Table of contents

05 January 2019, Volume 28 Issue 1 Previous issue    Next issue

GENERAL

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A nonlocal Burgers equation in atmospheric dynamical system and its exact solutions Xi-Zhong Liu(刘希忠), Jun Yu(俞军), Zhi-Mei Lou(楼智美), Xian-Min Qian(钱贤民) Chin. Phys. B, 2019, 28 (1):  010201.  DOI: 10.1088/1674-1056/28/1/010201 Abstract ( 859 )   HTML   PDF (1200KB) ( 201 )   From a two-vortex interaction model in atmospheric and oceanic systems, a nonlocal counterpart with shifted parity and delayed time reversal is derived by a simple AB reduction. To obtain some approximate analytic solutions of this nonlocal system, the multi-scale expansion method is applied to get an AB-Burgers system. Various exact solutions of the AB-Burgers equation, including elliptic periodic waves, kink waves and solitary waves, are obtained and shown graphically. To show the applications of these solutions in describing correlated events, a simple approximate solution for the two-vortex interaction model is given to show two correlated dipole blocking events at two different places. Furthermore, symmetry reduction solutions of the nonlocal AB-Burgers equation are also given by using the standard Lie symmetry method.

COMMENT

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A note on “Lattice soliton equation hierarchy and associated properties” Xi-Xiang Xu(徐西祥), Min Guo(郭敏) Chin. Phys. B, 2019, 28 (1):  010202.  DOI: 10.1088/1674-1056/28/1/010202 Abstract ( 644 )   HTML   PDF (343KB) ( 147 )   We demonstrate that the new hierarchy of integrable lattice equations in Chin. Phys. B 21 090202 (2012) can be changed into the integrable lattice hierarchy in Chin. Phys. B 13 1009 (2004) by using a very simple transformation.

GENERAL

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Stationary response of stochastic viscoelastic system with the right unilateral nonzero offset barrier impacts Deli Wang(王德莉), Wei Xu(徐伟), Xudong Gu(谷旭东) Chin. Phys. B, 2019, 28 (1):  010203.  DOI: 10.1088/1674-1056/28/1/010203 Abstract ( 617 )   HTML   PDF (7449KB) ( 147 )   The stationary response of viscoelastic dynamical system with the right unilateral nonzero offset barrier impacts subjected to stochastic excitations is investigated. First, the viscoelastic force is approximately treated as equivalent terms associated with effects. Then, the free vibro-impact (VI) system is absorbed to describe the periodic motion without impacts and quasi-periodic motion with impacts based upon the level of system energy. The stochastic averaging of energy envelope (SAEE) is adopted to seek the stationary probability density functions (PDFs). The detailed theoretical results for Van der Pol viscoelastic VI system with the right unilateral nonzero offset barrier are solved to demonstrate the important effects of the viscoelastic damping and nonzero rigid barrier impacts condition. Monte Carlo (MC) simulation is also performed to verify the reliability of the suggested approach. The stochastic P-bifurcation caused by certain system parameters is further explored. The variation of elastic modulus from negative to zero and then to positive witnesses the evolution process of stochastic P-bifurcation. From the vicinity of the common value to a wider range, the relaxation time induces the stochastic P-bifurcation in the two interval schemes.

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Direct measurement of the concurrence of hybrid entangled state based on parity check measurements Man Zhang(张曼), Lan Zhou(周澜), Wei Zhong(钟伟), Yu-Bo Sheng(盛宇波) Chin. Phys. B, 2019, 28 (1):  010301.  DOI: 10.1088/1674-1056/28/1/010301 Abstract ( 698 )   HTML   PDF (382KB) ( 176 )   The hybrid entangled state is widely discussed in quantum information processing. In this paper, we propose the first protocol to directly measure the concurrence of the hybrid entangled state. To complete the measurement, we design parity check measurements (PCMs) for both the single polarization qubit and the coherent state. In this protocol, we perform three rounds of PCMs. The results show that we can convert the concurrence into the success probability of picking up the correct states from the initial entangled states. This protocol only uses polarization beam splitters, beam splitters, and weak cross-Kerr nonlinearities, which is feasible for future experiments. This protocol may be useful in future quantum information processing.

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Noiseless linear amplification for the single-photon entanglement of arbitrary polarization-time-bin qudit Ling-Quan Chen(陈灵泉), Yu-Bo Sheng(盛宇波), Lan Zhou(周澜) Chin. Phys. B, 2019, 28 (1):  010302.  DOI: 10.1088/1674-1056/28/1/010302 Abstract ( 571 )   HTML   PDF (429KB) ( 155 )   Single-photon entanglement (SPE) is an important source in quantum communication. In this paper, we put forward a single-photon-assisted noiseless linear amplification protocol to protect the SPE of an arbitrary polarization-time-bin qudit from the photon transmission loss caused by the practical channel noise. After the amplification, the fidelity of the SPE can be effectively increased. Meanwhile, the encoded polarization-time-bin features of the qudit can be well preserved. The protocol can be realized under the current experimental conditions. Moreover, the amplification protocol can be extended to resist complete photon loss and partial photon loss during the photon transmission. After the amplification, we can not only increase the fidelity of the target state, but also solve the decoherence problem simultaneously. Based on the above features, our amplification protocol may be useful in future quantum communication.

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Current-phase relations of a ring-trapped Bose-Einstein condensate with a weak link Xiu-Rong Zhang(张秀荣), Wei-Dong Li(李卫东) Chin. Phys. B, 2019, 28 (1):  010303.  DOI: 10.1088/1674-1056/28/1/010303 Abstract ( 566 )   HTML   PDF (623KB) ( 124 )   The current-phase relations of a ring-trapped Bose-Einstein condensate interrupted by a rotating rectangular barrier are extensively investigated with an analytical solution. A current-phase diagram, single and multi-valued relation, is presented with a rescaled barrier height and width. Our results show that the finite size makes the current-phase relation deviate a little bit from the cosine form for the soliton solution in the limit of a vanishing barrier, and the periodic boundary condition selects only the plane wave solution in the case of high barrier. The reason for multi-valued current-phase relation is given by investigating the behavior of soliton solution.

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Average fidelity estimation of twirled noisy quantum channel using unitary 2t-design Linxi Zhang(张林曦), Changhua Zhu(朱畅华), Changxing Pei(裴昌幸) Chin. Phys. B, 2019, 28 (1):  010304.  DOI: 10.1088/1674-1056/28/1/010304 Abstract ( 663 )   HTML   PDF (618KB) ( 169 )   We propose a method to estimate the average fidelity using the unitary 2t-design of a twirled noisy channel, which is suitable for large-scale quantum circuits. Compared with the unitary 2-design in randomized benchmarking, the unitary 2t-design for the twirling of noisy channels is more flexible in construction and can provide more information. In addition, we prove that the proposed method provides an efficient and reliable estimation of the average fidelity in benchmarking multistage quantum gates and estimating the weakly gate- and time-dependent noise. For time-dependent noise, we provide a scheme of moment superoperator to analyze the noise in different experiments. In particular, we give a lower bound on the average fidelity of a channel with imperfect implementation of benchmarking and state preparation and measurement errors (SPAM).

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Finite-size analysis of continuous-variable quantum key distribution with entanglement in the middle Ying Guo(郭迎), Yu Su(苏玉), Jian Zhou(周健), Ling Zhang(张玲), Duan Huang(黄端) Chin. Phys. B, 2019, 28 (1):  010305.  DOI: 10.1088/1674-1056/28/1/010305 Abstract ( 769 )   HTML   PDF (980KB) ( 203 )   Continuous-variable quantum key distribution (CVQKD) protocols with entanglement in the middle (EM) enable long maximal transmission distances for quantum communications. For the security analysis of the protocols, it is usually assumed that Eve performs collective Gaussian attacks and there is a lack of finite-size analysis of the protocols. However, in this paper we consider the finite-size regime of the EM-based CVQKD protocols by exposing the protocol to collective attacks and coherent attacks. We differentiate between the collective attacks and the coherent attacks while comparing asymptotic key rate and the key rate in the finite-size scenarios. Moreover, both symmetric and asymmetric configurations are collated in a contrastive analysis. As expected, the derived results in the finite-size scenarios are less useful than those acquired in the asymptotic regime. Nevertheless, we find that CVQKD with entanglement in the middle is capable of providing fully secure secret keys taking the finite-size effects into account with transmission distances of more than 30 km.

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Analytical treatment of Anderson localization in a chain of trapped ions experiencing laser Bessel beams Jun Wen(文军), Jian-Qi Zhang(张建奇), Lei-Lei Yan(闫磊磊), Mang Feng(冯芒) Chin. Phys. B, 2019, 28 (1):  010306.  DOI: 10.1088/1674-1056/28/1/010306 Abstract ( 865 )   HTML   PDF (1772KB) ( 145 )   Trapped ions, under electromagnetic confinement and Coulomb repulsion, can behave as non-interacting particles in one-dimensional lattices. Here we explore analytically the possible effects regarding Anderson localization in a chain of trapped ions experiencing laser Bessel beams. Under an experimentally feasible condition, we predict an analytical form of the energy-dependent mobility edges, which is verified to be in good agreement with the exact numerical results except for the top band. Some other important properties regarding the phonon localization in the ion chain are also discussed both analytically and numerically. Our results are relevant to experimental observation of localization-delocalization transition in the ion trap and helpful for deeper understanding of the rich phenomena due to long-range phonon hopping.

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Periodically modulated interaction effect on transport of Bose-Einstein condensates in lattice with local defects Kun-Qiang Zhu(朱坤强), Zi-Fa Yu(鱼自发), Ji-Ming Gao(高吉明), Ai-Xia Zhang(张爱霞), Hong-Ping Xu(徐红萍), Ju-Kui Xue(薛具奎) Chin. Phys. B, 2019, 28 (1):  010307.  DOI: 10.1088/1674-1056/28/1/010307 Abstract ( 632 )   HTML   PDF (477KB) ( 152 )   We theoretically investigate the periodically modulated interaction effect on the propagation properties of a traveling plane wave in a Bose-Einstein condensate (BEC) trapped in a deep annular lattice with local defects both analytically and numerically. By using the two-mode ansatz and the tight-binding approximation, a critical condition for the system preserving the superfluidity is obtained analytically and confirmed numerically. We find that the coupled effects of periodic modulated atomic interactions, the quasi-momentum of the plane wave, and the defect can control the superfluidity of the system. Particularly, when we consider the periodic modulation in the system with single defect, the critical condition for the system entering the superfluid regime depends on both the defect and the momentum of the plane wave. This is different from the case for the system without the periodic modulation, where the critical condition is only determined by the defect. The modulation and quasi-momentum of the plane wave can enhance the system entering the superfluid regime. Interestingly, when the modulated amplitude/frequency, the defect strength, and the quasi-momentum of the plane wave satisfy a certain condition, the system will always be in the superfluid region. This engineering provides a possible means for studying the periodic modulation effect on propagation properties and the corresponding dynamics of BECs in disordered optical lattices.

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Ground-state vortex structures of a rotating binary dipolar Bose-Einstein condensate confined in harmonic plus quartic potential Guang-Ping Chen(陈光平), Chang-Bing Qiao(乔昌兵), Hui Guo(郭慧), Lin-Xue Wang(王林雪), Ya-Jun Wang(王雅君), Ren-Bing Tan(谭仁兵) Chin. Phys. B, 2019, 28 (1):  010308.  DOI: 10.1088/1674-1056/28/1/010308 Abstract ( 630 )   HTML   PDF (2452KB) ( 187 )   We consider a binary dipolar Bose-Einstein condensate confined in a rotating harmonic plus quartic potential trap. The ground-state vortex structures are numerically obtained as a function of the contact interactions and the dipole-dipole interaction in both slow and rapid rotation cases. The results show that the vortex configurations depend strongly on the strength of the contact interactions, the relative strength between dipolar and contact interactions, as well as on the orientation of the dipoles. A variety of exotic ground-state vortex structures, such as pentagonal and hexagon vortex lattice, square vortex lattice with a central vortex, annular vortex lines, and straight vortex lines, are observed by turning such controllable parameters. Our results deepen the understanding of effects of dipole-dipole interaction on the topological defects.

