the fiber laser could operate stably in a multi-wavelength emission state. Compared with the absence of the PMF, the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright-dark pulse pair.

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Dissipative Kerr solitons in optical microresonators with Raman effect and third-order dispersion Chaohua Wu(吴超华), Zhiwei Fang(方致伟), Jintao Fan(樊景涛), Gang Chen(陈刚), and Ya Cheng(程亚) Chin. Phys. B, 2021, 30 (5):  054206.  DOI: 10.1088/1674-1056/abd15f Abstract ( 583 )   HTML ( 0 )   PDF (711KB) ( 224 )   Using the mean-field normalized Lugiato-Lefever equation, we theoretically investigate the dynamics of cavity soliton and comb generation in the presence of Raman effect and the third-order dispersion. Both of them can induce the temporal drift and frequency shift. Based on the moment analysis method, we analytically obtain the temporal and frequency shift, and the results agree with the direct numerical simulation. Finally, the compensation and enhancement of the soliton spectral between the Raman-induced self-frequency shift and soliton recoil are predicted. Our results pave the way for further understanding the soliton dynamics and spectral characteristics, and providing an effective route to manipulate frequency comb.

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Narrow-band high-transmittance birefringent filter and its application in wide color gamut display Chi Zhang(张弛), Rui Niu(牛瑞), Wenjuan Li(李文娟), Xiaoshuai Li(李小帅), Hongmei Ma(马红梅), and Yubao Sun(孙玉宝) Chin. Phys. B, 2021, 30 (5):  054207.  DOI: 10.1088/1674-1056/abd471 Abstract ( 548 )   HTML ( 4 )   PDF (737KB) ( 215 )   We propose a narrow-band birefringent filter and its application in wide color gamut. The birefringent filter consists of five phase retarders and two polarizers, and it has both narrow band and high transmittance. In the experiment, we fabricate the birefringent filter using quartz phase retarders and polarizers, and apply it in serval different displays. The color gamuts of displays are enhanced more than 30%NTSC (National Television System Committee), and the widest color gamuts that have been obtained are 126%NTSC in liquid crystal displays and 138%NTSC in organic light-emitting devices. Moreover, the deep blue light in spectrum of display can be reduced using the birefringent filter. The birefringent filter can be an efficient element to achieve wide color gamut display.

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Controllable four-wave mixing response in a dual-cavity hybrid optomechanical system Lei Shang(尚蕾), Bin Chen(陈彬), Li-Li Xing(邢丽丽), Jian-Bin Chen(陈建宾), Hai-Bin Xue(薛海斌), and Kang-Xian Guo(郭康贤) Chin. Phys. B, 2021, 30 (5):  054209.  DOI: 10.1088/1674-1056/abd695 Abstract ( 457 )   HTML ( 1 )   PDF (706KB) ( 206 )   We systematically investigate the four-wave mixing (FWM) spectrum in a dual-cavity hybrid optomechanical system, which is made up of one optical cavity with an ensemble of two-level atoms and another with a mechanical oscillator. In this work, we propose that the hybrid dual-cavity optomechanical system can be employed as a highly sensitive mass sensor due to the fact that the FWM spectrum generated in this system has a narrow spectral width and the intensity of the FWM can be easily tuned by controlling the coupling strength (cavity-cavity, atom-cavity). More fascinatingly, the dual-cavity hybrid optomechanical system can also be used as an all-optical switch in view of the easy on/off control of FWM signals by adjusting the atom-pump detuning to be positive or negative. The proposed schemes have great potential applications in quantum information processing and highly sensitive detection.

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Experimental analysis of interface contact behavior using a novel image processing method Jingyu Han(韩靖宇), Zhijun Luo(罗治军), Yuling Zhang(张玉玲), and Shaoze Yan(阎绍泽) Chin. Phys. B, 2021, 30 (5):  054601.  DOI: 10.1088/1674-1056/abd696 Abstract ( 576 )   HTML ( 2 )   PDF (2354KB) ( 358 )   The spatial and temporal evolution of real contact area of contact interface with loads is a challenge. It is generally believed that there is a positive linear correlation between real contact area and normal load. However, with the development of measuring instruments and methods, some scholars have found that the growth rate of real contact area will slow down with the increase of normal load under certain conditions, such as large-scale interface contact with small roughness surface, which is called the nonlinear phenomenon of real contact area. At present, there is no unified conclusion on the explanation of this phenomenon. We set up an experimental apparatus based on the total reflection principle to verify this phenomenon and analyze its mechanism. An image processing method is proposed, which can be used to quantitative analysis micro contact behaviors on macro contact phenomenon. The weighted superposition method is used to identify micro contact spots, to calculate the real contact area, and the color superimposed image is used to identify micro contact behaviors. Based on this method, the spatiotemporal evolution mechanism of real contact area nonlinear phenomena is quantitatively analyzed. Furthermore, the influence of nonlinear phenomenon of real contact area on the whole loading and unloading process is analyzed experimentally. It is found that the effects of fluid between contact interface, normal load amplitude and initial contact state on contact behavior cannot be ignored in large-scale interface contact with small roughness surface.

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Improved nonlinear parabolized stability equations approach for hypersonic boundary layers Shaoxian Ma(马绍贤), Yi Duan(段毅), Zhangfeng Huang(黄章峰), and Shiyong Yao(姚世勇) Chin. Phys. B, 2021, 30 (5):  054701.  DOI: 10.1088/1674-1056/abd2a3 Abstract ( 517 )   HTML ( 1 )   PDF (1323KB) ( 62 )   The nonlinear parabolized stability equations (NPSEs) approach is widely used to study the evolution of disturbances in hypersonic boundary layers owing to its high computational efficiency. However, divergence of the NPSEs will occur when disturbances imposed at the inlet no longer play a leading role or when the nonlinear effect becomes very strong. Two major improvements are proposed here to deal with the divergence of the NPSEs. First, all disturbances are divided into two types: dominant waves and non-dominant waves. Disturbances imposed at the inlet or playing a leading role are defined as dominant waves, with all others being defined as non-dominant waves. Second, the streamwise wavenumbers of the non-dominant waves are obtained using the phase-locked method, while those of the dominant waves are obtained using an iterative method. Two reference wavenumbers are introduced in the phase-locked method, and methods for calculating them for different numbers of dominant waves are discussed. Direct numerical simulation (DNS) is performed to verify and validate the predictions of the improved NPSEs in a hypersonic boundary layer on an isothermal swept blunt plate. The results from the improved NPSEs approach are in good agreement with those of DNS, whereas the traditional NPSEs approach is subject to divergence, indicating that the improved NPSEs approach exhibits greater robustness.

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Impact mechanism of gas temperature in metal powder production via gas atomization Peng Wang(汪鹏), Jing Li(李静), Xin Wang(王欣), Bo-Rui Du(杜博睿), Shi-Yuan Shen(申世远), Xue-Yuan Ge(葛学元), and Miao-Hui Wang(王淼辉) Chin. Phys. B, 2021, 30 (5):  054702.  DOI: 10.1088/1674-1056/abd75e Abstract ( 526 )   HTML ( 1 )   PDF (5562KB) ( 323 )   This paper aims at studying the influence mechanism of gas temperatures (300 K, 400 K, 500 K, and 600 K) on gas atomization by simulating the integral atomization process of the close-coupled nozzle in vacuum induction gas atomization (VIGA). The primary atomization is simulated by the volume of fluid (VOF) approach, and the second atomization is studied by the discrete phase model (DPM) combined with the instability breakage model. The results show that, at an increased gas temperature, the influences of gas-liquid contact angle and gas temperature in the recirculation zone on the primary atomization are virtually negligible. However, increasing the gas temperature will increase the gas-liquid relative velocity near the recirculation zone and decrease the melt film thickness, which are the main reasons for the reduced mass median diameter (MMD, d50) of primary atomized droplets. During the secondary atomization, increasing the gas temperature from 300 K to 600 K results in an increase in the droplet dispersion angle, which is beneficial to the formation of spherical metal powder. In addition, increasing the gas temperature, the positive effect of gas-liquid relative velocity increase on droplets refinement overweighs the negative influence of the GMR decrease, resulting in the reduced MMD and diameter distribution interval. From the analysis of the atomization mechanism, the increase in atomization efficiency caused by increasing the temperature of the atomizing gas, including primary atomization and secondary atomization, is mainly due to the increase in the gas drag force difference between the inner and outer sides of the annular liquid film.

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Numerical simulation on partial coalescence of a droplet with different impact velocities Can Peng(彭灿), Xianghua Xu(徐向华), and Xingang Liang(梁新刚) Chin. Phys. B, 2021, 30 (5):  054703.  DOI: 10.1088/1674-1056/abd7dd Abstract ( 579 )   HTML ( 1 )   PDF (917KB) ( 207 )   Partial coalescence is a complicated flow phenomenon. In the present study, the coalescence process is simulated with the volume of fluid (VOF) method. The numerical results reveal that a downward high-velocity region plays a significant role in partial coalescence. The high-velocity region pulls the droplet downward continuously which is an important factor for the droplet turning into a prolate shape and the final pinch-off. The shift from partial coalescence to full coalescence is explained based on the droplet shape before the pinch-off. With the droplet impact velocity increasing, the droplet shape will get close to a sphere before the pinch-off. When the shape gets close enough to a sphere, the partial coalescence shifts to full coalescence. The effect of film thickness on the coalescence process is also investigated. With large film thickness, partial coalescence happens, while with small film thickness, full coalescence happens. In addition, the results indicate that the critical droplet impact velocity increases with the increase of surface tension coefficient but decreases with the increase of viscosity and initial droplet diameter. And there is a maximum critical Weber number with the increase of surface tension coefficient and initial droplet diameter.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Quasi-delta negative ions density of Ar/O2 inductively coupled plasma at very low electronegativity Shu-Xia Zhao(赵书霞) Chin. Phys. B, 2021, 30 (5):  055201.  DOI: 10.1088/1674-1056/abd16a Abstract ( 571 )   HTML ( 1 )   PDF (7838KB) ( 107 )   One of the novel phenomena of Ar/O2 inductively coupled plasma, the delta negative ions density profile is discovered by the fluid simulation at very low electronegativity. The anions delta is found to be formed by the collaboration of successive plasma transport phases. The plasma transport itself is affected by the delta, exhibiting many new phenomena. A new type of Helmholtz equation is devised to mathematically explain the delta forming mechanism. For revealing the physics behind, a revised spring oscillator dynamic equation has been constructed according to the Helmholtz equation, in a relevant paper [Zhao S X and Li J Z (2021) Chin. Phys. B 30 055202]. The investigation about the anions delta distribution is a nice prediction of new phenomenon in low temperature electronegative plasmas, waiting for the validation of related experiments.

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Delta distribution of electronegative plasma predicted by reformed “spring oscillator” dynamic equation with dispersing force Shu-Xia Zhao(赵书霞) and Jing-Ze Li(李京泽) Chin. Phys. B, 2021, 30 (5):  055202.  DOI: 10.1088/1674-1056/abd166 Abstract ( 505 )   HTML ( 1 )   PDF (627KB) ( 96 )   In our relevant paper [Zhao S X (2021) Chin. Phys. B 30 055201], a delta distribution of negative ions is given by fluid simulation and preliminarily explained by decomposed anions transport equation. In the present work, first, the intrinsic connection between the electropositive plasma transport equation and spring oscillator dynamic equation is established. Inspired by this similarity, reformed “spring oscillator” equation with dispersing instead of restoring force that gives quasi-delta solution is devised according to the math embodied in the anion equation, which is of potential significance to the disciplines of atomic physics and astronomy as well. For solving the “diffusion confusion” the physics that determines the delta profile within the continuity equation is explored on the basis that recombination loss source term plays the role of drift flux, which is applicable for fluid model of low temperature plasma, but not the ordinary fluid dynamics. Besides, the math and physics revealed in this work predict that the ratio of recombination or attachment (for electrons) frequency versus the species diffusion coefficient is a very important parameter in determining the delta distribution, as it acts as the acceleration of object, according to the reformed oscillator equation. With this theory, the analogous delta profile of electrons density in the famous drift and ambi-polar diffusion heating mechanism of electronegative capacitively coupled plasma is interpreted.

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Energy behavior of Boris algorithm Abdullah Zafar and Majid Khan Chin. Phys. B, 2021, 30 (5):  055203.  DOI: 10.1088/1674-1056/abd161 Abstract ( 402 )   HTML ( 1 )   PDF (3576KB) ( 135 )   Boris numerical scheme due to its long-time stability, accuracy and conservative properties has been widely applied in many studies of magnetized plasmas. Such algorithms conserve the phase space volume and hence provide accurate charge particle orbits. However, this algorithm does not conserve the energy in some special electromagnetic configurations, particularly for long simulation times. Here, we empirically analyze the energy behavior of Boris algorithm by applying it to a 2D autonomous Hamiltonian. The energy behavior of the Boris method is found to be strongly related to the integrability of our Hamiltonian system. We find that if the invariant tori is preserved under Boris discretization, the energy error can be bounded for an exponentially long time, otherwise the said error will show a linear growth. On the contrary, for a non-integrable Hamiltonian system, a random walk pattern has been observed in the energy error.

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Nonlinear propagation of an intense Laguerre-Gaussian laser pulse in a plasma channel Mingping Liu(刘明萍), Zhen Zhang(张震), and Suhui Deng(邓素辉) Chin. Phys. B, 2021, 30 (5):  055204.  DOI: 10.1088/1674-1056/abd68c Abstract ( 448 )   HTML ( 1 )   PDF (880KB) ( 124 )   The nonlinear propagation of an intense Laguerre-Gaussian (LG) laser pulse in a parabolic preformed plasma channel is analyzed by means of the variational method. The evolution equation of the spot size is derived including the effects of relativistic self-focusing, preformed channel focusing, and ponderomotive self-channeling. The parametric conditions of the LG laser pulse and plasma channel for propagating with constant spot size, periodically focusing and defocusing oscillation, catastrophic focusing, and solitary waves are obtained. Compared with the laser pulse with fundamental Gaussian (FG) mode, it is found that the effect of vacuum diffraction is reduced by half and the effects of relativistic and wakefield focusing are decreased by a quarter due to the hollow transverse intensity profile of the LG laser pulse, while the effect of channel focusing is the same order of magnitude with that of the FG laser pulse. Thus, the matched condition for the intense LG laser pulse with constant spot size is released obviously, while the parameters of the laser and plasma for the existence of solitary waves nearly coincide with those of the FG laser pulse.

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Effect of pressure and space between electrodes on the deposition of SiNxHy films in a capacitively coupled plasma reactor Meryem Grari, CifAllah Zoheir, Yasser Yousfi, and Abdelhak Benbrik Chin. Phys. B, 2021, 30 (5):  055205.  DOI: 10.1088/1674-1056/abd2a4 Abstract ( 504 )   HTML ( 1 )   PDF (975KB) ( 181 )   The fluid model, also called the macroscopic model, is commonly used to simulate low temperature and low pressure radiofrequency plasma discharges. By varying the parameters of the model, numerical simulation allows us to study several cases, providing us the physico-chemical information that is often difficult to obtain experimentally. In this work, using the fluid model, we employ numerical simulation to show the effect of pressure and space between the reactor electrodes on the fundamental properties of silicon plasma diluted with ammonia and hydrogen. The results show the evolution of the fundamental characteristics of the plasma discharge as a function of the variation of the pressure and the distance between the electrodes. By examining the pressure-distance product in a range between 0.3 Torr 2.7 cm and 0.7 Torr 4 cm, we have determined the optimal pressure-distance product that allows better deposition of hydrogenated silicon nitride (SiNxHy) films which is 0.7 Torr 2.7 cm.

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Observation of trapped and passing runaway electrons by infrared camera in the EAST tokamak Yong-Kuan Zhang(张永宽), Rui-Jie Zhou(周瑞杰), Li-Qun Hu(胡立群), Mei-Wen Chen(陈美文), Yan Chao(晁燕), Jia-Yuan Zhang(张家源), and Pan Li(李磐) Chin. Phys. B, 2021, 30 (5):  055206.  DOI: 10.1088/1674-1056/abd758 Abstract ( 598 )   HTML ( 1 )   PDF (1276KB) ( 77 )   In EAST, synchrotron radiation is emitted by runaway electrons in the infrared band, which can be observed by infrared cameras. This synchrotron radiation is mainly emitted by passing runaway electrons with tens of MeV energy. A common feature of radiation dominated by passing runaway electrons is that it is strongest on the high field side. However, the deeply trapped runaway electrons cannot reach the high field side in principle. Therefore, in this case, the high field side radiation is expected to be weak. This paper reports for the first time that the synchrotron radiation from trapped runaway electrons dominates that from passing runaway electrons and is identifiable in an image. Although the synchrotron radiation dominated by trapped runaway electrons can be observed in experiment, the proportion of trapped runaway electrons is very low.

REVIEW

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Review on ionization and quenching mechanisms of Trichel pulse Anbang Sun(孙安邦), Xing Zhang(张幸), Yulin Guo(郭雨林), Yanliang He(何彦良), and Guanjun Zhang(张冠军) Chin. Phys. B, 2021, 30 (5):  055207.  DOI: 10.1088/1674-1056/abd75d Abstract ( 477 )   HTML ( 2 )   PDF (2392KB) ( 222 )   Trichel pulse is a kind of pulsed mode in negative DC corona discharge, which has attracted significant attention because of its considerable applications in industry. Over eighty years, plenty of effort including simulations and experiments has been spent to reveal the ionization and quenching mechanisms of Trichel pulse. By revisiting and summarizing the basic characteristics and well-accepted ionization and quenching mechanisms, this review provides a basic understanding and the current status of Trichel pulse.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Mechanical property and deformation mechanism of gold nanowire with non-uniform distribution of twinned boundaries: A molecular dynamics simulation study Qi-Xin Xiao(肖启鑫), Zhao-Yang Hou(侯兆阳), Chang Li(李昌), and Yuan Niu(牛媛) Chin. Phys. B, 2021, 30 (5):  056101.  DOI: 10.1088/1674-1056/abd162 Abstract ( 522 )   HTML ( 2 )   PDF (1236KB) ( 95 )   The mechanical property and deformation mechanism of twinned gold nanowire with non-uniform distribution of twinned boundaries (TBs) are studied by the molecular dynamics (MD) method. It is found that the twin boundary spacing (TBS) has a great effect on the strength and plasticity of the nanowires with uniform distribution of TBs. And the strength enhances with the decrease of TBS, while its plasticity declines. For the nanowires with non-uniform distribution of TBs, the differences in distribution among different TBSs have little effect on the Young's modulus or strength, and the compromise in strength appears. But the differences have a remarkable effect on the plasticity of twinned gold nanowire. The twinned gold nanowire with higher local symmetry ratio has better plasticity. The initial dislocations always form in the largest TBS and the fracture always appears at or near the twin boundaries adjacent to the smallest TBS. Some simulation results are consistent with the experimental results.

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A rational design of bimetallic PdAu nanoflowers as efficient catalysts for methanol oxidation reaction Jinyang Liu(刘锦阳), Min Wu(武敏), Xinyi Yang(杨新一), Juan Ding(丁娟), Weiwei Lei(类伟巍), and Yongming Sui(隋永明) Chin. Phys. B, 2021, 30 (5):  056102.  DOI: 10.1088/1674-1056/abda2f Abstract ( 444 )   HTML ( 1 )   PDF (1998KB) ( 151 )   Methanol fuel cells have been intensively developed as clean and high-efficiency energy conversion system due to their high efficiency and low emission of pollutants. Here, we developed a simple aqueous synthetic method to prepare bimetallic PdAu nanoflowers catalysts for methanol oxidation reaction (MOR) in alkaline environment. Their composition can be directly tuned by changing the ratio between Pd and Au precursors. Compared with commercial Pd/C catalyst, all of the PdAu nanoflowers catalysts show the enhanced catalytic activity and durability. In particular, the PdAu nanoflowers specific activity reached 0.72 mA/cm2, which is 14 times that of commercial Pd/C catalyst. The superior MOR activity could be attributed to the unique porous structure and the shift of the d-band center of Pd.

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Water and nutrient recovery from urine: A lead up trail using nano-structured In2S3 photo electrodes R Jayakrishnan, T R Sreerev, and Adith Varma Chin. Phys. B, 2021, 30 (5):  056103.  DOI: 10.1088/1674-1056/abd169 Abstract ( 447 )   HTML ( 1 )   PDF (1241KB) ( 60 )   Developments of economic systems are critical for bio-regenerative life support systems in manned space missions. In this work we report on the feasibility of using two direct sunlight powered processes sequentially for the recovery of water and nutrients from urine. The work presents experimental evidence on nutrient and water recovery achieved using the proto-type designed and developed. We report the design and testing of a solar still which would serve on the nutrient recovery front. The cooled condensate from the solar still is fed into a solar powered electrolysis unit where nano-structured indium sulphide (In2S3) thin films coated over fluorine doped tin oxide (SnO2:F) substrate serve as one of the working electrodes. The electrolysis takes place in the absence of an electrolyte which manifests as a technical achievement of our work. Our results show that the COD level in the recycled water is very low. The In2S3 photo-electrodes are stable without any physical damage after the process.