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Solitons in nonlinear systems and eigen-states in quantum wells Li-Chen Zhao(赵立臣), Zhan-Ying Yang(杨战营), Wen-Li Yang(杨文力) Chin. Phys. B, 2019, 28 (1):  010501.  DOI: 10.1088/1674-1056/28/1/010501 Abstract ( 998 )   HTML   PDF (630KB) ( 234 )   We study the relations between solitons of nonlinear Schrödinger equation and eigen-states of linear Schrödinger equation with some quantum wells. Many different non-degenerated solitons are re-derived from the eigen-states in the quantum wells. We show that the vector solitons for the coupled system with attractive interactions correspond to the identical eigen-states with the ones of the coupled systems with repulsive interactions. Although their energy eigenvalues seem to be different, they can be reduced to identical ones in the same quantum wells. The non-degenerated solitons for multi-component systems can be used to construct much abundant degenerated solitons in more components coupled cases. Meanwhile, we demonstrate that soliton solutions in nonlinear systems can also be used to solve the eigen-problems of quantum wells. As an example, we present the eigenvalue and eigen-state in a complicated quantum well for which the Hamiltonian belongs to the non-Hermitian Hamiltonian having parity-time symmetry. We further present the ground state and the first exited state in an asymmetric quantum double-well from asymmetric solitons. Based on these results, we expect that many nonlinear physical systems can be used to observe the quantum states evolution of quantum wells, such as a water wave tank, nonlinear fiber, Bose-Einstein condensate, and even plasma, although some of them are classical physical systems. These relations provide another way to understand the stability of solitons in nonlinear Schrödinger equation described systems, in contrast to the balance between dispersion and nonlinearity.

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Attractors with controllable basin sizes from cooperation of contracting and expanding dynamics in pulse-coupled oscillators Hai-Lin Zou(邹海林) Zi-Chen Deng(邓子辰) Chin. Phys. B, 2019, 28 (1):  010502.  DOI: 10.1088/1674-1056/28/1/010502 Abstract ( 752 )   HTML   PDF (1741KB) ( 183 )   Unstable attractors are a novel type of attractor with local unstable dynamics, but with positive measures of basins. Here, we introduce local contracting dynamics by slightly modifying the function which mediates the interactions among the oscillators. Thus, the property of unstable attractors can be controlled through the cooperation of expanding and contracting dynamics. We demonstrate that one certain type of unstable attractor is successfully controlled through this simple modification. Specifically, the staying time for unstable attractors can be prolonged, and we can even turn the unstable attractors into stable attractors with predictable basin sizes. As an application, we demonstrate how to realize the switching dynamics that is only sensitive to the finite size perturbations.

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Evacuation simulation considering action of guard in artificial attack Chang-Kun Chen(陈长坤), Yun-He Tong(童蕴贺) Chin. Phys. B, 2019, 28 (1):  010503.  DOI: 10.1088/1674-1056/28/1/010503 Abstract ( 816 )   HTML   PDF (1330KB) ( 159 )   To investigate the evacuation behaviors of pedestrians considering the action of guards and to develop an effective evacuation strategy in an artificial attack, an extended floor field model is proposed. In this model, the artificial attacker's assault on pedestrians, the death of pedestrians, and the guard's capture are involved simultaneously. An alternative evacuation strategy which can largely reduce the number of casualties is developed and the effects of several key parameters such as the deterrence radius and capture distance on evacuation dynamics are studied. The results show that congestion near the exit has dual effects. More specifically, the guard can catch all attackers in a short time because the artificial attackers have a more concentrated distribution, but more casualties can occur because it is hard for pedestrians to escape the assault due to congestion. In contrast, when pedestrians have more preference of approaching the guard, although the guard will take more time to capture the attackers resulting from the dispersion of the attackers, the death toll will decrease. One of the reasons is the dispersal of the crowd, and the decrease in congestion is beneficial for escape. The other is that the attackers will be caught before launching the attack on the people who are around the guard, in other words, the guard protects a large number of pedestrians from being killed. Moreover, increasing capture distance of the guard can effectively reduce the casualties and the catch time. As the deterrence radius reflecting the tendency of escaping from the guard for attackers rises, it becomes more difficult for the guard to catch the attackers and more casualties are caused. However, when the deterrence radius reaches a certain level, the number of deaths is reduced because the attackers prefer to stay as far away as possible from the guard rather than occupy a position where they could assault more people.

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Formation mechanism of asymmetric breather and rogue waves in pair-transition-coupled nonlinear Schrödinger equations Zai-Dong Li(李再东), Yang-yang Wang(王洋洋), Peng-Bin He(贺鹏斌) Chin. Phys. B, 2019, 28 (1):  010504.  DOI: 10.1088/1674-1056/28/1/010504 Abstract ( 872 )   HTML   PDF (3554KB) ( 153 )   Based on the developed Darboux transformation, we investigate the exact asymmetric solutions of breather and rogue waves in pair-transition-coupled nonlinear Schrödinger equations. As an example, some types of exact breather solutions are given analytically by adjusting the parameters. Moreover, the interesting fundamental problem is to clarify the formation mechanism of asymmetry breather solutions and how the particle number and energy exchange between the background and soliton ultimately form the breather solutions. Our results also show that the formation mechanism from breather to rogue wave arises from the transformation from the periodic total exchange into the temporal local property.

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Effect of exit location on flow of mice under emergency condition Teng Zhang(张腾), Shen-Shi Huang(黄申石), Xue-Lin Zhang(张学林), Shou-Xiang Lu(陆守香), Chang-Hai Li(黎昌海) Chin. Phys. B, 2019, 28 (1):  010505.  DOI: 10.1088/1674-1056/28/1/010505 Abstract ( 603 )   HTML   PDF (2113KB) ( 114 )   The evacuation of crowds in a building has always emerged as a vital issue in many accidents. The geometrical structure of a room, especially the exit design has a great influence on crowd evacuation under emergency conditions. In this paper, the effect of exit location of a room on crowd evacuation in an emergency is investigated with mice. Two different exits are set in a rectangular chamber. One is located in the middle of a wall (middle-exit) and the other is at the corner of the chamber (corner-exit). Arching and clogging are observed in the flow of mice. The result based on the escape trajectories of mice shows a dynamic balance in the arch near the exit wherever the exit is located. We demonstrate that the occupant position in the arch has an effect on the escape sequence of mice. At a low stimulation level, the narrow middle-exit is more effective in increasing the flow rate of mice than the narrow corner-exit. However, the opposite result appears when the exit becomes wider. At a high stimulation level, the effect of exit location on flow of mice tends to be weakened. The results suggest that the specific level of stimulation needs to be taken into account when optimizing the evacuation efficiency of a crowd through the geometrical structure of a room.

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Simulation of SiC radiation detector degradation Hai-Li Huang(黄海栗), Xiao-Yan Tang(汤晓燕), Hui Guo(郭辉), Yi-Men Zhang(张义门), Yu-Tian Wang(王雨田), Yu-Ming Zhang(张玉明) Chin. Phys. B, 2019, 28 (1):  010701.  DOI: 10.1088/1674-1056/28/1/010701 Abstract ( 698 )   HTML   PDF (580KB) ( 167 )   Simulation on the degradation of 4H-SiC Schottky detector was carried out using ISE TCAD, and the limit of the drift-diffusion analytical model was discussed. Two independent defect levels, rather than a pair of specific carrier lifetime, were induced to describe Z1/2 defects in simulation to calculate the charge collection efficiency versus bias voltage. Comparison between our calculation and the reported experimental results shows that an acceptable agreement was achieved, proving the feasibility of regarding Z1/2 defect as two individual defect levels. Such a treatment can simplify the simulation and may help to further investigate the detector degradation.

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Standing-wave spectrometry in silicon nano-waveguides using reflection-based near-field scanning optical microscopy Yi-Zhi Sun(孙一之), Wei Ding(丁伟), Bin-Bin Wang(王斌斌), Rafael Salas-Montiel, Sylvain Blaize, Renaud Bachelot, Zhong-Wei Fan(樊仲维), Li-Shuang Feng(冯丽爽) Chin. Phys. B, 2019, 28 (1):  010702.  DOI: 10.1088/1674-1056/28/1/010702 Abstract ( 580 )   HTML   PDF (620KB) ( 186 )   Utilizing reflection-based near-field scanning optical microscopy (NSOM) to image and analyze standing-wave patterns, we present a characterization technique potentially suitable for complex photonic integrated circuits. By raster scanning along the axis of a straight nano-waveguide in tapping mode and sweeping wavelength, detailed information of propagating waves in that waveguide has been extracted from analyses in both space and wavelength domains. Our technique needs no special steps for phase stabilization, thus allowing long-duration and environment-insensitive measurements. As a proof-of-concept test, in a silicon single-mode waveguide with a few of etched holes, the locations and reflection strengths of the inner defects have been quantified. The measurement uncertainty of the reflection amplitude is less than 25% at current stage. Our technique paves the way for non-destructively diagnosing photonic circuits on a chip with sub-wavelength spatial resolution and detailed information extraction.

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H∞ couple-group consensus of stochastic multi-agent systems with fixed and Markovian switching communication topologies Muyun Fang(方木云), Cancan Zhou(周灿灿), Xin Huang(黄鑫), Xiao Li(李晓), Jianping Zhou(周建平) Chin. Phys. B, 2019, 28 (1):  010703.  DOI: 10.1088/1674-1056/28/1/010703 Abstract ( 782 )   HTML   PDF (598KB) ( 275 )   The paper addresses the issue of H∞ couple-group consensus for a class of discrete-time stochastic multi-agent systems via output-feedback control. Both fixed and Markovian switching communication topologies are considered. By employing linear transformations, the closed-loop systems are converted into reduced-order systems and the H∞ couple-group consensus issue under consideration is changed into a stochastic H∞ control problem. New conditions for the mean-square asymptotic stability and H∞ performance of the reduced-order systems are proposed. On the basis of these conditions, constructive approaches for the design of the output-feedback control protocols are developed for the fixed communication topology and the Markovian switching communication topologies, respectively. Finally, two numerical examples are given to illustrate the applicability of the present design approaches.

ATOMIC AND MOLECULAR PHYSICS

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First-principles study of structural, electronic, elastic, and thermal properties of Imm2-BC Qiang Li(李强), Zhen-Ling Wang(王振玲), Yu-Cheng Yu(于玉城), Lan Ma(马兰), Shao-Li Yang(杨绍利), Hai-Bo Wang(王海波), Rui Zhang(张锐) Chin. Phys. B, 2019, 28 (1):  013101.  DOI: 10.1088/1674-1056/28/1/013101 Abstract ( 746 )   HTML   PDF (1710KB) ( 175 )   Using the first-principles method, we predict an orthorhombic boron-carbon binary structure with space group Imm2. This structure is verified to be dynamically and mechanically stable, and possesses a cavity of 27.5 Å2 that makes it a potential molecular sieve material. The C sp2 and sp3 hybridized bonding in Imm2 BC is an important factor for its structural stability. The energy band calculations reveal that Imm2 BC is a semiconductor with a band gap of 1.3 eV and has a promising application in the electro-optic field. The lattice thermal conductivity along the crystal [100] direction at room temperature is 186 W·m-1·K-1, that is about 5 times higher than those along the [010] and [001] directions, which stems from the different group velocity along the crystal direction. Moreover, the acoustic-optical coupling is important for heat transport in Imm2 BC, and the contribution of optical phonons to lattice thermal conductivity in the [100], [010], and [001] directions is 49%, 59%, and 61%, respectively. This study gives a fundamental understanding of the structural, electronic, elastic, and heat transport properties in Imm2 BC, further enriching the family of boron-carbon binary compounds.