SPECIAL TOPIC—Ion beam modification of materials and applications

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Structure and luminescence of a-plane GaN on r-plane sapphire substrate modified by Si implantation Lijie Huang(黄黎杰), Lin Li(李琳), Zhen Shang(尚震), Mao Wang(王茂), Junjie Kang(康俊杰), Wei Luo(罗巍), Zhiwen Liang(梁智文), Slawomir Prucnal, Ulrich Kentsch, Yanda Ji(吉彦达), Fabi Zhang(张法碧), Qi Wang(王琦), Ye Yuan(袁冶), Qian Sun(孙钱), Shengqiang Zhou(周生强), and Xinqiang Wang(王新强) Chin. Phys. B, 2021, 30 (5):  056104.  DOI: 10.1088/1674-1056/abd76a Abstract ( 734 )   HTML ( 1 )   PDF (1426KB) ( 245 )   We show the structural and optical properties of non-polar a-plane GaN epitaxial films modified by Si ion implantation. Upon gradually raising Si fluences from 5×1013 cm-2 to 5×1015 cm-2, the n-type dopant concentration gradually increases from 4.6×1018 cm-2 to 4.5×1020 cm-2, while the generated vacancy density accordingly raises from 3.7×1013 cm-2 to 3.8×1015 cm-2. Moreover, despite that the implantation enhances structural disorder, the epitaxial structure of the implanted region is still well preserved which is confirmed by Rutherford backscattering channeling spectrometry measurements. The monotonical uniaxial lattice expansion along the a direction (out-of-plane direction) is observed as a function of fluences till 1×1015 cm-2, which ceases at the overdose of 5×1015 cm-2 due to the partial amorphization in the surface region. Upon raising irradiation dose, a yellow emission in the as-grown sample is gradually quenched, probably due to the irradiation-induced generation of non-radiative recombination centers.

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Evolution of ion-irradiated point defect concentration by cluster dynamics simulation Shuaishuai Feng(冯帅帅), Shasha Lv(吕沙沙), Liang Chen(陈良), and Zhengcao Li(李正操) Chin. Phys. B, 2021, 30 (5):  056105.  DOI: 10.1088/1674-1056/abf102 Abstract ( 652 )   HTML ( 1 )   PDF (633KB) ( 177 )   The relationship between ions irradiation and the induced microstructures (point defects, dislocations, clusters, etc.) could be better analyzed and explained by simulation. The mean field rate theory and cluster dynamics are used to simulate the effect of implanted Fe on the point defects concentration quantitatively. It is found that the depth distribution of point defect concentration is relatively gentle than that of damage calculated by SRIM software. Specifically, the damage rate and point defect concentration increase by 1.5 times and 0.6 times from depth of 120 nm to 825 nm, respectively. With the consideration of implanted Fe ions, which effectively act as interstitial atoms at the depth of high ion implantation rate, the vacancy concentration Cv decreases significantly after reaching the peak value, while the interstitial atom concentration Ci increases significantly after decline of the previous stage. At the peak depth of ion implantation, Cv dropped by 86%, and Ci increased by 6.2 times. Therefore, the implanted ions should be considered into the point defects concentration under high dose of heavy ion irradiation, which may help predict the concentration distribution of defect clusters, further analyzing the evolution behavior of solute precipitation.

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Optical spectroscopy study of damage evolution in 6H-SiC by H$_{2}^{ + }$ implantation Yong Wang(王勇), Qing Liao(廖庆), Ming Liu(刘茗), Peng-Fei Zheng(郑鹏飞), Xinyu Gao(高新宇), Zheng Jia(贾政), Shuai Xu(徐帅), and Bing-Sheng Li(李炳生) Chin. Phys. B, 2021, 30 (5):  056106.  DOI: 10.1088/1674-1056/abe9a7 Abstract ( 618 )   HTML ( 2 )   PDF (1911KB) ( 210 )   Lattice defects induced by ion implantation into SiC have been widely investigated in the decades by various techniques. One of the non-destructive techniques suitable to study the lattice defects in SiC is the optical characterization. In this work, confocal Raman scattering spectroscopy and photoluminescence spectrum have been used to study the effects of 134-keV H$_{2}^{ + }$ implantation and thermal treatment in the microstructure of 6H-SiC single crystal. The radiation-induced changes in the microstructure were assessed by integrating Raman-scattering peaks intensity and considering the asymmetry of Raman-scattering peaks. The integrated intensities of Raman scattering spectroscopy and photoluminescence spectrum decrease with increasing the fluence. The recovery of the optical intensities depends on the combination of the implantation temperature and the annealing temperature with the thermal treatment from 700 ℃ to 1100 ℃. The different characterizations of Raman scattering spectroscopy and photoluminescence spectrum are compared and discussed in this study.

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Effect of helium concentration on irradiation damage of Fe-ion irradiated SIMP steel at 300 ℃ and 450 ℃ Zhen Yang(杨振), Junyuan Yang(杨浚源), Qing Liao(廖庆), Shuai Xu(徐帅), and Bingsheng Li(李炳生) Chin. Phys. B, 2021, 30 (5):  056107.  DOI: 10.1088/1674-1056/abd6f9 Abstract ( 662 )   HTML ( 2 )   PDF (2393KB) ( 164 )   SIMP steel is newly developed fully martensitic steel for lead-cooled fast reactors and accelerator-driven systems. It is important to evaluate its radiation resistance via high flux neutron irradiation, where dense He atoms can be formed via (n, α) transmutation reaction. Co-irradiation with Fe and He ions, instead of neutron, was performed. Specimens were irradiated with 6.4-MeV Fe ions to the damage dose of 5 dpa at a depth of 600 nm. Three different helium injection ratios of 60-appm He/dpa (dpa: displacements per atom), 200-appm He/dpa and 600-appm He/dpa at a depth of 600 nm, were performed. Two different irradiation temperatures of 300 ℃ and 450 ℃ were carried out. The effect of helium concentration on the microstructure of Fe-irradiated SIMP steel was investigated. Microstructural damage was observed using transmission electron microscopy. The formed dislocation loops and bubbles depended on the helium injection ratio and irradiation temperature. Lots of dislocation loops and helium bubbles were homogeneously distributed at 300 °C, but not at 450 °C. The causes of observed effects are discussed.

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Effect of tellurium (Te4+) irradiation on microstructure and associated irradiation-induced hardening Hefei Huang(黄鹤飞), Jizhao Liu(刘继召), Guanhong Lei(雷冠虹), Ondrej Muránsky, Tao Wei, and Mihail Ionescu Chin. Phys. B, 2021, 30 (5):  056108.  DOI: 10.1088/1674-1056/abf039 Abstract ( 636 )   HTML ( 1 )   PDF (3151KB) ( 208 )   The GH3535 alloy samples were irradiated using 15-MeV Te4+ ions at 650 °C to a dose of 0.5, 3.0, 10, and 20 dpa, respectively. The Te atoms distribution and microstructure evolution were examined by electron probe microanalysis (EPMA) and transmission electron microscopy (TEM). The nano-indenter was then used to measure the nano-hardness changes of samples before and after irradiation. TEM results showed the formation of dislocation loops in the irradiated samples. Their mean diameters increase with the increase of irradiation dose and tends to be saturated when irradiation dose exceeds 10 dpa. The ratio of yield strength increments calculated by dispersed barrier hardening (DBH) model is basically consistent with that of nano-hardness increments measured by nano-indenter. In addition, the relationship between the nano-hardness increments and dpa for the GH3535 alloy irradiated by Te ions has been revealed in the study.

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Corrosion behavior of high-level waste container materials Ti and Ti-Pd alloy under long-term gamma irradiation in Beishan groundwater Qianglin Wei(魏强林), Yuhong Li(李玉红), Yanliang Huang(黄彦良), Dongyan Yang(杨冬燕), Bo Yang(杨波), and Yibao Liu(刘义保) Chin. Phys. B, 2021, 30 (5):  056109.  DOI: 10.1088/1674-1056/abf03b Abstract ( 743 )   HTML ( 1 )   PDF (3435KB) ( 235 )   Titanium and titanium-palladium alloys are important potential materials for nuclear waste container, which will endure both intense γ-irradiation and groundwater erosion. Therefore, it is very important to investigate the corrosion behavior of the container materials. In this research, the cumulative dose effect of TA8-1 type titanium-palladium alloy (TA8-1) and TA2-type pure titanium (TA2) under γ-irradiation was studied based on the geological disposal of nuclear wastes. The irradiation experiments were performed at room temperature using 60Co gamma sources with a 5.0-kGy·h-1 intensity for 40, 80 or 160 days, respectively. The pH value and conductivity of Beishan groundwater were investigated. The results showed that the pH value changed from alkaline (8.22) to acidic (2.46 for TA8-1 and 2.44 for TA2), while the un-irradiated solution remained alkaline (8.17 for TA8-1 and 8.20 for TA2) after 160 days. With the increase of irradiation dose, the conductivity increases rapidly and then tends to become stable, which indicates that the titanium dioxide corrosion layer formed on the surface of the sample surface effectively prevents further corrosion. Meanwhile, XRD and SEM-EDS analysis results show that the main components of corrosion products are TiO2 and TiO. The titanium on the surface of the sample is oxidized, resulting in slight uneven local corrosion. The results show that TA8-1 and TA2 are suitable to be used as candidate materials for high-level waste (HLW) disposal containers due to their excellent performance under long-term and high-dose irradiation corrosion.

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Degradation of β-Ga2O3 Schottky barrier diode under swift heavy ion irradiation Wen-Si Ai(艾文思), Jie Liu(刘杰), Qian Feng(冯倩), Peng-Fei Zhai(翟鹏飞), Pei-Pei Hu(胡培培), Jian Zeng(曾健), Sheng-Xia Zhang(张胜霞), Zong-Zhen Li(李宗臻), Li Liu(刘丽), Xiao-Yu Yan(闫晓宇), and You-Mei Sun(孙友梅) Chin. Phys. B, 2021, 30 (5):  056110.  DOI: 10.1088/1674-1056/abf107 Abstract ( 678 )   HTML ( 2 )   PDF (1008KB) ( 219 )   The electrical characteristics and microstructures of β-Ga2O3 Schottky barrier diode (SBD) devices irradiated with swift heavy ions (2096 MeV Ta ions) have been studied. It was found that β-Ga2O3 SBD devices showed the reliability degradation after irradiation, including turn-on voltage Von, on-resistance Ron, ideality factor n, and the reverse leakage current density Jr. In addition, the carrier concentration of the drift layer was decreased significantly and the calculated carrier removal rates were 5×106-1.3×107 cm-1. Latent tracks induced by swift heavy ions were observed visually in the whole β-Ga2O3 matrix. Furthermore, crystal structure of tracks was amorphized completely. The latent tracks induced by Ta ions bombardments were found to be the reason for the decrease in carrier mobility and carrier concentration. Eventually, these defects caused the degradation of electrical characteristics of the devices. In terms of the carrier removal rates, the β-Ga2O3 SBD devices were more sensitive to swift heavy ions irradiation than SiC and GaN devices.

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Influence of temperature and alloying elements on the threshold displacement energies in concentrated Ni-Fe-Cr alloys Shijun Zhao(赵仕俊) Chin. Phys. B, 2021, 30 (5):  056111.  DOI: 10.1088/1674-1056/abf10d Abstract ( 571 )   HTML ( 3 )   PDF (3382KB) ( 187 )   Concentrated solid-solution alloys (CSAs) have demonstrated promising irradiation resistance depending on their compositions. Under irradiation, various defects can be produced. One of the most important parameters characterizing the defect production and the resulting defect number is the threshold displacement energies (Ed). In this work, we report the results of Ed values in a series of Ni-Fe-Cr concentrated solid solution alloys through molecular dynamics (MD) simulations. Based on several different empirical potentials, we show that the differences in the Ed values and its angular dependence are mainly due to the stiffness of the potential in the intermediate regime. The influences of different alloying elements and temperatures on Ed values in different CSAs are further evaluated by calculating the defect production probabilities. Our results suggest a limited influence of alloying elements and temperature on Ed values in concentrated alloys. Finally, we discuss the relationship between the primary damage and Ed values in different alloys. Overall, this work presents a thorough study on the Ed values in concentrated alloys, including the influence of empirical potentials, their angular dependence, temperature dependence, and effects on primary defect production.

SPECIAL TOPIC—Active matters physics

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Phoretic self-assembly of active colloidal molecules Lijie Lei(雷李杰), Shuo Wang(王硕), Xinyuan Zhang(张昕源), Wenjie Lai(赖文杰), Jinyu Wu(吴晋宇), and Yongxiang Gao(高永祥) Chin. Phys. B, 2021, 30 (5):  056112.  DOI: 10.1088/1674-1056/abc2bd Abstract ( 610 )   HTML ( 1 )   PDF (3360KB) ( 206 )   We simulate the self-assembly of active colloidal molecules from binary mixtures of spherical particles using a Brownian dynamics algorithm. These particles interact via phoretic interactions, which are determined by two independently tunable parameters, surface activity and surface mobility. In systems composed of equal-size particles, we observe the formation of colloidal molecules with well-defined coordination numbers and spatial arrangement, which also display distinct dynamic functions, such as resting, translating, and rotating. By changing the size ratio to 2:1 between the two species, we further observe the formation of colloidal molecules with new structures arising from breaking the size symmetry. By tuning the mutual interactions between the smaller species via their surface mobility, we are able to control their spacing as well as the coordination number of the colloidal molecules. This study highlights the importance of tuning surface parameters and size asymmetry in controlling the structure and the active dynamics of colloidal molecules.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Negative compressibility property in hinging open-cell Kelvin structure Meng Ma(马梦), Xiao-Qin Zhou(周晓勤), Hao Liu(刘浩), and Hao-Cheng Wang(王浩成) Chin. Phys. B, 2021, 30 (5):  056201.  DOI: 10.1088/1674-1056/abd6f7 Abstract ( 515 )   HTML ( 2 )   PDF (3289KB) ( 32 )   A new three-dimensional (3D) cellular model based on hinging open-cell Kelvin structure is proposed for its negative compressibility property. It is shown that this model has adjustable compressibility and does exhibit negative compressibility for some certain conformations. And further study shows that the images of compressibility are symmetrical about the certain lines, which indicates that the mechanical properties of the model in the three axial directions are interchangeable and the model itself has a certain geometric symmetry. A comparison of the Kelvin model with its anisotropic form with the dodecahedron model shows that the Kelvin model has stronger negative compressibility property in all three directions. Therefore, a new and potential method to improve negative compressibility property can be derived by selecting the system type with lower symmetry and increasing the number of geometric parameters.

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High-pressure elastic anisotropy and superconductivity of hafnium: A first-principles calculation Cheng-Bin Zhang(张成斌), Wei-Dong Li(李卫东), Ping Zhang(张平), and Bao-Tian Wang(王保田) Chin. Phys. B, 2021, 30 (5):  056202.  DOI: 10.1088/1674-1056/abd6f6 Abstract ( 475 )   HTML ( 2 )   PDF (6472KB) ( 73 )   The elastic anisotropy and superconductivity upon hydrostatic compression of α, ω, and β Hf are investigated using first-principle methods. The results of elastic anisotropies show that they increase with increasing pressure for α and ω phases, while decrease upon compression for β phase. The calculated superconducting transition temperatures are in excellent agreement with experiments. Electron-phonon coupling constants (λ) are increasing with pressure for α and ω phases, while decreasing for β phase. For β phase, the large values of λ are mainly due to the obvious TA1 soft mode. Under further compression, the TA1 soft vibrational mode will disappear gradually.

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Negative thermal expansion in NbF3 and NbOF2: A comparative theoretical study Mingyue Zhang(张明月), Chunyan Wang(王春艳), Yinuo Zhang(张一诺), Qilong Gao(高其龙), and Yu Jia(贾瑜) Chin. Phys. B, 2021, 30 (5):  056501.  DOI: 10.1088/1674-1056/abe376 Abstract ( 523 )   HTML ( 2 )   PDF (3813KB) ( 248 )   Thermal expansion control is always an obstructive factor and challenging in high precision engineering field. Here, the negative thermal expansion of NbF3 and NbOF2 was predicted by first-principles calculation with density functional theory and the quasi-harmonic approximation (QHA). We studied the total charge density, thermal vibration, and lattice dynamic to investigate the thermal expansion mechanism. We found that the presence of O induced the relatively strong covalent bond in NbOF2, thus weakening the transverse vibration of F and O in NbOF2, compared with the case of NbF3. In this study, we proposed a way to tailor negative thermal expansion of metal fluorides by introducing the oxygen atoms. The present work not only predicts two NTE compounds, but also provides an insight on thermal expansion control by designing chemical bond type.

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Two-dimensional PC3 as a promising anode material for potassium-ion batteries: First-principles calculations Chun Zhou(周淳), Junchao Huang(黄俊超), and Xiangmei Duan(段香梅) Chin. Phys. B, 2021, 30 (5):  056801.  DOI: 10.1088/1674-1056/abf10e Abstract ( 482 )   HTML ( 2 )   PDF (1330KB) ( 73 )   With the diversified development of the battery industry, potassium-ion batteries (PIBs) have aroused widespread interest due to their safety and high potassium reserves on earth. However, the lack of suitable anode materials limits their development and application to a certain extent. Based on first-principles calculations, we investigate the possibility of using PC3 monolayer as the anode material for PIBs. PC3 sheet has excellent electrical properties and meets the prerequisite of anode materials. The storage capacity of potassium is as high as 1200 mAh·g-1, which is better than many other reported potassium-ion anode materials. In addition, the outstanding advantages of PC3 sheet, such as low diffusion barrier and moderate open-circuit voltage, make it a potential anode candidate for PIBs.

RAPID COMMUNICATION

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NBN-doped nanographene embedded with five- and seven-membered rings on Au(111) surface Hot! Huan Yang(杨欢), Yun Cao(曹云), Yixuan Gao(高艺璇), Yubin Fu(付钰彬), Li Huang(黄立), Junzhi Liu(刘俊治), Xinliang Feng(冯新亮), Shixuan Du(杜世萱), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2021, 30 (5):  056802.  DOI: 10.1088/1674-1056/abeede Abstract ( 875 )   HTML ( 3 )   PDF (796KB) ( 339 )   Nanographenes (NGs) can be embedded with predesigned dopants or nonhexagonal rings to tailor the electronic properties and provide ideal platforms to study the unique physical and chemical properties. Here, we report the on-surface synthesis of NBN-doped NG embedded with five- and seven-membered rings (NBN-575-NG) on Au(111) from a oligophenylene precursor preinstalled with a NBN unit and a heptagonal ring. Scanning tunneling microscopy and non-contact atomic force microscopy images elucidate the intramolecular cyclodehydrogenation and the existence of the five- and seven-membered rings. Scanning tunneling spectroscopy spectra reveal that the NBN-575-NG is a semiconductor, which agrees with the density functional theory calculation results on a freestanding NBN-575-NG with the same structure. This work provides a feasible approach for the on-surface synthesis of novel NGs containing non-hexagonal rings.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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First-principles investigation of the valley and electrical properties of carbon-doped α-graphyne-like BN sheet Bo Chen(陈波), Xiang-Qian Li(李向前), Lin Xue(薛林), Yan Han(韩燕), Zhi Yang(杨致), and Long-Long Zhang(张龙龙) Chin. Phys. B, 2021, 30 (5):  057101.  DOI: 10.1088/1674-1056/abddac Abstract ( 563 )   HTML ( 1 )   PDF (2093KB) ( 222 )   Based on ab initio density functional theory calculations, we demonstrate that two carbon-doped boron nitride analog of α-graphyne structures, B3C2N3 and BC6N monolayers, are two-dimensional direct wide band gap semiconductors, and there are two inequivalent valleys in the vicinities of the vertices of their hexagonal Brillouin zones. Besides, B3C2N3 and BC6N monolayers exhibit relatively high carrier mobilities, and their direct band gap feature is robust against the biaxial strain. More importantly, the energetically most favorable B3C2N3 and BC6N bilayers also have direct wide band gaps, and valley polarization could be achieved by optical helicity. Finally, we show that BC6N monolayer might have high efficiency in photo-splitting reactions of water, and a vertical van der Waals heterostructure with a type-Ⅱ energy band alignment could be designed using B3C2N3 and BC6N monolayers. All the above-mentioned characteristics make B3C2N3 and BC6N monolayers, bilayers, and their heterostructures recommendable candidates for applications in valleytronic devices, metal-free photocatalysts, and photovoltaic cells.

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First-principles calculations of K-shell x-ray absorption spectra for warm dense ammonia Zi Li(李孜), Wei-Jie Li(李伟节), Cong Wang(王聪), Dafang Li(李大芳), Wei Kang(康炜), Xian-Tu He(贺贤土), and Ping Zhang(张平) Chin. Phys. B, 2021, 30 (5):  057102.  DOI: 10.1088/1674-1056/abdb1b Abstract ( 394 )   HTML ( 1 )   PDF (865KB) ( 209 )   The x-ray absorption spectroscopy is a powerful tool for the detection of thermodynamic conditions and atomic structures on warm dense matter. Here, we perform first-principles molecular dynamics and x-ray absorption spectrum calculations for warm dense ammonia, which is one of the major constituents of Uranus and Neptune. The nitrogen K-shell x-ray absorption spectrum (XAS) is determined along the Hugoniot curve, and it is found that the XAS is a good indicator of the prevailing thermodynamic conditions. The atomic structures at these conditions are ascertained. Results indicate that the ammonia could dissociate to NHx (x=0, 1, or 2) fragments and form nitrogen clusters, and the ratios of these products change with varying conditions. The contributions to the XAS from these products show quite different characteristics, inducing the significant change of XAS along the Hugoniot curve. Further model simulations imply that the distribution of the peak position of atomic XAS is the dominant factor affecting the total XAS.