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Validity of extracting photoionization time delay from the first moment of streaking spectrogram Chang-Li Wei(魏长立), Xi Zhao(赵曦) Chin. Phys. B, 2019, 28 (1):  013201.  DOI: 10.1088/1674-1056/28/1/013201 Abstract ( 686 )   HTML   PDF (1799KB) ( 135 )   Photoionization time delays have been studied in many streaking experiments in which an attosecond pulse is used to ionize the atomic or solid state target in the presence of a dressing infrared laser field. Among the methods of extracting the time delay from the streaking spectrogram, the simplest one is to calculate the first moment of the spectrogram and to measure its offset relative to the vector potential of the infrared field. The first moment method has been used in many theoretical simulations and analysis of experimental data, but the meaning of this offset needs to be investigated. We simulate the spectrograms and compare the extracted time delay from the first moment with the input Wigner delay. In this study, we show that the first moment method is valid only when the group delay dispersions corresponding to both the spectral phase of the attosecond pulse and the phase of the single-photon transition dipole matrix element of the target are small. Under such circumstance, the electron wave packet behaves like a classical particle and the extracted time delay can be related to a group delay in the photoionization process. To avoid ambiguity and confusion, we also suggest that the photoionization time delay be replaced by photoionization group delay and the Wigner time delay be replaced by Wigner group delay.

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Properties of collective Rabi oscillations with two Rydberg atoms Dan-Dan Ma(马丹丹), Ke-Ye Zhang(张可烨), Jing Qian(钱静) Chin. Phys. B, 2019, 28 (1):  013202.  DOI: 10.1088/1674-1056/28/1/013202 Abstract ( 734 )   HTML   PDF (2262KB) ( 182 )   Motivated by experimental advances that the collective excitation of two Rydberg atoms was observed, we provide an elaborate theoretical study for the dynamical behavior of two-atom Rabi oscillations. In the large-intermediate-detuning case, the two-photon Rabi oscillation is found to be significantly affected by the strength of the interatomic van der Waals interaction. With a careful comparison of the exact numbers and values of the oscillation frequency, we propose a new way to determine the strength of excitation blockade, agreeing well with the previous universal criterion for full, partial, and no blockade regions. In the small-intermediate-detuning case, we find a blockade-like effect, but the collective enhancement factor is smaller than √2 due to the quantum interference of double optical transitions involving the intermediate state. Moreover, a fast two-photon Rabi oscillation in ns timescale is manifested by employing intense lasers with an intensity of ~MW/cm2, offering a possibility of ultrafast control of quantum dynamics with Rydberg atoms.

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Accurate calculation of electron affinity for S3 Xue Yang(杨雪), Haifeng Xu(徐海峰), Bing Yan(闫冰) Chin. Phys. B, 2019, 28 (1):  013203.  DOI: 10.1088/1674-1056/28/1/013203 Abstract ( 813 )   HTML   PDF (359KB) ( 139 )   The accurate equilibrium structures of S3 and S3- are determined by the coupled-cluster method with single, double excitation and perturbative triple excitation (CCSD(T)) with basis sets of aug-cc-pV(n+d)Z (n=T, Q, 5, or 6), complete basis set extrapolation functions with two-parameters and three-parameters, together with considering the contributions due to the core-valence electron correlation, scalar relativistic effects, spin-orbit coupling, and zero-point vibrational corrections. Our calculations show that both the neutral S3 and anion S3- have open forms with C2v symmetry. On the basis of the stable geometries, the adiabatic electron affinity of S3 is determined to be 19041(11) cm-1, which is in excellent agreement with the experimental data (19059(7) cm-1). The dependence of geometries and electron affinity on the computation level and physical corrections is discussed. The present computational results are helpful to the experimental molecular spectroscopy and bonding of S3.

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Novel infrared differential optical absorption spectroscopy remote sensing system to measure carbon dioxide emission Ru-Wen Wang(王汝雯), Pin-Hua Xie(谢品华), Jin Xu(徐晋), Ang Li(李昂) Chin. Phys. B, 2019, 28 (1):  013301.  DOI: 10.1088/1674-1056/28/1/013301 Abstract ( 597 )   HTML   PDF (765KB) ( 171 )   A CO2 infrared remote sensing system based on the algorithm of weighting function modified differential optical absorption spectroscopy (WFM-DOAS) is developed for measuring CO2 emissions from pollution sources. The system is composed of a spectrometer with band from 900 nm to 1700 nm, a telescope with a field of view of 1.12°, a silica optical fiber, an automatic position adjuster, and the data acquisition and processing module. The performance is discussed, including the electronic noise of the charge-coupled device (CCD), the spectral shift, and detection limits. The resolution of the spectrometer is 0.4 nm, the detection limit is 8.5×1020 molecules·cm-2, and the relative retrieval error is < 1.5%. On May 26, 2018, a field experiment was performed to measure CO2 emissions from the Feng-tai power plant, and a two-dimensional distribution of CO2 from the plume was obtained. The retrieved differential slant column densities (dSCDs) of CO2 are around 2×1021 molecules·cm-2 in the unpolluted areas, 5.5×1021 molecules·cm-2 in the plume locations most strongly affected by local CO2 emissions, and the fitting error is less than 2×1020 molecules·cm-2, which proves that the infrared remote sensing system has the characteristics of fast response and high precision, suitable for measuring CO2 emission from the sources.

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Momentum-space crystal in narrow-line cooling of 87Sr Jian-Xin Han(韩建新), Ben-Quan Lu(卢本全), Mo-Juan Yin(尹默娟), Ye-Bing Wang(王叶兵), Qin-Fang Xu(徐琴芳), Xiao-Tong Lu(卢晓同), Hong Chang(常宏) Chin. Phys. B, 2019, 28 (1):  013701.  DOI: 10.1088/1674-1056/28/1/013701 Abstract ( 663 )   HTML   PDF (1460KB) ( 150 )   The discovery of the momentum space crystal based on the alkaline-earth atom 88Sr in narrow-line cooling has paved the way to explore this novel physical phenomenon in other cold atom systems. In this paper, a momentum space crystal based on the fermions 87Sr in narrow-line cooling of transition 1S0-3P1 is demonstrated. We theoretically analyze and compare the formation principle of the narrow-line with that of broad-line cooling, and achieve the momentum space crystal in experiment. Beyond that we present a series of numerical calculations of those important parameters which influence the distribution and size of the momentum space crystal. Correspondingly, we vary the values of these parameters in experiment to observe the momentum space crystal evolution and distribution. The experimental results are in conformity with the results of the theoretically numerical calculations. These results and analyses provide a detailed supplementary study on the formation and evolution of momentum space crystal. In addition, this work could also give a guideline on atomic manipulation by narrow-line cooling.

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Effect of external magnetic field on the shift of resonant frequency in photoassociation of ultracold Cs atoms Pengwei Li(李鹏伟), Yuqing Li(李玉清), Guosheng Feng(冯国胜), Jizhou Wu(武寄洲), Jie Ma(马杰), Liantuan Xiao(肖连团), Suotang Jia(贾锁堂) Chin. Phys. B, 2019, 28 (1):  013702.  DOI: 10.1088/1674-1056/28/1/013702 Abstract ( 590 )   HTML   PDF (828KB) ( 120 )   We study the influence of external magnetic field on the shift of the resonant frequency in the photoassociation of ultracold Cs atoms, which are captured in a magnetically levitated optical crossed dipole trap. With the increase of the photoassociation laser intensity, the linear variation of the frequency shift is measured by recording the photoassociation spectra of the long-range 0u+ state of Cs molecule below the 6S1/2+6P1/2 dissociation limit at different magnetic fields. The slope of the frequency shift to the intensity of the photoassociation laser exhibits a strong dependence on the external magnetic field. The experimental data is simulated with an analytic theory model, in which a single channel rectangular potential with the tunable well depth is introduced to acquire the influence of the magnetic field on the atomic behavior in the effective range where photoassociation occurs.

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

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Propagation characteristics of oblique incidence terahertz wave through non-uniform plasma Antao Chen(陈安涛), Haoyu Sun(孙浩宇), Yiping Han(韩一平), Jiajie Wang(汪加洁), Zhiwei Cui(崔志伟) Chin. Phys. B, 2019, 28 (1):  014201.  DOI: 10.1088/1674-1056/28/1/014201 Abstract ( 772 )   HTML   PDF (1513KB) ( 258 )   The propagation characteristics of oblique incidence terahertz (THz) waves through non-uniform plasma are investigated by the shift-operator finite-difference time-domain (SO-FDTD) method combined with the phase matching condition. The electron density distribution of the non-uniform plasma is assumed to be in a Gaussian profile. Validation of the present method is performed by comparing the results with those obtained by an analytical method for a homogeneous plasma slab. Then the effects of parameters of THz wave and plasma layer on the propagation properties are analyzed. It is found that the transmission coefficients greatly depend on the incident angle as well as on the thickness of the plasma, while the polarization of the incident wave has little influence on the propagation process in the range of frequency considered in this paper. The results confirm that the THz wave can pass through the plasma sheath effectively under certain conditions, which makes it a potential candidate to overcome the ionization blackout problem.

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Effects of the Casimir force on the properties of a hybrid optomechanical system Yi-Ping Wang(王一平), Zhu-Cheng Zhang(张筑城), Ya-Fei Yu(於亚飞), Zhi-Ming Zhang(张智明) Chin. Phys. B, 2019, 28 (1):  014202.  DOI: 10.1088/1674-1056/28/1/014202 Abstract ( 638 )   HTML   PDF (496KB) ( 191 )   We investigate the effects of the Casimir force on the output properties of a hybrid optomechanical system. In this system, a nanosphere is fixed on the movable-mirror side of the standard optomechanical system, and the nanosphere interacts with the movable-mirror via the Casimir force, which depends on the mirror-sphere separation. In the presence of the probe and control fields, we analyze the transmission coefficient and the group delay of the field-component with the frequency of the probe field. We also study the transmission intensity of the field-component with the frequency of a newly generated four-wave mixing (FWM) field. By manipulating the Casimir force, we find that a tunable slow light can be realized for the field-component with the frequency of the probe field, and the intensity spectrum of the FWM field can be enhanced and shifted effectively.

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Wavefront evolution of the signal beam in Ti: sapphire chirped pulse amplifier Zhen Guo(郭震), Lianghong Yu(於亮红), Wenqi Li(李文启), Zebiao Gan(甘泽彪), Xiaoyan Liang(梁晓燕) Chin. Phys. B, 2019, 28 (1):  014203.  DOI: 10.1088/1674-1056/28/1/014203 Abstract ( 800 )   HTML   PDF (939KB) ( 192 )   We studied the evolution of wavefront aberration (WFA) of a signal beam during amplification in a Ti:sapphire chirped pulse amplification (CPA) system. The results verified that the WFA of the amplified laser beam has little relation with the change of the pump beam energies. Transverse parasitic lasing that might occur in CPA hardly affects the wavefront of the signal beam. Thermal effects were also considered in this study, and the results show that the thermal effect cumulated in multiple amplification processes also has no obvious influence on the wavefront of the signal beam for a single-shot frequency. The results presented in this paper confirmed experimentally that the amplification in a Ti:sapphire CPA system has little impact on the WFA of the signal beam and it is very helpful for wavefront correction of single-shot PW and multi-PW laser systems based on Ti:sapphire.

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Multiple Fano resonances in nanorod and nanoring hybrid nanostructures Xijun Wu(吴希军), Ceng Dou(窦层), Wei Xu(徐伟), Guangbiao Zhang(张广彪), Ruiling Tian(田瑞玲), Hailong Liu(刘海龙) Chin. Phys. B, 2019, 28 (1):  014204.  DOI: 10.1088/1674-1056/28/1/014204 Abstract ( 647 )   HTML   PDF (1057KB) ( 235 )   Multiple Fano resonances of plasmonic nanostructures have attracted much attention due to their potential applications in multicomponent biosensing. In this paper, we propose a series of hybridized nanostructures consisting of a single nanoring and multiple nanorods to generate multiple Fano resonances. One to three Fano resonances are achieved through tuning the number of nanorods. The interaction coupling process between different components of the nanostructures is recognized as the mechanism of multiple Fano resonances. We also theoretically investigate the applications of the produced multiple Fano resonances in refractive index sensing. The specific properties of multiple Fano resonances will make our proposed nanostructures beneficial to high-sensitivity biosensors.