SPECIAL TOPIC—Machine learning in condensed matter physics

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Quantitative structure-plasticity relationship in metallic glass: A machine learning study Yicheng Wu(吴义成), Bin Xu(徐斌), Yitao Sun(孙奕韬), and Pengfei Guan(管鹏飞) Chin. Phys. B, 2021, 30 (5):  057103.  DOI: 10.1088/1674-1056/abdda5 Abstract ( 640 )   HTML ( 4 )   PDF (724KB) ( 177 )   The lack of the long-range order in the atomic structure challenges the identification of the structural defects, akin to dislocations in crystals, which are responsible for predicting plastic events and mechanical failure in metallic glasses (MGs). Although vast structural indicators have been proposed to identify the structural defects, quantitatively gauging the correlations between these proposed indicators based on the undeformed configuration and the plasticity of MGs upon external loads is still lacking. Here, we systematically analyze the ability of these indicators to predict plastic events in a representative MG model using machine learning method. Moreover, we evaluate the influences of coarse graining method and medium-range order on the predictive power. We demonstrate that indicators relevant to the low-frequency vibrational modes reveal the intrinsic structural characteristics of plastic rearrangements. Our work makes an important step towards quantitative assessments of given indicators, and thereby an effective identification of the structural defects in MGs.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Investigation of electronic, elastic, and optical properties of topological electride Ca3Pb via first-principles calculations Chang Sun(孙畅), Xin-Yu Cao(曹新宇), Xi-Hui Wang(王西惠), Xiao-Le Qiu(邱潇乐), Zheng-Hui Fang(方铮辉), Yu-Jie Yuan(袁宇杰), Kai Liu(刘凯), and Xiao Zhang(张晓) Chin. Phys. B, 2021, 30 (5):  057104.  DOI: 10.1088/1674-1056/abec38 Abstract ( 507 )   HTML ( 3 )   PDF (2014KB) ( 106 )   Electrides are unique materials with the anionic electrons confined to the interstitial sites, expecting important applications in various areas. In this work, the electronic structure and detailed physical properties of topological electride Ca3Pb are studied theoretically. By comparing the crystal structures and band structures of Ca3Pb and Ca3PbO, we find that after removing O2- ions from Ca3PbO, the remaining electrons are confined in the vacancies of the Ca6 octahedra centers, playing the role as anions and forming an additional energy band compared with that of Ca3Pb. These interstitial electrons partially result in the low work function of Ca3Pb. Moreover, the calculated mechanic properties imply that Ca3Pb has a strong brittleness. In addition, the dielectric functions and optical properties of Ca3Pb are also analyzed.

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Tunable valley filter efficiency by spin-orbit coupling in silicene nanoconstrictions Yi-Jian Shi(施一剑), Yuan-Chun Wang(王园春), and Peng-Jun Wang(汪鹏君) Chin. Phys. B, 2021, 30 (5):  057201.  DOI: 10.1088/1674-1056/abcf35 Abstract ( 557 )   HTML ( 1 )   PDF (897KB) ( 59 )   Valley filter is a promising device for producing valley polarized current in graphene-like two-dimensional honeycomb lattice materials. The relatively large spin-orbit coupling in silicene contributes to remarkable quantum spin Hall effect, which leads to distinctive valley-dependent transport properties compared with intrinsic graphene. In this paper, quantized conductance and valley polarization in silicene nanoconstrictions are theoretically investigated in quantum spin-Hall insulator phase. Nearly perfect valley filter effect is found by aligning the gate voltage in the central constriction region. However, the valley polarization plateaus are shifted with the increase of spin-orbit coupling strength, accompanied by smooth variation of polarization reversal. Our findings provide new strategies to control the valley polarization in valleytronic devices.

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High-responsivity solar-blind photodetector based on MOCVD-grown Si-doped β-Ga2O3 thin film Yu-Song Zhi(支钰崧), Wei-Yu Jiang(江为宇), Zeng Liu(刘增), Yuan-Yuan Liu(刘媛媛), Xu-Long Chu(褚旭龙), Jia-Hang Liu(刘佳航), Shan Li(李山), Zu-Yong Yan(晏祖勇), Yue-Hui Wang(王月晖), Pei-Gang Li(李培刚), Zhen-Ping Wu(吴真平), and Wei-Hua Tang(唐为华) Chin. Phys. B, 2021, 30 (5):  057301.  DOI: 10.1088/1674-1056/abe37a Abstract ( 589 )   HTML ( 3 )   PDF (2894KB) ( 250 )   Si-doped β-Ga2O3 films are fabricated through metal-organic chemical vapor deposition (MOCVD). Solar-blind ultraviolet (UV) photodetector (PD) based on the films is fabricated by standard photolithography, and the photodetection properties are investigated. The results show that the photocurrent increases to 11.2 mA under 200 μW·cm-2 254 nm illumination and ±20 V bias, leading to photo-responsivity as high as 788 A·W-1. The Si-doped β-Ga2O3-based PD is promised to perform solar-blind photodetection with high performance.

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Ferroelectric effect and equivalent polarization charge model of PbZr0.2Ti0.8O3 on AlGaN/GaN MIS-HEMT Yao-Peng Zhao(赵垚澎), Chong Wang(王冲), Xue-Feng Zheng(郑雪峰), Xiao-Hua Ma(马晓华), Ang Li(李昂), Kai Liu(刘凯), Yun-Long He(何云龙), Xiao-Li Lu(陆小力) and Yue Hao(郝跃) Chin. Phys. B, 2021, 30 (5):  057302.  DOI: 10.1088/1674-1056/abd469 Abstract ( 716 )   HTML ( 3 )   PDF (977KB) ( 212 )   PbZr0.2Ti0.8O3 (PZT) gate insulator with the thickness of 30 nm is grown by pulsed laser deposition (PLD) in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs). The ferroelectric effect of PZT AlGaN/GaN MIS-HEMT is demonstrated. The polarization charge in PZT varies with different gate voltages. The equivalent polarization charge model (EPCM) is proposed for calculating the polarization charge and the concentration of two-dimensional electron gas (2DEG). The threshold voltage (Vth) and output current density (IDS) can also be obtained by the EPCM. The theoretical values are in good agreement with the experimental results and the model can provide a guide for the design of the PZT MIS-HEMT. The polarization charges of PZT can be modulated by different gate-voltage stresses and the Vth has a regulation range of 4.0 V. The polarization charge changes after the stress of gate voltage for several seconds. When the gate voltage is stable or changes at high frequency, the output characteristics and the current collapse of the device remain stable.

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A super-junction SOI-LDMOS with low resistance electron channel Wei-Zhong Chen(陈伟中), Yuan-Xi Huang(黄元熙), Yao Huang(黄垚), Yi Huang(黄义), and Zheng-Sheng Han(韩郑生) Chin. Phys. B, 2021, 30 (5):  057303.  DOI: 10.1088/1674-1056/abe374 Abstract ( 647 )   HTML ( 10 )   PDF (1674KB) ( 175 )   A novel super-junction LDMOS with low resistance channel (LRC), named LRC-LDMOS based on the silicon-on-insulator (SOI) technology is proposed. The LRC is highly doped on the surface of the drift region, which can significantly reduce the specific on resistance (Ron,sp) in forward conduction. The charge compensation between the LRC, N-pillar, and P-pillar of the super-junction are adjusted to satisfy the charge balance, which can completely deplete the whole drift, thus the breakdown voltage (BV) is enhanced in reverse blocking. The three-dimensional (3D) simulation results show that the BV and Ron,sp of the device can reach 253 V and 15.5 mΩ·cm2, respectively, and the Baliga's figure of merit (FOM=BV2/Ron,sp) of 4.1 MW/cm2 is achieved, breaking through the silicon limit.

DATA PAPER

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High-throughput identification of one-dimensional atomic wires and first principles calculations of their electronic states Feng Lu(卢峰), Jintao Cui(崔锦韬), Pan Liu(刘盼), Meichen Lin(林玫辰), Yahui Cheng(程雅慧), Hui Liu(刘晖), Weichao Wang(王卫超), Kyeongjae Cho, and Wei-Hua Wang(王维华) Chin. Phys. B, 2021, 30 (5):  057304.  DOI: 10.1088/1674-1056/abdb1a Abstract ( 869 )   HTML ( 22 )   PDF (910KB) ( 611 )   Low dimensional materials are suitable candidates applying in next-generation high-performance electronic, optoelectronic, and energy storage devices because of their uniquely physical and chemical properties. In particular, one-dimensional (1D) atomic wires (AWs) exfoliating from 1D van der Waals (vdW) bulks are more promising in next generation nanometer (nm) even sub-nm device applications owing to their width of few-atoms scale and free dandling bonds states. Although several 1D AWs have been experimentally prepared, few 1D AW candidates could be practically applied in devices owing to lack of enough suitable 1D AWs. Herein, 367 kinds of 1D AWs have been screened and the corresponding computational database including structures, electronic structures, magnetic states, and stabilities of these 1D AWs has been organized and established. Among these systems, unary and binary 1D AWs with relatively small exfoliation energy are thermodynamically stable and theoretically feasible to be exfoliated. More significantly, rich quantum states emerge, such as 1D semiconductors, 1D metals, 1D semimetals, and 1D magnetism. This database will offer an ideal platform to further explore exotic quantum states and exploit practical device applications using 1D materials. The database are openly available at http://www.dx.doi.org/10.11922/sciencedb.j00113.00004.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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Absence of magnetic order in dichloro [1,2-bis (diphenylphosphino) ethane] nickel2 + single crystal Shuaiqi Ma(马帅奇), Linlin An(安琳琳), and Xiangde Zhu(朱相德) Chin. Phys. B, 2021, 30 (5):  057501.  DOI: 10.1088/1674-1056/abe233 Abstract ( 497 )   HTML ( 1 )   PDF (906KB) ( 150 )   Dichloro [1,2-bis (diphenylphosphino) ethane] nickel2+ (NiCl2(dppe)) is an organic compound containing C26H24P2(dppe) molecules and Cl-, Ni2+ ions. The large-size NiCl2(dppe) single crystals with longest dimension of 4 mm were grown by the method of slow evaporation of organic solution. Single crystal x-ray diffraction spectrum indicates that the single crystal is of high quality. Magnetization results of the NiCl2(dppe) single crystals show an anisotropic paramagnetism behavior and diamagnetic background, which come from Ni2+ ions and benzene ring, respectively. However, according to the specific heat results with temperature down to 0.1 K and magnetic field up to 14 T, no expected field-induced quantum phase transition was observed in NiCl2(dppe) single crystals.