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Controllable transmission of vector beams in dichroic medium Yun-Ke Li(李云珂), Jin-Wen Wang(王金文), Xin Yang(杨欣), Yun Chen(陈云), Xi-Yuan Chen(陈熙远), Ming-Tao Cao(曹明涛), Dong Wei(卫栋), Hong Gao(高宏), Fu-Li Li(李福利) Chin. Phys. B, 2019, 28 (1):  014205.  DOI: 10.1088/1674-1056/28/1/014205 Abstract ( 713 )   HTML   PDF (1567KB) ( 181 )   Vector beams with spatially varying polarization distribution in the wavefront plane have received increasing attention in recent years. The manipulation of vector beams both in intensity and polarization distributions is highly desired and under development. In this work, we study the transmission property of vector beams through warm rubidium vapor and realize controllable transmission of vector beams based on atomic dichroism. By utilizing the linearly polarized beam and vector beams as the pump and probe beams in a pump-probe configuration, a spatially-dependent dichroism can be obtained, which leads to spatially varied absorption of the probe beam. The controllable intensity distribution of the probe beam, as a two-petal pattern, can rotate with the variation of the pump beam's polarization states. We experimentally demonstrate the mechanism of dichroism with linear polarization light and provide an explanation based on the optical pumping effect. Alternatively, the varying trend of the probe beam's intensity is also interpreted by utilizing the Jones matrix. Our results are thus beneficial for providing potential applications in optical manipulation in atomic ensembles.

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Experimental determination of distributions of soot particle diameter and number density by emission and scattering techniques Huawei Liu(柳华蔚), Shu Zheng(郑树) Chin. Phys. B, 2019, 28 (1):  014206.  DOI: 10.1088/1674-1056/28/1/014206 Abstract ( 768 )   HTML   PDF (1382KB) ( 172 )   A diagnostics method was presented that uses emission and scattering techniques to simultaneously determine the distributions of soot particle diameter and number density in hydrocarbon flames. Two manta G-504C cameras were utilized for the scattering measurement, with consideration of the attenuation effect in the flames according to corresponding absorption coefficients. Distributions of soot particle diameter and number density were simultaneously determined using the measured scattering coefficients and absorption coefficients under multiple wavelengths already measured with a SOC701V hyper-spectral imaging device, according to the Mie scattering theory. A flame was produced using an axisymmetric laminar diffusion flame burner with 194 mL/min ethylene and 284 L/min air, and distributions of particle diameter and number density for the flame were presented. Consequently, the distributions of soot volume fraction were calculated using these two parameters as well, which were in good agreement with the results calculated according to the Rayleigh approximation, demonstrating that the proposed diagnostic method is capable of simultaneous determination of the distributions of soot particle diameter and number density.

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Mode-locked fiber laser with MoSe2 saturable absorber based on evanescent field Ren-Li Zhang(张仁栗), Jun Wang(王俊), Xiao-Yan Zhang(张晓艳), Jin-Tian Lin(林锦添), Xia Li(李夏), Pei-Wen Kuan(关珮雯), Yan Zhou(周延), Mei-Song Liao(廖梅松), Wei-Qing Gao(高伟清) Chin. Phys. B, 2019, 28 (1):  014207.  DOI: 10.1088/1674-1056/28/1/014207 Abstract ( 812 )   HTML   PDF (650KB) ( 232 )   An all-fiber mode-locked fiber laser was achieved with a saturable absorber based on a tapered fiber deposited with layered molybdenum selenide (MoSe2). The laser was operated at a central wavelength of 1558.35 nm with an output spectral width of 2.9 nm, and a pulse repetition rate of 16.33 MHz. To the best of our knowledge, this is the first report on mode-locked fiber lasers using MoSe2 saturable absorbers based on tapered fibers.

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High performance GaSb based digital-grown InGaSb/AlGaAsSb mid-infrared lasers and bars Hot! Sheng-Wen Xie(谢圣文), Yu Zhang(张宇), Cheng-Ao Yang(杨成奥), Shu-Shan Huang(黄书山), Ye Yuan(袁野), Yi Zhang(张一), Jin-Ming Shang(尚金铭), Fu-Hui Shao(邵福会), Ying-Qiang Xu(徐应强), Hai-Qiao Ni(倪海桥), Zhi-Chuan Niu(牛智川) Chin. Phys. B, 2019, 28 (1):  014208.  DOI: 10.1088/1674-1056/28/1/014208 Abstract ( 1232 )   HTML   PDF (580KB) ( 388 )   InGaSb/AlGaAsSb double-quantum-well diode lasers emitting around 2 μm are demonstrated. The AlGaAsSb barriers of the lasers are grown with digital alloy techniques consisting of binary AlSb/AlAs/GaSb short-period pairs. Peak power conversion efficiency of 26% and an efficiency higher than 16% at 1 W are achieved at continuous-wave operation for a 2-mm-long and 100-μm-wide stripe laser. The maximum output power of a single emitter reaches to 1.4 W at 7 A. 19-emitter bars with maximum efficiency higher than 20% and maximum power of 16 W are fabricated. Lasers with the short-period-pair barriers are proved to have improved temperature properties and wavelength stabilities. The characteristic temperature (T0) is up to 140℃ near room temperature (25-55℃).

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Theoretical prediction of the yield of strong oxides under acoustic cavitation Jing Sun(孙晶), Zhuangzhi Shen(沈壮志), Runyang Mo(莫润阳) Chin. Phys. B, 2019, 28 (1):  014301.  DOI: 10.1088/1674-1056/28/1/014301 Abstract ( 693 )   HTML   PDF (681KB) ( 193 )   Considering liquid viscosity, surface tension, and liquid compressibility, the effects of dynamical behaviors of cavitation bubbles on temperature and the amount of oxides inside the bubble are numerically investigated by acoustic field, regarding water as a work medium. The effects of acoustic frequency, acoustic pressure amplitude, and driving waveforms on bubble temperature and the number of oxides inside the bubbles by rapid collapse of cavitation bubbles are analysed. The results show that the changes of acoustic frequency, acoustic pressure amplitude, and driving waveforms not only have an effect on temperature and the number of oxides inside the bubble, but also influence the degradation species of pollution, which provides guidance for improving the degradation of water pollution.

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Effects of rough surface on sound propagation in shallow water Ruo-Yun Liu(刘若芸), Zheng-Lin Li(李整林) Chin. Phys. B, 2019, 28 (1):  014302.  DOI: 10.1088/1674-1056/28/1/014302 Abstract ( 844 )   HTML   PDF (978KB) ( 260 )   Underwater acoustic applications depend critically on the prediction of sound propagation, which can be significantly affected by a rough surface, especially in shallow water. This paper aims to investigate how randomly fluctuating surface influences transmission loss (TL) in shallow water. The one-dimension wind-wave spectrum, Monterey-Miami parabolic equation (MMPE) model, Monte Carlo method, and parallel computing technology are combined to investigate the effects of different sea states on sound propagation. It is shown that TL distribution properties are related to the wind speed, frequency, range, and sound speed profile. In a homogenous waveguide, with wind speed increasing, the TLs are greater and more dispersive. For a negative thermocline waveguide, when the source is above the thermocline and the receiver is below that, the effects of the rough surface are the same and more significant. When the source and receiver are both below the thermocline, the TL distributions are nearly the same for different wind speeds. The mechanism of the different TL distribution properties in the thermocline environment is explained by using ray theory. In conclusion, the statistical characteristics of TL are affected by the relative roughness of the surface, the interaction strength of the sound field with the surface, and the changes of propagating angle due to refraction.

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Derivation of lattice Boltzmann equation via analytical characteristic integral Huanfeng Ye(叶欢锋), Bo Kuang(匡波), Yanhua Yang(杨燕华) Chin. Phys. B, 2019, 28 (1):  014701.  DOI: 10.1088/1674-1056/28/1/014701 Abstract ( 718 )   HTML   PDF (814KB) ( 189 )   A lattice Boltzmann (LB) theory, the analytical characteristic integral (ACI) LB theory, is proposed in this paper. ACI LB theory takes the Bhatnagar-Gross-Krook (BGK)-Boltzmann equation as the exact kinetic equation behind Navier-Stokes continuum and momentum equations and constructs an LB equation by rigorously integrating the BGK-Boltzmann equation along characteristics. It is a general theory, supporting most existing LB equations including the standard lattice BGK (LBGK) equation inherited from lattice-gas automata, whose theoretical foundation had been questioned. ACI LB theory also indicates that the characteristic parameter of an LB equation is collision number, depicting the particle-interaction intensity in the time span of the LB equation, instead of the traditionally assumed relaxation time, and the over-relaxation time problem is merely a manifestation of the temporal evolution of equilibrium distribution along characteristics under high collision number, irrelevant to particle kinetics. In ACI LB theory, the temporal evolution of equilibrium distribution along characteristics is the determinant of LB method accuracy and we numerically prove this.

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Double-slit interference of a relativistic vortex laser Hao Zhang(张浩), Bai-Fei Shen(沈百飞), Lin-Gang Zhang(张林港) Chin. Phys. B, 2019, 28 (1):  014702.  DOI: 10.1088/1674-1056/28/1/014702 Abstract ( 743 )   HTML   PDF (914KB) ( 218 )   The interference of a relativistic vortex laser is investigated for the case when a linearly polarized Laguerre-Gaussian pulse impinges on a double-slit solid target. Three-dimensional particle-in-cell simulation results show that the interference fringes of high-order harmonics are twisted, similar to that of the fundamental vortex laser. The twisting order of the interference pattern is determined by the order of the vortex high-order harmonics, which can be explained by the classic double-slit interference models. The usual double-slit interference has been extended to the regime of relativistic intensity, which may have potential applications for measuring the topological charge of vortex high-order harmonics.

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Molecular-dynamics investigation of the simple droplet critical wetting behavior at a stripe pillar edge defect Xiaolong Liu(刘小龙), Chengyun Hong(洪成允), Yong Ding(丁勇), Xuepeng Liu(刘雪朋), Jianxi Yao(姚建曦), Songyuan Dai(戴松元) Chin. Phys. B, 2019, 28 (1):  014703.  DOI: 10.1088/1674-1056/28/1/014703 Abstract ( 862 )   HTML   PDF (1410KB) ( 244 )   The microscopic stripe pillar is one of the most frequently adopted building blocks for hydrophobic substrates. However, at high temperatures the particles on the droplet surface readily evaporate and re-condense on the pillar sidewall, which makes the droplet highly unstable and undermines the overall hydrophobic performance of the pillar. In this work, molecular dynamics (MD) simulation of the simple liquid at a single stripe pillar edge defect is performed to characterize the droplet's critical wetting properties considering the evaporation-condensation effect. From the simulation results, the droplets slide down from the edge defect with a volume smaller than the critical value, which is attributed to the existence of the wetting layer on the stripe pillar sidewall. Besides, the analytical study of the pillar sidewall and wetting layer potential field distribution manifests the relation between the simulation parameters and the degree of the droplet pre-wetting, which agrees well with the MD simulation results.

PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

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Plasma shape optimization for EAST tokamak using orthogonal method Yuan-Yang Chen(陈远洋), Xiao-Hua Bao(鲍晓华), Peng Fu(傅鹏), Ge Gao(高格) Chin. Phys. B, 2019, 28 (1):  015201.  DOI: 10.1088/1674-1056/28/1/015201 Abstract ( 836 )   HTML   PDF (2611KB) ( 207 )   It is necessary to reduce the currents of poloidal field (PF) coils as small as possible, during the static equilibrium design procedure of Experimental Advanced Superconductive Tokamak (EAST). The quasi-snowflake (QSF) divertor configuration is studied in this paper. Starting from a standard QSF plasma equilibrium, a new QSF equilibrium with 300 kA total plasma current is designed. In order to reduce the currents of PF6 and PF14, the influence of plasma shape on PF coil current distribution is analyzed. A fixed boundary equilibrium solver based on a non-rigid plasma model is used to calculate the flux distribution and PF coil current distribution. Then the plasma shape parameters are studied by the orthogonal method. According to the result, the plasma shape is redefined, and the calculated equilibrium shows that the currents of PF6 and PF14 are reduced by 3.592 kA and 2.773 kA, respectively.