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Process modeling gas atomization of close-coupled ring-hole nozzle for 316L stainless steel powder production Peng Wang(汪鹏), Jing Li(李静), Hen-San Liu(刘恒三), Xin Wang(王欣), Bo-Rui Du(杜博睿), Ping Gan(甘萍), Shi-Yuan Shen(申世远), Bin Fan(范斌), Xue-Yuan Ge(葛学元), and Miao-Hui Wang(王淼辉) Chin. Phys. B, 2021, 30 (5):  057502.  DOI: 10.1088/1674-1056/abd771 Abstract ( 533 )   HTML ( 1 )   PDF (7874KB) ( 227 )   The paper aims at modeling and simulating the atomization process of the close-coupled ring-hole nozzle in vacuum induction gas atomization (VIGA) for metallic powder production. First of all, the primary atomization of the ring-hole nozzle is simulated by the volume of fluid (VOF) coupled large eddy simulation (LES) model. To simulate the secondary atomization process, we use the method of selecting the droplet sub-model and the VOF model. The results show that the ring-hole nozzle forms a gas recirculation zone at the bottom of the delivery tube, which is the main reason for the formation of an annular liquid film during the primary atomization. In addition, the primary atomization process of the ring-hole nozzle consists of three stages: the formation of the serrated liquid film tip, the appearance and shedding of the ligaments, and the fragmentation of ligaments. At the same time, the primary atomization mainly forms spherical droplets and long droplets, but only the long droplets can be reserved and proceed to the secondary atomization. Moreover, increasing the number of ring holes from 18 to 30, the mass median diameter (MMD, d50) of the primary atomized droplets decreases first and then increases, which is mainly due to the change of the thickness of the melt film. Moreover, the secondary atomization of the ring-hole nozzles is mainly in bag breakup mode and multimode breakup model, and bag breakup will result in the formation of hollow powder, which can be avoided by increasing the gas velocity.

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Magnetization and magnetic phase diagrams of a spin-1/2 ferrimagnetic diamond chain at low temperature Tai-Min Cheng(成泰民), Mei-Lin Li(李美霖), Zhi-Rui Cheng(成智睿), Guo-Liang Yu(禹国梁), Shu-Sheng Sun(孙树生), Chong-Yuan Ge(葛崇员), and Xin-Xin Zhang(张新欣) Chin. Phys. B, 2021, 30 (5):  057503.  DOI: 10.1088/1674-1056/abd768 Abstract ( 504 )   HTML ( 1 )   PDF (954KB) ( 61 )   We used the Jordan-Wigner transform and the invariant eigenoperator method to study the magnetic phase diagram and the magnetization curve of the spin-1/2 alternating ferrimagnetic diamond chain in an external magnetic field at finite temperature. The magnetization versus external magnetic field curve exhibits a 1/3 magnetization plateau at absolute zero and finite temperatures, and the width of the 1/3 magnetization plateau was modulated by tuning the temperature and the exchange interactions. Three critical magnetic field intensities $H_{\rm CB}$, $H_{\rm CE}$ and $H_{\rm CS}$ were obtained, in which the $H_{\rm CB}$ and $H_{\rm CE}$ correspond to the appearance and disappearance of the 1/3 magnetization plateau, respectively, and the higher $H_{\rm CS}$ correspond to the appearance of fully polarized magnetization plateau of the system. The energies of elementary excitation ${\hslash \omega }_{\sigma,k}\,\,{(\sigma =1, 2, 3)}$ present the extrema of zero at the three critical magnetic fields at 0 K, i.e., $\left[ {{\hslash }\omega }_{{3,}k}\left(H_{\rm {CB}} \right) \right]_{{\min}}{=0}$, $\left[ \hslash \omega _{{2,}k}\left(H_{\rm{CE}} \right) \right]_{{\max}}{=0}$ and $\left[ {{\hslash }\omega }_{{2,k}}\left(H_{\rm{CS}} \right) \right]_{{\min}}{=0}$, and the magnetic phase diagram of magnetic field versus different exchange interactions at 0 K was established by the above relationships. According to the relationships between the system's magnetization curve at finite temperatures and the critical magnetic field intensities, the magnetic field-temperature phase diagram was drawn. It was observed that if the magnetic phase diagram shows a three-phase critical point, which is intersected by the ferrimagnetic phase, the ferrimagnetic plateau phase, and the Luttinger liquid phase, the disappearance of the 1/3 magnetization plateau would inevitably occur. However, the 1/3 magnetization plateau would not disappear without the three-phase critical point. The appearance of the 1/3 magnetization plateau in the low temperature region is the macroscopic manifestations of quantum effect.

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Electric-field-induced in-plane effective 90° magnetization rotation in Co2FeAl/PMN-PT structure Cai Zhou(周偲), Dengyu Zhu(朱登玉), Fufu Liu(刘福福), Cunfang Feng(冯存芳), Mingfang Zhang(张铭芳), Lei Ding(丁磊), Mingyao Xu(许明耀), and Shengxiang Wang(汪胜祥) Chin. Phys. B, 2021, 30 (5):  057504.  DOI: 10.1088/1674-1056/abd7de Abstract ( 462 )   HTML ( 1 )   PDF (813KB) ( 85 )   The in-plane effective 90° magnetization rotation of Co2FeAl thin film grown on PMN-PT substrate induced by the electric field is investigated at room temperature. The magnetic hysteresis loops under different positive and negative electric fields are obtained, which reveals remanent magnetization can be mediated by the electric field. Moreover, under positive electric fields, the obvious 90° magnetization rotation can be observed, while remanent magnetization is nearly unchanged under negative electric fields. The result is consistent with the electric field dependence of effective magnetic field, which can be attributed to the piezostrain effect in Co2FeAl/PMN-PT structure. In addition, the piezostrain-mediated 90° magnetization rotation can be demonstrated by the result of resonance field changing with electric field in the measurement of ferromagnetic resonance, which is promising for the design of future multiferroic devices.

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Effect of hydrogen plasma implantation on the micro-structure and magnetic properties of hcp-Co8057Fe4Ir16 thin films Hui Wang(王辉), Meng Wu(吴猛), Haiping Zhou(周海平), Bo Zhang(张博), Shixin Hu(胡世欣), Tianyong Ma(马天勇), Zhiwei Li(李志伟), Liang Qiao(乔亮), Tao Wang(王涛), and Fashen Li(李发伸) Chin. Phys. B, 2021, 30 (5):  057505.  DOI: 10.1088/1674-1056/abe0c3 Abstract ( 654 )   HTML ( 2 )   PDF (4310KB) ( 164 )   We present detailed investigations of structural and static/dynamic magnetic properties of hydrogenated hcp-Co8057Fe4Ir16 soft magnetic thin films. Two different kinds of defects, i.e., destructive and non-destructive, were demonstrated by controlling the negative bias voltage of the hydrogenation process. Our results show that the structure and magnetic properties of our sample can be tuned by the density of the induced defects. These results provide better understanding of the hydrogenation effect and thus can be used in the future for materials processing to meet the requirements of different devices.

RAPID COMMUNICATION

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Thermally induced band hybridization in bilayer-bilayer MoS2/WS2 heterostructure Hot! Yanchong Zhao(赵岩翀), Tao Bo(薄涛), Luojun Du(杜罗军), Jinpeng Tian(田金朋), Xiaomei Li(李晓梅), Kenji Watanabe, Takashi Taniguchi, Rong Yang(杨蓉), Dongxia Shi(时东霞), Sheng Meng(孟胜), Wei Yang(杨威), and Guangyu Zhang(张广宇) Chin. Phys. B, 2021, 30 (5):  057801.  DOI: 10.1088/1674-1056/abeee3 Abstract ( 939 )   HTML ( 2 )   PDF (4994KB) ( 543 )   Transition metal dichalcogenides (TMDs), being valley selectively, are an ideal system hosting excitons. Stacking TMDs together to form heterostructure offers an exciting platform to engineer new optical and electronic properties in solid-state systems. However, due to the limited accuracy and repetitiveness of sample preparation, the effects of interlayer coupling on the electronic and excitonic properties have not been systematically investigated. In this report, we study the photoluminescence spectra of bilayer-bilayer MoS2/WS2 heterostructure with a type Ⅱ band alignment. We demonstrate that thermal annealing can increase interlayer coupling in the van der Waals heterostructures, and after thermally induced band hybridization such heterostructure behaves more like an artificial new solid, rather than just the combination of two individual TMD components. We also carry out experimental and theoretical studies of the electric controllable direct and indirect infrared interlayer excitons in such system. Our study reveals the impact of interlayer coupling on interlayer excitons and will shed light on the understanding and engineering of layer-controlled spin-valley configuration in twisted van der Waals heterostructures.

CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

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High-efficiency reflection phase tunable metasurface at near-infrared frequencies Ce Li(李策), Wei Zhu(朱维), Shuo Du(杜硕), Junjie Li(李俊杰), and Changzhi Gu(顾长志) Chin. Phys. B, 2021, 30 (5):  057802.  DOI: 10.1088/1674-1056/abe9a6 Abstract ( 433 )   HTML ( 3 )   PDF (1635KB) ( 199 )   The realization of active modulation of reflection phase based on metasurfaces is of great significance for flexible control of electromagnetic wavefront, which makes metasurfaces have practical application values in polarization conversion, beam steering, metalens, etc. In this paper, a reflection phase tunable gap-surface plasmon (GSP) metasurface based on phase change materials Ge2Sb2Te5 (GST) is designed and experimentally demonstrated. By virtue of the characteristics of large permittivities difference before and after GST phase transition and the existence of stable intermediate states, the continuous modulation of near-infrared reflection phase larger than 200° has been realized. At the same time, through the reasonable design of the structure sizes, the reflection has been maintained at about 0.4 and basically does not change with the GST phase transition, which improved the working efficiency of the metasurface significantly. In addition, the coupled-mode theory (CMT) is introduced to make a full analysis of the modulation mechanism of the reflection phase, which proves that the phase transition of GST can induce the transition of metasurface working state from overcoupling mode to critical coupling mode. The improvement of the metasurface working efficiency has practical values for wavefront modulation.