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Damped electrostatic ion acoustic solitary wave structures in quantum plasmas with Bohm potential and spin effects S Hussain, H Hasnain, Mahnaz Q. Haseeb Chin. Phys. B, 2019, 28 (1):  015202.  DOI: 10.1088/1674-1056/28/1/015202 Abstract ( 806 )   HTML   PDF (430KB) ( 194 )   Nonlinear properties of ion acoustic solitary waves are studied in the case of dense magnetized plasmas. The degenerate electrons with relative density effects from their spin states in the same direction and from equally probable up and down spinning states are taken up separately. Quantum statistical as well as quantum tunneling effects for both types of electrons are taken. The ions have large inertia and are considered classically, whereas the electrons are degenerate. The collisions of ions and electrons with neutral atoms are considered. We derive the deformed Korteweg de-Vries (DKdV) equation for small amplitude electrostatic potential disturbances by employing the reductive perturbation technique. The Runge-Kutta method is applied to solve numerically the DKdV equation. The analytical solution of DKdV is also presented with time dependence. We discuss the profiles for velocity, amplitude, and time variations in solitons for the cases when all the electrons are spinning in the same direction and for the case when there is equal probability of electrons having spin up and spin down. We have found that the wave is unstable because of the collisions between neutral gas molecules and the charged plasmas particles in the presence of degenerate electrons.

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Effects of resonant magnetic perturbation on the instability of single tearing mode with non-shear flow Le Wang(王乐), Ming Yang(阳明), Wen-Bin Lin(林文斌) Chin. Phys. B, 2019, 28 (1):  015203.  DOI: 10.1088/1674-1056/28/1/015203 Abstract ( 541 )   HTML   PDF (544KB) ( 179 )   Non-shear flow can change the O-point position of a magnetic island, and thus it may play an important role in the effects of resonant magnetic perturbation (RMP) on the single tearing mode. We employ the nonlinear magnetohydrodynamics model in a slab geometry to investigate how RMP affects the single tearing mode instability with non-shear flow. It is found that the driving and suppressing effects of RMP on single tearing mode instability will appear alternately. When the flow velocity is small, the suppressing effect plays a major role through the development of the mode, and the tearing mode instability will be suppressed. With the flow velocity increasing, the driving effect will increase, while the suppressing effect will decrease. When the two effects reach equilibrium, the tearing mode will become stable.

CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

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Photoluminescence of SiV centers in CVD diamond particles with specific crystallographic planes Ying-Shuang Mei(梅盈爽), Cheng-Ke Chen(陈成克), Mei-Yan Jiang(蒋梅燕), Xiao Li(李晓), Yin-Lan Ruan(阮银兰), Xiao-Jun Hu(胡晓君) Chin. Phys. B, 2019, 28 (1):  016101.  DOI: 10.1088/1674-1056/28/1/016101 Abstract ( 795 )   HTML   PDF (4329KB) ( 178 )   We prepared the isolated micrometer-sized diamond particles without seeding on the substrate in hot filament chemical vapor deposition. The diamond particles with specific crystallographic planes and strong silicon-vacancy (SiV) photoluminescence (PL) have been prepared by adjusting the growth pressure. As the growth pressure increases from 2.5 to 3.5 kPa, the diamond particles transit from composite planes of {100} and {111} to only smooth {111} planes. The {111}-faceted diamond particles present better crystal quality and stronger normalized intensity of SiV PL with a narrower bandwidth of 5 nm. Raman depth profiles show that the SiV centers are more likely to be formed on the near-surface areas of the diamond particles, which have poorer crystal quality and greater lattice stress than the inner areas. Complex lattice stress environment in the near-surface areas broadens the bandwidth of SiV PL peak. These results provide a feasible method to prepare diamond particles with specific crystallographic planes and stronger SiV PL.

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Effect of substrate type on Ni self-assembly process Xuzhao Chai(柴旭朝), Boyang Qu(瞿博阳), Yuechao Jiao(焦岳超), Ping Liu(刘萍), Yanxia Ma(马彦霞), Fengge Wang(王凤歌), Xiaoquan Li(李晓荃), Xiangqian Fang(方向前), Ping Han(韩平), Rong Zhang(张荣) Chin. Phys. B, 2019, 28 (1):  016102.  DOI: 10.1088/1674-1056/28/1/016102 Abstract ( 774 )   HTML   PDF (2449KB) ( 163 )   Ni self-assembly has been performed on GaN (0001), Si (111) and sapphire (0001) substrates. Scanning electron microscopy (SEM) images verify that the Si (111) substrate leads to failure of the Ni assembly due to Si-N interlayer formation; the GaN (0001) and sapphire (0001) substrates promote assembly of the Ni particles. This indicates that the GaN/sapphire (0001) substrates are fit for Ni self-assembly. For the Ni assembly process on GaN/sapphire (0001) substrates, three differences are observed from the x-ray diffraction (XRD) patterns:(i) Ni self-assembly on the sapphire (0001) needs a 900℃ annealing temperature, lower than that on the GaN (0001) at 1000℃, and loses the Ni network structure stage; (ii) the Ni particle shape is spherical for the sapphire (0001) substrate, and truncated-cone for the GaN (0001) substrate; and (iii) a Ni-N interlayer forms between the Ni particles and the GaN (0001) substrate, but an interlayer does not appear for the sapphire (0001) substrate. All these differences are attributed to the interaction between the Ni and the GaN/sapphire (0001) substrates. A model is introduced to explain this mechanism.

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Effects of deuteration on the structure of NH4H2PO4 crystals characterized by neutron diffraction Baoan Liu(刘宝安), Lili Zhu(朱丽丽), Fafu Liu(刘发付), Xun Sun(孙洵), Xiping Chen(陈喜平), Lei Xie(谢雷), Yuanhua Xia(夏元华), Guangai Sun(孙光爱), Xin Ju(巨新) Chin. Phys. B, 2019, 28 (1):  016103.  DOI: 10.1088/1674-1056/28/1/016103 Abstract ( 691 )   HTML   PDF (1166KB) ( 187 )   A series of deuterated ammonium dihydrogen phosphate (DADP) crystals were grown and their structures were investigated by using powder neutron diffraction method. In the entire composition range, the deuterated level in the crystals is lower compared with the aqueous growth solution. The deuterium segregation coefficient in the crystals decreases with increasing deuterium content of the solution. The deuterium content in the NH4+ group is higher than that in H2PO4- group. In addition, the variations of lattice parameters are shown here.

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High-pressure-induced phase transition in cinchomeronic acid polycrystalline form-I Ting-Ting Yan(颜婷婷), Dong-Yang Xi(喜冬阳), Jun-Hai Wang(王俊海), Xu-Feng Fan(樊旭峰), Ye Wan(万晔), Li-Xiu Zhang(张丽秀), Kai Wang(王凯) Chin. Phys. B, 2019, 28 (1):  016104.  DOI: 10.1088/1674-1056/28/1/016104 Abstract ( 623 )   HTML   PDF (1454KB) ( 174 )   Diamond anvil cells combined with Raman spectroscopy and angle-dispersive x-ray diffraction (ADXRD) were used to investigate the compression behavior of cinchomeronic acid (C7H5NO4, CA), a hydrogen-bonded polymorphs. The compression of form-I at approximately 6.5 GPa caused an irreversible phase transition that produced the new polymorph form-Ⅲ. Lattice and internal modes in the Raman spectra were analyzed to determine the modifications in the local environment of CA form-I molecules. The form-Ⅲ was indexed and refined to a low-symmetry triclinic structure with space group P1. The mechanism for the phase transition involved the reconstructions in the hydrogen-bonded networks in CA form-I.

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Versatile GaInO3-sheet with strain-tunable electronic structure, excellent mechanical flexibility, and an ideal gap for photovoltaics Hui Du(杜慧), Shijie Liu(刘世杰), Guoling Li(李国岭), Liben Li(李立本), Xueshen Liu(刘学深), Bingbing Liu(刘冰冰) Chin. Phys. B, 2019, 28 (1):  016105.  DOI: 10.1088/1674-1056/28/1/016105 Abstract ( 829 )   HTML   PDF (1250KB) ( 162 )   Due to many remarkable physical and chemical properties, two-dimensional (2D) nanomaterials have become a hot spot in the field of condensed matter physics. In this paper, we have studied the structural, mechanical, and electronic properties of the 2D GaInO3 system by first-principles method. We find that 2D GaInO3 can exist stably at ambient condition. Molecular dynamic simulations show that GaInO3-sheet has excellent thermal stability and is stable up to 1100 K. Electronic structural calculations show that GaInO3-sheet has a band gap of 1.56 eV, which is close to the ideal band gap of solar cell materials, demonstrating great potential in future photovoltaic application. In addition, strain effect studies show that the GaInO3-sheet structure always exhibits a direct band gap under biaxial compressive strain, and as the biaxial compressive strain increases, the band gap gradually decreases until it is converted into metal. While biaxial tensile strain can cause the 2D material to transform from a direct band gap semiconductor into an indirect band gap semiconductor, and even to metal. Our research expands the application of the GaInO3 system, which may have potential application value in electronic devices and solar energy.

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Electronic structures and optical properties of Si- and Sn-doped β-Ga2O3: A GGA+U study Jun-Ning Dang(党俊宁), Shu-wen Zheng(郑树文), Lang Chen(陈浪), Tao Zheng(郑涛) Chin. Phys. B, 2019, 28 (1):  016301.  DOI: 10.1088/1674-1056/28/1/016301 Abstract ( 835 )   HTML   PDF (1529KB) ( 404 )   The electronic structures and optical properties of β-Ga2O3 and Si- and Sn-doped β-Ga2O3 are studied using the GGA+U method based on density functional theory. The calculated bandgap and Ga 3d-state peak of β-Ga2O3 are in good agreement with experimental results. Si- and Sn-doped β-Ga2O3 tend to form under O-poor conditions, and the formation energy of Si-doped β-Ga2O3 is larger than that of Sn-doped β-Ga2O3 because of the large bond length variation between Ga-O and Si-O. Si- and Sn-doped β-Ga2O3 have wider optical gaps than β-Ga2O3, due to the Burstein-Moss effect and the bandgap renormalization effect. Si-doped β-Ga2O3 shows better electron conductivity and a higher optical absorption edge than Sn-doped β-Ga2O3, so Si is more suitable as a dopant of n-type β-Ga2O3, which can be applied in deep-UV photoelectric devices.

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Equation of state for aluminum in warm dense matter regime Kun Wang(王坤), Dong Zhang(张董), Zong-Qian Shi(史宗谦), Yuan-Jie Shi(石元杰), Tian-Hao Wang(王天浩), Yue Zhang(张阅) Chin. Phys. B, 2019, 28 (1):  016401.  DOI: 10.1088/1674-1056/28/1/016401 Abstract ( 665 )   HTML   PDF (577KB) ( 162 )   A semi-empirical equation of state model for aluminum in a warm dense matter regime is constructed. The equation of state, which is subdivided into a cold term, thermal contributions of ions and electrons, covers a broad range of phase diagram from solid state to plasma state. The cold term and thermal contribution of ions are from the Bushman-Lomonosov model, in which several undetermined parameters are fitted based on equation of state theories and specific experimental data. The Thomas-Fermi-Kirzhnits model is employed to estimate the thermal contribution of electrons. Some practical modifications are introduced to the Thomas-Fermi-Kirzhnits model to improve the prediction of the equation of state model. Theoretical calculation of thermodynamic parameters, including phase diagram, curves of isothermal compression at ambient temperature, melting, and Hugoniot, are analyzed and compared with relevant experimental data and other theoretical evaluations.