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Localized electric-field-enhanced low-light detection by a 2D SnS visible-light photodetector Hao Wen(文豪), Li Xiong(熊力), Congbing Tan(谭丛兵), Kaimin Zhu(朱凯民), Yong Tang(唐勇), Jinbin Wang(王金斌), and Xiangli Zhong(钟向丽) Chin. Phys. B, 2021, 30 (5):  057803.  DOI: 10.1088/1674-1056/abd7db Abstract ( 376 )   HTML ( 2 )   PDF (1014KB) ( 77 )   Due to their excellent carrier mobility, high absorption coefficient and narrow bandgap, most 2D IVA metal chalcogenide semiconductors (GIVMCs, metal = Ge, Sn, Pb；chalcogen = S, Se) are regarded as promising candidates for realizing high-performance photodetectors. We synthesized high-quality two-dimensional (2D) tin sulfide (SnS) nanosheets using the physical vapor deposition (PVD) method and fabricated a 2D SnS visible-light photodetector. The photodetector exhibits a high photoresponsivity of 161 A·W-1 and possesses an external quantum efficiency of 4.45×104%, as well as a detectivity of 1.15×109 Jones under 450 nm blue light illumination. Moreover, under poor illumination at optical densities down to 2 mW·cm-2, the responsivity of the device is higher than that at stronger optical densities. We suggest that a photogating effect in the 2D SnS photodetector is mainly responsible for its low-light responsivity. Defects and impurities in 2D SnS can trap carriers and form localized electric fields, which can delay the recombination process of electron-hole pairs, prolong carrier lifetimes, and thus improve the low-light responsivity. This work provides design strategies for detecting low levels of light using photodetectors made of 2D materials.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Enhanced interface properties of diamond MOSFETs with Al2O3 gate dielectric deposited via ALD at a high temperature Yu Fu(付裕), Rui-Min Xu(徐锐敏), Xin-Xin Yu(郁鑫鑫), Jian-Jun Zhou(周建军), Yue-Chan Kong(孔月婵), Tang-Sheng Chen(陈堂胜), Bo Yan(延波), Yan-Rong Li(李言荣), Zheng-Qiang Ma(马正强), and Yue-Hang Xu(徐跃杭) Chin. Phys. B, 2021, 30 (5):  058101.  DOI: 10.1088/1674-1056/abd749 Abstract ( 669 )   HTML ( 2 )   PDF (1096KB) ( 144 )   The interface state of hydrogen-terminated (C-H) diamond metal-oxide-semiconductor field-effect transistor (MOSFET) is critical for device performance. In this paper, we investigate the fixed charges and interface trap states in C-H diamond MOSFETs by using different gate dielectric processes. The devices use Al$_{2}$O$_{3}$ as gate dielectrics that are deposited via atomic layer deposition (ALD) at 80 $^\circ$C and 300 $^\circ$C, respectively, and their $C$-$V$ and $I$-$V$ characteristics are comparatively investigated. Mott-Schottky plots ($1/C^{2}$-$V_{\rm G}$) suggest that positive and negative fixed charges with low density of about 10$^{11}$ cm$^{-2}$ are located in the 80-$^\circ$C- and 300-$^\circ$C deposition Al$_{2}$O$_{3}$ films, respectively. The analyses of direct current (DC)/pulsed $I$-$V$ and frequency-dependent conductance show that the shallow interface traps (0.46 eV-0.52 eV and 0.53 eV-0.56 eV above the valence band of diamond for the 80-$^\circ$C and 300-$^\circ$C deposition conditions, respectively) with distinct density ($7.8 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$-$8.5 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$ and $2.2 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$-$5.1 \times 10^{13}$ eV$^{-1}\cdot$cm$^{-2}$ for the 80-$^\circ$C- and 300-$^\circ$C-deposition conditions, respectively) are present at the Al$_{2}$O$_{3}$/C-H diamond interface. Dynamic pulsed $I$-$V$ and capacitance dispersion results indicate that the ALD Al$_{2}$O$_{3}$ technique with 300-$^\circ$C deposition temperature has higher stability for C-H diamond MOSFETs.

SPECIAL TOPIC—Physics in neuromorphic devices

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Synaptic plasticity and classical conditioning mimicked in single indium-tungsten-oxide based neuromorphic transistor Rui Liu(刘锐), Yongli He(何勇礼), Shanshan Jiang(姜珊珊), Li Zhu(朱力), Chunsheng Chen(陈春生), Ying Zhu(祝影), and Qing Wan(万青) Chin. Phys. B, 2021, 30 (5):  058102.  DOI: 10.1088/1674-1056/abc163 Abstract ( 554 )   HTML ( 3 )   PDF (900KB) ( 319 )   Emulation of synaptic function by ionic/electronic hybrid device is crucial for brain-like computing and neuromorphic systems. Electric-double-layer (EDL) transistors with proton conducting electrolytes as the gate dielectrics provide a prospective approach for such application. Here, artificial synapses based on indium-tungsten-oxide (IWO)-based EDL transistors are proposed, and some important synaptic functions (excitatory post-synaptic current, paired-pulse facilitation, filtering) are emulated. Two types of spike-timing-dependent plasticity (Hebbian STDP and anti-Hebbian STDP) learning rules and multistore memory (sensory memory, short-term memory, and long-term memory) are also mimicked. At last, classical conditioning is successfully demonstrated. Our results indicate that IWO-based neuromorphic transistors are interesting for neuromorphic applications.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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High efficiency and broad bandwidth terahertz vortex beam generation based on ultra-thin transmission Pancharatnam-Berry metasurfaces Wenyu Li(李文宇), Guozhong Zhao(赵国忠), Tianhua Meng(孟田华), Ran Sun(孙然), and Jiaoyan Guo(郭姣艳) Chin. Phys. B, 2021, 30 (5):  058103.  DOI: 10.1088/1674-1056/abd75c Abstract ( 630 )   HTML ( 5 )   PDF (1120KB) ( 145 )   The terahertz (THz) vortex beam generators are designed and theoretically investigated based on single-layer ultra-thin transmission metasurfaces. Noncontinuous phase changes of metasurfaces are obtained by utilizing Pancharatnam-Berry phase elements, which possess different rotation angles and are arranged on two concentric rings centered on the origin. The circularly polarized incident THz beam could be turned into a cross-polarization transmission wave, and the orbital angular momentum (OAM) varies in value by $l\hbar$. The $l$ values change from $\pm 1$ to $\pm 5$, and the maximal cross-polarization conversion efficiency that could be achieved is 23%, which nearly reaches the theoretical limit of a single-layer structure. The frequency range of the designed vortex generator is from 1.2 THz to 1.9 THz, and the generated THz vortex beam could keep a high fidelity in the operating bandwidth. The propagation behavior of the emerged THz vortex beam is analyzed in detail. Our work offers a novel way of designing ultra-thin and single-layer vortex beam generators, which have low process complexity, high conversion efficiency and broad bandwidth.

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Dynamics analysis in a tumor-immune system with chemotherapy Hai-Ying Liu(刘海英), Hong-Li Yang(杨红丽), and Lian-Gui Yang(杨联贵) Chin. Phys. B, 2021, 30 (5):  058201.  DOI: 10.1088/1674-1056/abcf49 Abstract ( 611 )   HTML ( 4 )   PDF (1902KB) ( 97 )   An ordinary differential equation (ODE) model of tumor growth with the effect of tumor-immune interaction and chemotherapeutic drug is presented and studied. By analyzing the existence and stability of equilibrium points, the dynamic behavior of the system is discussed elaborately. The chaotic dynamics can be obtained in our model by equilibria analysis, which show the existence of chaos by calculating the Lyapunov exponents and the Lyapunov dimension of the system. Moreover, the action of the infusion rate of the chemotherapeutic drug on the resulting dynamics is investigated, which suggests that the application of chemotherapeutic drug can effectively control tumor growth. However, in the case of high-dose chemotherapeutic drug, chemotherapy-induced effector immune cells damage seriously, which may cause treatment failure.

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Unpinning the spiral waves by using parameter waves Lu Peng(彭璐) and Jun Tang(唐军) Chin. Phys. B, 2021, 30 (5):  058202.  DOI: 10.1088/1674-1056/abd46e Abstract ( 491 )   HTML ( 1 )   PDF (971KB) ( 82 )   The spiral waves anchored to heterogeneous areas are more difficult to control and eliminate than freely rotating ones in homogenous mediums. To eliminate pinned spiral waves, the resistant force should be provided to resist the pinning force. Other than advection field, we introduce parametric wave to play the role of providing resistant force. It is found that the parametric wave with large enough amplitude and proper frequency can unpin and eliminate the spiral wave successfully. The capability of parametric wave in providing resistant force is dependent on its amplitude and frequency sensitively. On the basis of parametric wave, the dependence of pinning force on the size and level of heterogeneity is further confirmed.

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Vertical polarization-induced doping InN/InGaN heterojunction tunnel FET with hetero T-shaped gate Yuan-Hao He(何元浩), Wei Mao(毛维), Ming Du(杜鸣), Zi-Ling Peng(彭紫玲), Hai-Yong Wang(王海永), Xue-Feng Zheng(郑雪峰), Chong Wang(王冲), Jin-Cheng Zhang(张进成), and Yue Hao(郝跃) Chin. Phys. B, 2021, 30 (5):  058501.  DOI: 10.1088/1674-1056/abd73f Abstract ( 482 )   HTML ( 1 )   PDF (1014KB) ( 115 )   A novel vertical InN/InGaN heterojunction tunnel FET with hetero T-shaped gate as well as polarization-doped source and drain region (InN-Hetero-TG-TFET) is proposed and investigated by Silvaco-Atlas simulations for the first time. Compared with the conventional physical doping TFET devices, the proposed device can realize the P-type source and N-type drain region by means of the polarization effect near the top InN/InGaN and bottom InGaN/InN heterojunctions respectively, which could provide an effective solution of random dopant fluctuation (RDF) and the related problems about the high thermal budget and expensive annealing techniques due to ion-implantation physical doping. Besides, due to the hetero T-shaped gate, the improvement of the on-state performance can be achieved in the proposed device. The simulations of the device proposed here in this work show ION of 4.45×10-5 A/μm, ION/IOFF ratio of 1013, and SSavg of 7.5 mV/dec in InN-Hetero-TG-TFET, which are better than the counterparts of the device with a homo T-shaped gate (InN-Homo-TG-TFET) and our reported lateral polarization-induced InN-based TFET (PI-InN-TFET). These results can provide useful reference for further developing the TFETs without physical doping process in low power electronics applications.