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Equation of state of LiCoO2 under 30 GPa pressure Yong-Qing Hu(户永清), Lun Xiong(熊伦), Xing-Quan Liu(刘兴泉), Hong-Yuan Zhao(赵红远), Guang-Tao Liu(刘广涛), Li-Gang Bai(白利刚), Wei-Ran Cui(崔巍然), Yu Gong(宫宇), Xiao-Dong Li(李晓东) Chin. Phys. B, 2019, 28 (1):  016402.  DOI: 10.1088/1674-1056/28/1/016402 Abstract ( 699 )   HTML   PDF (566KB) ( 196 )   LiCoO2 is one of the most important cathode materials for high energy density lithium ion batteries. The compressed behavior of LiCoO2 under high pressure has been investigated using synchrotron radiation x-ray diffraction. It is found that LiCoO2 maintains hexagonal symmetry up to the maximum pressure of 30.1 GPa without phase transition. The elastic modulus at ambient pressure is 159.5(2.2) GPa and its first derivative is 3.92(0.23). In addition, the high-pressure compression behavior of LiCoO2 has been studied by first principles calculations. The derived bulk modulus of LiCoO2 is 141.6 GPa.

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Alkyl group functionalization-induced phonon thermal conductivity attenuation in graphene nanoribbons Caiyun Wang(王彩云), Shuang Lu(鲁爽), Xiaodong Yu(于晓东), Haipeng Li(李海鹏) Chin. Phys. B, 2019, 28 (1):  016501.  DOI: 10.1088/1674-1056/28/1/016501 Abstract ( 679 )   HTML   PDF (1838KB) ( 188 )   We calculated the room-temperature phonon thermal conductivity and phonon spectrum of alkyl group-functionalized zigzag graphene nanoribbons (ZGNRs) with molecular dynamics simulations. The increase in both chain length and concentration of alkyl groups caused remarkable reduction of phonon thermal conductivity in functionalized ZGNRs. Phonon spectra analysis showed that functionalization of ZGNR with alkyl functional groups induced phonon-structural defect scattering, thus leading to the reduction of phonon thermal conductivity of ZGNR. Our study showed that surface functionalization is an effective routine to tune the phonon thermal conductivity of GNRs, which is useful in graphene thermal-related applications.

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Approximate expression of Young's equation and molecular dynamics simulation for its applicability Shu-Wen Cui(崔树稳), Jiu-An Wei(魏久安), Wei-Wei Liu(刘伟伟), Ru-Zeng Zhu(朱如曾), Qian Ping(钱萍) Chin. Phys. B, 2019, 28 (1):  016801.  DOI: 10.1088/1674-1056/28/1/016801 Abstract ( 651 )   HTML   PDF (652KB) ( 185 )   In 1805, Thomas Young was the first to propose an equation (Young's equation) to predict the value of the equilibrium contact angle of a liquid on a solid. On the basis of our predecessors, we further clarify that the contact angle in Young's equation refers to the super-nano contact angle. Whether the equation is applicable to nanoscale systems remains an open question. Zhu et al.[College Phys. 4 7 (1985)] obtained the most simple and convenient approximate formula, known as the Zhu-Qian approximate formula of Young's equation. Here, using molecular dynamics simulation, we test its applicability for nanodrops. Molecular dynamics simulations are performed on argon liquid cylinders placed on a solid surface under a temperature of 90 K, using Lennard-Jones potentials for the interaction between liquid molecules and between a liquid molecule and a solid molecule with the variable coefficient of strength a. Eight values of a between 0.650 and 0.825 are used. By comparison of the super-nano contact angles obtained from molecular dynamics simulation and the Zhu-Qian approximate formula of Young's equation, we find that it is qualitatively applicable for nanoscale systems.

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

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Photoluminescence in fluorescent 4H-SiC single crystal adjusted by B, Al, and N ternary dopants Hot! Shi-Yi Zhuo(卓世异), Xue-Chao Liu(刘学超), Wei Huang(黄维), Hai-Kuan Kong(孔海宽), Jun Xin(忻隽), Er-Wei Shi(施尔畏) Chin. Phys. B, 2019, 28 (1):  017101.  DOI: 10.1088/1674-1056/28/1/017101 Abstract ( 874 )   HTML   PDF (455KB) ( 257 )   This paper reports the sensitive effect of photoluminescence peak intensity and transmittance affected by B, Al, and N dopants in fluorescent 4H-SiC single crystals. The crystalline type, doping concentration, photoluminescence spectra, and transmission spectra were characterized at room temperature. It is found that the doped 4H-SiC single crystal emits a warm white light covering a wide range from 460 nm to 720 nm, and the transmittance increases from ~10% to ~60% with the fluctuation of B, Al, and N ternary dopants. With a parameter of CD-A, defined by B, Al, and N concentration, the photoluminescence and transmittance properties can be adjusted by optimal doping regulation.

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Tunable magnetic orders in UAu1-xSb2 Wen Zhang(张文), Qiu-Yun Chen(陈秋云), Dong-Hua Xie(谢东华), Yi Liu(刘毅), Shi-Yong Tan(谭世勇), Wei Feng(冯卫), Xie-Gang Zhu(朱燮刚), Qun-Qing Hao(郝群庆), Yun Zhang(张云), Li-Zhu Luo(罗丽珠), Xin-Chun Lai(赖新春) Chin. Phys. B, 2019, 28 (1):  017102.  DOI: 10.1088/1674-1056/28/1/017102 Abstract ( 692 )   HTML   PDF (1797KB) ( 140 )   Two nonstoichiometric UAu1-xSb2 (x=0.25, 0.1) single crystals are successfully synthesized using a flux method, and their physical properties are comprehensively studied by measuring the dc-magnetization and electrical resistivity. Evidence for at least three magnetic phases is found in these samples. In zero field, both samples undergo an antiferromagnetic transition at a relatively high temperature, and with further cooling they pass through another antiferromagnetic phase, before reaching a ferromagnetic ground state. Furthermore, the magnetic order can be tuned by varying the site occupation of Au. Such a tunable magnetic order may provide an opportunity for exploring the potential quantum critical behavior in this system.

TOPICAL REVIEW—Photodetector: materials, physics, and applications

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Photodetectors based on two-dimensional materials and organic thin-film heterojunctions Jiayue Han(韩嘉悦), Jun Wang(王军) Chin. Phys. B, 2019, 28 (1):  017103.  DOI: 10.1088/1674-1056/28/1/017103 Abstract ( 731 )   HTML   PDF (6922KB) ( 671 )   High-performance photodetectors are expected to open up revolutionary opportunities in many application fields, such as environment monitoring, military, optical communication and biomedical science. Combining two-dimensional materials (which have tunable optical absorption and high carrier mobility) with organic materials (which are abundant with low cost, high flexibility and large-area scalability) to form thin-film heterojunctions, high-responsivity photodetectors could be predicted with fast response speed in a wide spectra region. In this review, we give a comprehensive summary of photodetectors based on two-dimensional materials and organic thin-film heterojunctions, which includes hybrid assisted enhanced devices, single-layer enhanced devices, vertical heterojunction devices and tunable vertical heterojunction devices. We also give a systematic classification and perspectives on the future development of these types of photodetectors.

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Optical characterization of defects in narrow-gap HgCdTe for infrared detector applications Fang-Yu Yue(越方禹), Su-Yu Ma(马骕驭), Jin Hong(洪进), Ping-Xiong Yang(杨平雄), Cheng-Bin Jing(敬承斌), Ye Chen(陈晔), Jun-Hao Chu(褚君浩) Chin. Phys. B, 2019, 28 (1):  017104.  DOI: 10.1088/1674-1056/28/1/017104 Abstract ( 1064 )   HTML   PDF (2339KB) ( 278 )   Narrow-gap Hg1-xCdxTe material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x≈ 0.3 are reviewed, including the defects and defect levels of intrinsic VHg and the extrinsic amphoteric arsenic (As) dopants, which can act as shallow/deep donors and acceptors. The influence of the defects on the determination of band-edge electronic structure is discussed when absorption or photoluminescence spectra are considered. The inconsistency between these two optical techniques is demonstrated and analyzed by taking into account the Fermi level position as a function of composition, doping level, conductivity type, and temperature. The defect level and its evolution, especially in As-doped HgCdTe, are presented. Our results provide a systematic understanding of the mechanisms and help for optimizing annealing conditions towards p-type As-activation, and eventually for fabricating high performance mid-infrared detectors.

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Review of gallium oxide based field-effect transistors and Schottky barrier diodes Zeng Liu(刘增), Pei-Gang Li(李培刚), Yu-Song Zhi(支钰崧), Xiao-Long Wang(王小龙), Xu-Long Chu(褚旭龙), Wei-Hua Tang(唐为华) Chin. Phys. B, 2019, 28 (1):  017105.  DOI: 10.1088/1674-1056/28/1/017105 Abstract ( 993 )   HTML   PDF (5647KB) ( 927 )   Gallium oxide (Ga2O3), a typical ultra wide bandgap semiconductor, with a bandgap of~4.9 eV, critical breakdown field of 8 MV/cm, and Baliga's figure of merit of 3444, is promising to be used in high-power and high-voltage devices. Recently, a keen interest in employing Ga2O3 in power devices has been aroused. Many researches have verified that Ga2O3 is an ideal candidate for fabricating power devices. In this review, we summarized the recent progress of field-effect transistors (FETs) and Schottky barrier diodes (SBDs) based on Ga2O3, which may provide a guideline for Ga2O3 to be preferably used in power devices fabrication.

TOPICAL REVIEW—Fundamental research under high magnetic fields

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Heavy fermions in high magnetic fields M Smidman, B Shen(沈斌), C Y Guo(郭春煜), L Jiao(焦琳), X Lu(路欣), H Q Yuan(袁辉球) Chin. Phys. B, 2019, 28 (1):  017106.  DOI: 10.1088/1674-1056/28/1/017106 Abstract ( 677 )   HTML   PDF (7769KB) ( 422 )   Heavy fermion materials are prototypical strongly correlated electron systems, where the strong electron–electron interactions lead to a wide range of novel phenomena and emergent phases of matter. Due to the low energy scales, the relative strengths of the Ruderman–Kittel–Kasuya–Yosida (RKKY) and Kondo interactions can often be readily tuned by non-thermal control parameters such as pressure, doping, or applied magnetic fields, which can give rise to quantum criticality and unconventional superconductivity. Here we provide a brief overview of research into heavy fermion materials in high magnetic fields, focussing on three main areas. Firstly we review the use of magnetic fields as a tuning parameter, and in particular the ability to realize different varieties of quantum critical behaviors. We then discuss the properties of heavy fermion superconductors in magnetic fields, where experiments in applied fields can reveal the nature of the order parameter, and induce new novel phenomena. Finally we report recent studies of topological Kondo systems, including topological Kondo insulators and Kondo–Weyl semimetals. Here experiments in magnetic fields can be used to probe the topologically non-trivial Fermi surface, as well as related field-induced phenomena such as the chiral anomaly and topological Hall effect.

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

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Exploration of the structural and optical properties of a red-emitting phosphor K2TiF6:Mn4+ Xi-Long Dou(豆喜龙), Xiao-Yu Kuang(邝小渝), Xin-Xin Xia(夏欣欣), Meng Ju(巨濛) Chin. Phys. B, 2019, 28 (1):  017107.  DOI: 10.1088/1674-1056/28/1/017107 Abstract ( 548 )   HTML   PDF (1445KB) ( 409 )   The exploration of the appropriate red phosphor with good luminescence properties is an important issue in the development of current white light-emitting diode (WLED) devices. Transition metal Mn-doped compounds are fascinating luminescent materials. Herein, we performed a systematic theoretical study of the microstructure and optical properties of K2TiF6:Mn4+ using the CALYPSO structure search method in combination with first-principles calculations. We uncovered a novel structure of K2TiF6:Mn4+ with space group P-3m1 symmetry, where the impurity Mn4+ ions are accurately located at the center of the MnF6 octahedra. Based on our developed complete energy matrix diagonalization (CEMD) method, we calculated transition lines for 2Eg→4A2, 4A2→4T2, and 4A2→4T2 at 642 nm, 471 nm, and 352 nm, respectively, which are in good agreement with the available experimental data. More remarkably, we also found another transition (4A2→2T2) that lies at 380 nm, which should be a promising candidate for laser action.