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Improved 4H-SiC UMOSFET with super-junction shield region Pei Shen(沈培), Ying Wang(王颖), Xing-Ji Li(李兴冀), Jian-Qun Yang(杨剑群), Cheng-Hao Yu(于成浩), and Fei Cao(曹菲) Chin. Phys. B, 2021, 30 (5):  058502.  DOI: 10.1088/1674-1056/abd740 Abstract ( 679 )   HTML ( 5 )   PDF (1030KB) ( 238 )   This article investigates an improved 4H-SiC trench gate metal-oxide-semiconductor field-effect transistor (MOSFET) (UMOSFET) fitted with a super-junction (SJ) shielded region. The modified structure is composed of two n-type conductive pillars, three p-type conductive pillars, an oxide trench under the gate, and a light n-type current spreading layer (NCSL) under the p-body. The n-type conductive pillars and the light n-type current spreading layer provide two paths to and promote the diffusion of a transverse current in the epitaxial layer, thus improving the specific on-resistance ($R_{\rm on,sp}$). There are three p-type pillars in the modified structure, with the p-type pillars on both sides playing the same role. The p-type conductive pillars relieve the electric field ($E$-field) in the corner of the trench bottom. Two-dimensional simulation (silvaco TCAD) indicates that $R_{\rm on,sp }$ of the modified structure, and breakdown voltage ($V_{\rm BR}$) are improved by 22.2% and 21.1% respectively, while the maximum figure of merit (${\rm FOM}=V^{2}_{\rm BR}/R_{\rm on,sp}$) is improved by 79.0%. Furthermore, the improved structure achieves a light smaller low gate-to-drain charge ($Q_{\rm gd}$) and when compared with the conventional UMOSFET (conventional-UMOS), it displays great advantages for reducing the switching energy loss. These advantages are due to the fact that the p-type conductive pillars and n-type conductive pillars configured under the gate provide a substantial charge balance, which also enables the charge carriers to be extracted quickly. In the end, under the condition of the same total charge quantity, the simulation comparison of gate charge and OFF-state characteristics between Gauss-doped structure and uniform-doped structure shows that Gauss-doped structure increases the $V_{\rm BR}$ of the device without degradation of dynamic performance.

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Design of sextuple-mode triple-ring HTS UWB filter using two-round interpolation Ming-En Tian(田明恩), Zhi-He Long(龙之河), You Lan(蓝友), Lei-Lei He(贺磊磊), and Tian-Liang Zhang(张天良) Chin. Phys. B, 2021, 30 (5):  058503.  DOI: 10.1088/1674-1056/abd7e1 Abstract ( 562 )   HTML ( 1 )   PDF (603KB) ( 89 )   A single-stage ring resonator capable of introducing six modes within the ultra-wideband (UWB) passband is presented. The sextuple-mode resonator consists of three rings and three sets of stepped-impedance open stubs. Based on this sextuple-mode resonator, a UWB filter fed by the interdigital-coupling line (ICL) is designed. And we propose a two-round interpolation method to obtain the filter's initial dimensions. The designed filter is fabricated on a double-sided YBCO/MgO/YBCO high-temperature superconducting (HTS) thin film for demonstration. The experimental results show that this UWB filter produces eight resonances in the passband eventually, which effectively improves the in-band reflection and the band-edge steepness. Moreover, the upper stopband performance is enhanced due to the transmission zeros (TZs) generated by the stepped-impedance open stubs and the ICL structure. The measured good performance verifies the practicability of the two-round interpolation approach, which can also be extended to other odd-even-mode filter designs.

REVIEW

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Universal memory based on phase-change materials: From phase-change random access memory to optoelectronic hybrid storage Bo Liu(刘波), Tao Wei(魏涛), Jing Hu(胡敬), Wanfei Li(李宛飞), Yun Ling(凌云), Qianqian Liu(刘倩倩), Miao Cheng(程淼), and Zhitang Song(宋志棠) Chin. Phys. B, 2021, 30 (5):  058504.  DOI: 10.1088/1674-1056/abeedf Abstract ( 434 )   HTML ( 2 )   PDF (3026KB) ( 295 )   The era of information explosion is coming and information need to be continuously stored and randomly accessed over long-term periods, which constitute an insurmountable challenge for existing data centers. At present, computing devices use the von Neumann architecture with separate computing and memory units, which exposes the shortcomings of “memory bottleneck”. Nonvolatile memristor can realize data storage and in-memory computing at the same time and promises to overcome this bottleneck. Phase-change random access memory (PCRAM) is called one of the best solutions for next generation non-volatile memory. Due to its high speed, good data retention, high density, low power consumption, PCRAM has the broad commercial prospects in the in-memory computing application. In this review, the research progress of phase-change materials and device structures for PCRAM, as well as the most critical performances for a universal memory, such as speed, capacity, and power consumption, are reviewed. By comparing the advantages and disadvantages of phase-change optical disk and PCRAM, a new concept of optoelectronic hybrid storage based on phase-change material is proposed. Furthermore, its feasibility to replace existing memory technologies as a universal memory is also discussed as well.

SPECIAL TOPIC—Ion beam modification of materials and applications

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Cathodic shift of onset potential on TiO2 nanorod arrays with significantly enhanced visible light photoactivity via nitrogen/cobalt co-implantation Xianyin Song(宋先印), Hongtao Zhou(周洪涛), and Changzhong Jiang(蒋昌忠) Chin. Phys. B, 2021, 30 (5):  058505.  DOI: 10.1088/1674-1056/abee07 Abstract ( 578 )   HTML ( 1 )   PDF (1195KB) ( 131 )   Despite anionic doping has been widely implemented to increase the visible light activity of TiO$_{2}$, it often gives rise to a dramatical anodic shift in current onset potential. Herein, we show an effective method to achieve the huge cathodic shift of TiO$_{2}$ photoanode with significantly enhanced visible light photo-electrochemical activity by nitrogen/cobalt co-implantation. The nitrogen/cobalt co-doped TiO$_{2}$ nanorod arrays (N/Co-TiO$_{2}$) exhibit a cathodic shift of 350 mV in onset potential relative to only nitrogen-doped TiO$_{2}$ (N-TiO$_{2}$). Moreover, the visible-light ($\lambda >420 $ nm) photocurrent density of N/Co-TiO$_{2}$ reaches 0.46 mA/cm$^{2}$, far exceeding 0.07 mA/cm$^{2}$ in N-TiO$_{2}$ at 1.23 V $versus$ reversible hydrogen electrode (RHE). Systematic characterization studies demonstrate that the enhanced photo-electrochemical performance can be attributed to the surface synergic sputtering of high-energy nitrogen/cobalt ions.

RAPID COMMUNICATION

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Enhancements of the Gaussian network model in describing nucleotide residue fluctuations for RNA Hot! Wen-Jing Wang(王文静) and Ji-Guo Su(苏计国) Chin. Phys. B, 2021, 30 (5):  058701.  DOI: 10.1088/1674-1056/abe1a5 Abstract ( 596 )   HTML ( 1 )   PDF (768KB) ( 227 )   Gaussian network model (GNM) is an efficient method to investigate the structural dynamics of biomolecules. However, the application of GNM on RNAs is not as good as that on proteins, and there is still room to improve the model. In this study, two novel approaches, named the weighted GNM (wGNM) and the force-constant-decayed GNM (fcdGNM), were proposed to enhance the performance of ENM in investigating the structural dynamics of RNAs. In wGNM, the force constant for each spring is weighted by the number of interacting heavy atom pairs between two nucleotides. In fcdGNM, all the pairwise nucleotides were connected by springs and the force constant decayed exponentially with the separate distance of the nucleotide pairs. The performance of these two proposed models was evaluated by using a non-redundant RNA structure database composed of 51 RNA molecules. The calculation results show that both the proposed models outperform the conventional GNM in reproducing the experimental B-factors of RNA structures. Compared with the conventional GNM, the Pearson correlation coefficient between the predicted and experimental B-factors was improved by 9.85% and 6.76% for wGNM and fcdGNM, respectively. Our studies provide two candidate methods for better revealing the dynamical properties encoded in RNA structures.

TOPICAL REVIEW—Physics in neuromorphic devices

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Resistive switching memory for high density storage and computing Xiao-Xin Xu(许晓欣), Qing Luo(罗庆), Tian-Cheng Gong(龚天成), Hang-Bing Lv(吕杭炳), Qi Liu(刘琦), and Ming Liu(刘明) Chin. Phys. B, 2021, 30 (5):  058702.  DOI: 10.1088/1674-1056/abe0c4 Abstract ( 711 )   HTML ( 3 )   PDF (12767KB) ( 718 )   The resistive random access memory (RRAM) has stimulated a variety of promising applications including programmable analog circuit, massive data storage, neuromorphic computing, etc. These new emerging applications have huge demands on high integration density and low power consumption. The cross-point configuration or passive array, which offers the smallest footprint of cell size and feasible capability of multi-layer stacking, has received broad attention from the research community. In such array, correct operation of reading and writing on a cell relies on effective elimination of the sneaking current coming from the neighboring cells. This target requires nonlinear I-V characteristics of the memory cell, which can be realized by either adding separate selector or developing implicit build-in nonlinear cells. The performance of a passive array largely depends on the cell nonlinearity, reliability, on/off ratio, line resistance, thermal coupling, etc. This article provides a comprehensive review on the progress achieved concerning 3D RRAM integration. First, the authors start with a brief overview of the associative problems in passive array and the category of 3D architectures. Next, the state of the arts on the development of various selector devices and self-selective cells are presented. Key parameters that influence the device nonlinearity and current density are outlined according to the corresponding working principles. Then, the reliability issues in 3D array are summarized in terms of uniformity, endurance, retention, and disturbance. Subsequently, scaling issue and thermal crosstalk in 3D memory array are thoroughly discussed, and applications of 3D RRAM beyond storage, such as neuromorphic computing and CMOL circuit are discussed later. Summary and outlooks are given in the final.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Contagion dynamics on adaptive multiplex networks with awareness-dependent rewiring Xiao-Long Peng(彭小龙) and Yi-Dan Zhang(张译丹) Chin. Phys. B, 2021, 30 (5):  058901.  DOI: 10.1088/1674-1056/abe1ab Abstract ( 525 )   HTML ( 4 )   PDF (4592KB) ( 329 )   Over the last few years, the interplay between contagion dynamics of social influences (e.g., human awareness, risk perception, and information dissemination) and biological infections has been extensively investigated within the framework of multiplex networks. The vast majority of existing multiplex network spreading models typically resort to heterogeneous mean-field approximation and microscopic Markov chain approaches. Such approaches usually manifest richer dynamical properties on multiplex networks than those on simplex networks; however, they fall short of a subtle analysis of the variations in connections between nodes of the network and fail to account for the adaptive behavioral changes among individuals in response to epidemic outbreaks. To transcend these limitations, in this paper we develop a highly integrated effective degree approach to modeling epidemic and awareness spreading processes on multiplex networks coupled with awareness-dependent adaptive rewiring. This approach keeps track of the number of nearest neighbors in each state of an individual; consequently, it allows for the integration of changes in local contacts into the multiplex network model. We derive a formula for the threshold condition of contagion outbreak. Also, we provide a lower bound for the threshold parameter to indicate the effect of adaptive rewiring. The threshold analysis is confirmed by extensive simulations. Our results show that awareness-dependent link rewiring plays an important role in enhancing the transmission threshold as well as lowering the epidemic prevalence. Moreover, it is revealed that intensified awareness diffusion in conjunction with enhanced link rewiring makes a greater contribution to disease prevention and control. In addition, the critical phenomenon is observed in the dependence of the epidemic threshold on the awareness diffusion rate, supporting the metacritical point previously reported in literature. This work may shed light on understanding of the interplay between epidemic dynamics and social contagion on adaptive networks.