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Inverse spin Hall effect in ITO/YIG exited by spin pumping and spin Seebeck experiments Kejian Zhu(朱科建), Weijian Lin(林伟坚), Yangtao Su(苏仰涛), Haibin Shi(石海滨), Yang Meng(孟洋), Hongwu Zhao(赵宏武) Chin. Phys. B, 2019, 28 (1):  017201.  DOI: 10.1088/1674-1056/28/1/017201 Abstract ( 713 )   HTML   PDF (1197KB) ( 232 )   Spin currents, which are excited in indium tin oxide (ITO)/yttrium iron garnet (YIG) by the methods of spin pumping and spin Seebeck effect, are investigated through the inverse spin Hall effect (ISHE). It is demonstrated that the ISHE voltage can be generated in ITO by spin pumping under both in-plane and out-of-plane magnetization configurations. Moreover, it is observed that the enhancement of spin Hall angle and interfacial spin mixing conductance can be achieved by an appropriate annealing process. However, the ISHE voltage is hardly seen in the presence of a longitudinal temperature gradient. The absence of the longitudinal spin Seebeck effect can be ascribed to the almost equal thermal conductivity of ITO and YIG and specific interface structure, or to the large negative temperature dependent spin mixing conductance.

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Semi-analytic study on the conductance of a lengthy armchair honeycomb nanoribbon including vacancies, defects, or impurities Fateme Nadri, Mohammad Mardaani, Hassan Rabani Chin. Phys. B, 2019, 28 (1):  017202.  DOI: 10.1088/1674-1056/28/1/017202 Abstract ( 581 )   HTML   PDF (514KB) ( 143 )   We present a semi-analytic method to study the electronic conductance of a lengthy armchair honeycomb nanoribbon in the presence of vacancies, defects, or impurities located at a small part of it. For this purpose, we employ the Green's function technique within the nearest neighbor tight-binding approach. We first convert the Hamiltonian of an ideal semi-infinite nanoribbon to the Hamiltonian of some independent polyacetylene-like chains. Then, we derive an exact formula for the self-energy of the perturbed part due to the existence of ideal parts. The method gives a fully analytical formalism for some cases such as an infinite ideal nanoribbon and the one including linear symmetric defects. We calculate the transmission coefficient for some different configurations of a nanoribbon with special width including a vacancy, edge geometrical defects, and two electrical impurities.

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Current diffusion and efficiency droop in vertical light emitting diodes R Q Wan(万荣桥), T Li(李滔), Z Q Liu(刘志强), X Y Yi(伊晓燕), J X Wang(王军喜), J H Li(李军辉), W H Zhu(朱文辉), J M Li(李晋闽), L C Wang(汪炼成) Chin. Phys. B, 2019, 28 (1):  017203.  DOI: 10.1088/1674-1056/28/1/017203 Abstract ( 624 )   HTML   PDF (778KB) ( 144 )   Current diffusion is an old issue, nevertheless, the relationship between the current diffusion and the efficiency of light emitting diodes (LEDs) needs to be further quantitatively clarified. By incorporating current crowding effect (CCE) into the conventional ABC model, we have theoretically and directly correlated the current diffusion and the internal quantum efficiency (IQE), light extraction efficiency (LEE), and external quantum efficiency (EQE) droop of the lateral LEDs. However, questions still exist for the vertical LEDs (V-LEDs). Here firstly the current diffusion length Ls(I) and Ls(Ⅱ) have been clarified. Based on this, the influence of CCE on the EQE, IQE, and LEE of V-LEDs were investigated. Specifically to our V-LEDs with moderate series resistivity, Ls(Ⅲ) was developed by combining Ls(I) and Ls(Ⅱ), and the CCE effect on the performance of V-LEDs was investigated. The wall-plug efficiency (WPE) of V-LEDs ware investigated finally. Our works provide a deep understanding of the current diffusion status and the correlated efficiency droop in V-LEDs, thus would benefit the V-LEDs' chip design and further efficiency improvement.

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Generation of valley pump currents in silicene John Tombe Jada Marcellino, Mei-Juan Wang(王美娟), Sa-Ke Wang(汪萨克) Chin. Phys. B, 2019, 28 (1):  017204.  DOI: 10.1088/1674-1056/28/1/017204 Abstract ( 244117 )   HTML   PDF (433KB) ( 241925 )   We propose a workable scheme for generating a bulk valley pump current in a silicene-based device which consists of two pumping regions characterized by time-dependent strain and staggered potentials, respectively. In a one-dimension model, we show that a pure valley current can be generated, in which the two valley currents have the same magnitude but flow in opposite directions. Besides, the pumped valley current is quantized and maximized when the Fermi energy of the system locates in the bandgap opened by the two pumping potentials. Furthermore, the valley current can be finely controlled by tuning the device parameters. Our results are useful for the development of valleytronic devices based on two-dimensional materials.

RAPID COMMUNICATION

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Pressure-mediated contact quality improvement between monolayer MoS2 and graphite Mengzhou Liao(廖梦舟), Luojun Du(杜罗军), Tingting Zhang(张婷婷), Lin Gu(谷林), Yugui Yao(姚裕贵), Rong Yang(杨蓉), Dongxia Shi(时东霞), Guangyu Zhang(张广宇) Chin. Phys. B, 2019, 28 (1):  017301.  DOI: 10.1088/1674-1056/28/1/017301 Abstract ( 854 )   HTML   PDF (1311KB) ( 383 )   Two-dimensional (2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS2 as the most typical 2D semiconductors has great application potential in thin film transistors, photodetector, hydrogen evolution reaction, memory device, etc. However, the performance of MoS2 devices is limited by the contact resistance and the improvement of its contact quality is important. In this work, we report the experimental investigation of pressure-enhanced contact quality between monolayer MoS2 and graphite by conductive atom force microscope (C-AFM). It was found that at high pressure, the contact quality between graphite and MoS2 is significantly improved. This pressure-mediated contact quality improvement between MoS2 and graphite comes from the enhanced charge transfer between MoS2 and graphite when MoS2 is stretched. Our results provide a new way to enhance the contact quality between MoS2 and graphite for further applications.

TOPICAL REVIEW—Photodetector: materials, physics, and applications

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Room-temperature infrared photodetectors with hybrid structure based on two-dimensional materials Tiande Liu(刘天德), Lei Tong(童磊), Xinyu Huang(黄鑫宇), Lei Ye(叶镭) Chin. Phys. B, 2019, 28 (1):  017302.  DOI: 10.1088/1674-1056/28/1/017302 Abstract ( 681 )   HTML   PDF (8629KB) ( 468 )   Two-dimensional (2D) materials, such as graphene, transition metal dichalcogenides (TMDs), black phosphorus (BP), and related derivatives, have attracted great attention due to their advantages of flexibility, strong light-matter interaction, broadband absorption, and high carrier mobility, and have become a powerful contender for next-generation infrared photodetectors. However, since the thickness of 2D materials is on the order of nanometers, the absorption of 2D materials is very weak, which limits the detection performance of 2D materials-based infrared photodetectors. In order to solve this problem, scientific researchers have tried to use optimized device structures to combine with 2D materials for improving the performance of infrared photodetectors. In this review, we review the progress of room-temperature infrared photodetectors with hybrid structure based on 2D materials in recent years, focusing mainly on 2D-nD (n=0, 1, 2) heterostructures, the integration between 2D materials and on-chip or plasmonic structure. Finally, we summarize the current challenges and point out the future development direction.

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

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Investigation and active suppression of self-heating induced degradation in amorphous InGaZnO thin film transistors Dong Zhang(张东), Chenfei Wu(武辰飞), Weizong Xu(徐尉宗), Fangfang Ren(任芳芳), Dong Zhou(周东), Peng Yu(于芃), Rong Zhang(张荣), Youdou Zheng(郑有炓), Hai Lu(陆海) Chin. Phys. B, 2019, 28 (1):  017303.  DOI: 10.1088/1674-1056/28/1/017303 Abstract ( 808 )   HTML   PDF (528KB) ( 230 )   Self-heating effect in amorphous InGaZnO thin-film transistors remains a critical issue that degrades device performance and stability, hindering their wider applications. In this work, pulsed current-voltage analysis has been applied to explore the physics origin of self-heating induced degradation, where Joule heat is shortly accumulated by drain current and dissipated in repeated time cycles as a function of gate bias. Enhanced positive threshold voltage shift is observed at reduced heat dissipation time, higher drain current, and increased gate width. A physical picture of Joule heating assisted charge trapping process has been proposed and then verified with pulsed negative gate bias stressing scheme, which could evidently counteract the self-heating effect through the electric-field assisted detrapping process. As a result, this pulsed gate bias scheme with negative quiescent voltage could be used as a possible way to actively suppress self-heating related device degradation.

RAPID COMMUNICATION

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Electronic synapses based on ultrathin quasi-two-dimensional gallium oxide memristor Hot! Shuopei Wang(王硕培), Congli He(何聪丽), Jian Tang(汤建), Rong Yang(杨蓉), Dongxia Shi(时东霞), Guangyu Zhang(张广宇) Chin. Phys. B, 2019, 28 (1):  017304.  DOI: 10.1088/1674-1056/28/1/017304 Abstract ( 1326 )   HTML   PDF (1465KB) ( 462 )   Synapse emulation is very important for realizing neuromorphic computing, which could overcome the energy and throughput limitations of today's computing architectures. Memristors have been extensively studied for using in nonvolatile memory storage and neuromorphic computing. In this paper, we report the fabrication of vertical sandwiched memristor device using ultrathin quasi-two-dimensional gallium oxide produced by squeegee method. The as-fabricated two-terminal memristor device exhibited the essential functions of biological synapses, such as depression and potentiation of synaptic weight, transition from short time memory to long time memory, spike-timing-dependent plasticity, and spike-rate-dependent plasticity. The synaptic weight of the memristor could be tuned by the applied voltage pulse, number, width, and frequency. We believe that the injection of the top Ag cations should play a significant role for the memristor phenomenon. The ultrathin of medium layer represents an advance to integration in vertical direction for future applications and our results provide an alternative way to fabricate synaptic devices.

SPECIAL TOPIC—Photodetector: Materials, physics, and applications

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Synthesis of free-standing Ga2O3 films for flexible devices by water etching of Sr3Al2O6 sacrificial layers Xia Wang(王霞), Zhen-Ping Wu(吴真平), Wei Cui(崔尉), Yu-Song Zhi(支钰崧), Zhi-Peng Li(李志鹏), Pei-Gang Li(李培刚), Dao-You Guo(郭道友), Wei-Hua Tang(唐为华) Chin. Phys. B, 2019, 28 (1):  017305.  DOI: 10.1088/1674-1056/28/1/017305 Abstract ( 677 )   HTML   PDF (2459KB) ( 311 )   Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga2O3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga2O3 thin films using the water-soluble perovskite Sr3Al2O6 as a sacrificial buffer layer. The obtained Ga2O3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga2O3 solar-blind UV photodetector was fabricated by transferring the free-standing Ga2O3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga2O3 photodetector were not sensitive to bending of the device. The free-standing Ga2O3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.

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

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Synthesis, physical properties, and annealing investigation of new layered Bi-chalcogenide LaOBiHgS3 Yi Yu(于一), Chunchang Wang(汪春昌), Liang Li(李亮), Qiuju Li(李秋菊), Chao Cheng(程超), Shuting Wang(王舒婷), Changjin Zhang(张昌锦) Chin. Phys. B, 2019, 28 (1):  017401.  DOI: 10.1088/1674-1056/28/1/017401 Abstract ( 711 )   HTML   PDF (488KB) ( 165 )   The transport and thermoelectric properties together with annealing of the new layered Bi-chalcogenide LaOBiHgS3 are studied. On the transport part, the insulating behavior of the as-grown sample is evidently depressed by post annealing. A hump-like abnormality appears around 170 K. The thermoelectric performance of the sample is observably improved by the annealing, mainly because of the enhanced electrical conductance. The present results suggest that the physical properties of LaOBiHgS3 are sensitive to post annealing and the possible micro adjustments that follow, indicating the layered Bi-chalcogenide family to be an ideal platform for designing novel functional materials.

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Quantum critical duality in two-dimensional Dirac semimetals Jiang Zhou(周江), Ya-Jie Wu(吴亚杰), Su-Peng Kou(寇谡鹏) Chin. Phys. B, 2019, 28 (1):  017402.  DOI: 10.1088/1674-1056/28/1/017402 Abstract ( 845 )   HTML   PDF (432KB) ( 206 )   Quantum criticality is closely related to the existence of two phases with unrelated symmetry breaking. In this paper, we study Néel and Kekulé valence bond state (VBS) quantum criticality in Dirac semimetals with four-fermion interactions. Our results show that all possible dynamical masses yield the same critical coupling, which exhibits the phenomenon that all possible phases meet at a multicritical point (e.g., a tricritical point for the Néel, Kekulé-VBS and semimetallic phases). In terms of the well-established Wess-Zumino-Witten field theory, we investigate the typical criticality for the transition between Néel and Kekulé-VBS phases, and the compatible Néel-Kekulé-VBS mass matrices imply the existence of a non-Landau transition between the Néel and Kekulé-VBS phases. We show the existence of mutual duality in the defect-driven Néel-Kekulé-VBS transition near the non-Landau critical point and find that this mutual duality results from the presence of a mutual Chern-Simons term. We also study the mutual duality based on dual topological excitations.

TOPICAL REVIEW—Magnetism, magnetic materials, and interdisciplinary research

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Sm–Co high-temperature permanent magnet materials Shiqiang Liu(刘世强) Chin. Phys. B, 2019, 28 (1):  017501.  DOI: 10.1088/1674-1056/28/1/017501 Abstract ( 1115 )   HTML   PDF (9994KB) ( 636 )   Permanent magnets capable of reliably operating at high temperatures up to ~450℃ are required in advanced power systems for future aircrafts, vehicles, and ships. Those operating temperatures are far beyond the capability of Nd– Fe–B magnets. Possessing high Curie temperature, Sm–Co based magnets are still very important because of their hightemperature capability, excellent thermal stability, and better corrosion resistance. The extensive research performed around the year 2000 resulted in a new class of Sm2(Co, Fe, Cu, Zr)17-type magnets capable of operating at high temperatures up to 550℃. This paper gives a systematic review of the development of Sm–Co permanent magnets, from the crystal structures and phase diagrams to the intrinsic magnetic properties. An emphasis is placed on Sm2(Co, Fe, Cu, Zr)17-type magnets for operation at temperatures from 300℃ to 550℃. The thermal stability issues, including instantaneous temperature coefficients of magnetic properties, are discussed in detail. The significance of nanograin structure, nanocrystalline, and nanocomposite Sm–Co magnet materials, and prospects of future rare-earth permanent magnets are also given.

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

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Harvesting base vibration energy by a piezoelectric inverted beam with pendulum Jia-Nan Pan(潘家楠), Wei-Yang Qin(秦卫阳), Wang-Zheng Deng(邓王蒸), Hong-Lei Zhou(周红磊) Chin. Phys. B, 2019, 28 (1):  017701.  DOI: 10.1088/1674-1056/28/1/017701 Abstract ( 847 )   HTML   PDF (3539KB) ( 206 )   We proposed a two-degrees-of-freedom inverted piezoelectric beam with pendulum to promote the performance of vibration energy harvesting. This configuration is composed of an inverted elastic beam and a pendulum attached to its free end. The electromechanical equations governing the nonlinear system were derived. The harmonic balance method (HBM) is applied to solve the equation and the results prove that there exists a 1:3 super-harmonic resonance. The simulation results show that owing to the particular nonlinearity, there appears a special bending effect in the amplitude-frequency response, i.e., bending right for the first natural frequency and left for the second natural frequency, which is beneficial for harvesting vibration energy. The HBM results are verified by the entity simulations. Furthermore, over a relatively wide range of power spectral density, it could reach a dense jumping and give a dense high pulse voltage.

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Light absorption coefficients of ionic liquids under electric field Ji Zhou(周吉), Shi-Kui Dong(董士奎), Zhi-Hong He(贺志宏), Ju-Lius Caesar Puoza, Yan-Hu Zhang(张彦虎) Chin. Phys. B, 2019, 28 (1):  017801.  DOI: 10.1088/1674-1056/28/1/017801 Abstract ( 669 )   HTML   PDF (8211KB) ( 163 )   Ionic liquids have attracted a lot of research attention for their applications in novel optoelectronic structures and devices as an optical means of regulating electricity. Although the electro-optic effect of ionic liquids is mentioned in some literature, quantitative testing and analysis are hardly found in light absorption coefficients of ionic liquids under an electric field. In the present study, an experimental apparatus is designed to measure the absorption coefficients of ionic liquids under different electric fields. Five groups of imidazole ionic liquids are experimentally investigated and an inversion is performed to determine the spectral absorption coefficients of the imidazole ionic liquids under the electric fields. Different intensities with multiple interface refractions and reflections are also considered, and the various measurement errors are analyzed through uncertainties propagation analysis. Spectral absorptions of ionic liquids from 300 nm to 2500 nm are obtained and the absorption coefficients are retrieved. It is found that the absorption behavior of ionic liquids changes in some frequency bands under an applied electric field. The experimental results show that the absorption coefficient of the ionic liquid increases with the voltage increasing at 1520 nm and 1920 nm. The change rate is affected by the types of anions and cations in the ionic liquid and the diffusion rate of the ions therein. This study provides illustrations for the ionic liquid-based electro-optical regulation in terms of physical property parameters and the testing technique.

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First-principles study on optic-electronic properties of doped formamidinium lead iodide perovskite Xin-Feng Diao(刁心峰), Yan-Lin Tang(唐延林), Quan Xie(谢泉) Chin. Phys. B, 2019, 28 (1):  017802.  DOI: 10.1088/1674-1056/28/1/017802 Abstract ( 733 )   HTML   PDF (1582KB) ( 473 )   We have discussed the materials of solar cell based on hybrid organic-inorganic halide perovskites with formamidinium (NH2CH=NH2+ or FA) lead iodide. Firstly, we build the structure of formamidinium lead iodide (FAPbI3) by using the material studio. By using the first-principles calculations, the energy band structure, density of states (DOS), and partial DOS (PDOS) of the hydrazine-iodide lead halide are obtained. Then, we theoretically analyze a design scheme for perovskite solar cell materials, published in[Science 354, 861 (2016)], with the photoelectric conversion efficiency that can reach 20.3%. Also, we use non-toxic elements to replace lead in FAPbI3 without affecting its photoelectric conversion efficiency. Here in this work, we explore the energy band structure, lattice constant, light absorption efficiency, etc. After the Ca, Zn, Ge Sr, Sn, and Ta atoms replacing lead (Pb) and through comparing the spectral distributions of the solar spectrum, it can be found that FAGeI3, FASnI3, and FAZnI3 have better absorbance characteristics in the solar spectrum range. If the band gap structure is taken into account, FAGeI3 will become an ideal material to replace FAPbI3, although its performance is slightly lower than that of FAPbI3. The toxicity of Pb is taken into account, and the Ge element can be used as a substitute element for Pb. Furthermore, we explore one of the perovskite materials, i.e., FA0.75Cs0.25Sn0.25Ge0.75I3 whose photovoltaic properties are close to those of FA0.75Cs0.25Sn0.5Pb0.5I3, but the former does not contain toxic atoms. Our results pave the way for further investigating the applications of these materials in relevant technologies.

TOPICAL REVIEW—Photodetector: materials, physics, and applications

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Photodetectors based on inorganic halide perovskites: Materials and devices Ying Li(李营), Zhi-Feng Shi(史志锋), Xin-Jian Li(李新建), Chong-Xin Shan(单崇新) Chin. Phys. B, 2019, 28 (1):  017803.  DOI: 10.1088/1674-1056/28/1/017803 Abstract ( 829 )   HTML   PDF (3520KB) ( 691 )   The newly emerging metal halide perovskites have attracted considerable attention due to their exceptional optoelectronic properties. This upsurge was initially driven when the power conversion efficiency of perovskite-based photovoltaic devices exceeded 23%. Due to their optoelectronic properties, perovskite materials have also been used in light-emitting diodes, photodetectors, lasers, and memory devices. This study comprehensively discusses the recent progress of all-inorganic perovskite-based photodetectors, focusing on their structures, morphologies of their constituent materials, and diverse device architectures that improve the performance metrics of these photodetectors. A brief outlook, highlighting the main existing problems, possible solutions to these problems, and future development directions, is also provided herein.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Criteria for Beverloo's scaling law Sheng Zhang(张晟), Ping Lin(林平), Guanghui Yang(杨光辉), Jiang-Feng Wan(万江锋), Yuan Tian(田园), Lei Yang(杨磊) Chin. Phys. B, 2019, 28 (1):  018101.  DOI: 10.1088/1674-1056/28/1/018101 Abstract ( 781 )   HTML   PDF (2620KB) ( 170 )   Beverloo's scaling law can describe the flow rate of grains discharging from hoppers. In this paper, we show that the Beverloo's scaling law is valid for varying material parameters. The flow rates from a hopper with different hopper and orifice sizes (D, D0) are studied by running large-scale simulations. When the hopper size is fixed, the numerical results show that Beverloo's law is valid even if the orifice diameter is very large and then the criteria for this law are discussed. To eliminate the effect of walls, it is found that the criteria can be suggested as D-D0 ≥ 40d or D/D0 ≥ 2. Interestingly, it is found that there is still a scaling relation between the flow rate and orifice diameter if D/D0 is fixed and less than 2. When the orifice diameter is close to the hopper size, the velocity field changes and the vertical velocities of grains above the free fall region are much larger. Then, the free fall arch assumption is invalid and Beverloo's law is inapplicable.

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High-performance InAlGaN/GaN enhancement-mode MOS-HEMTs grown by pulsed metal organic chemical vapor deposition Ya-Chao Zhang(张雅超), Zhi-Zhe Wang(王之哲), Rui Guo(郭蕊), Ge Liu(刘鸽), Wei-Min Bao(包为民), Jin-Cheng Zhang(张进成), Yue Hao(郝跃) Chin. Phys. B, 2019, 28 (1):  018102.  DOI: 10.1088/1674-1056/28/1/018102 Abstract ( 655 )   HTML   PDF (1276KB) ( 171 )   Pulsed metal organic chemical vapor deposition was employed to grow nearly polarization matched InAlGaN/GaN heterostructures. A relatively low sheet carrier density of 1.8×1012 cm-2, together with a high electron mobility of 1229.5 cm2/V·s, was obtained for the prepared heterostructures. The surface morphology of the heterostructures was also significantly improved, i.e., with a root mean square roughness of 0.29 nm in a 2 μm×2 μm scan area. In addition to the improved properties, the enhancement-mode metal–oxide–semiconductor high electron mobility transistors (MOSHEMTs) processed on the heterostructures not only exhibited a high threshold voltage (VTH) of 3.1 V, but also demonstrated a significantly enhanced drain output current density of 669 mA/mm. These values probably represent the largest values obtained from the InAlGaN based enhancement-mode devices to the best of our knowledge. This study strongly indicates that the InAlGaN/GaN heterostructures grown by pulsed metal organic chemical vapor deposition could be promising for the applications of novel nitride-based electronic devices.

TOPICAL REVIEW—Photodetector: materials, physics, and applications

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A review on MBE-grown HgCdSe infrared materials on GaSb (211)B substrates Z K Zhang, W W Pan, J L Liu, W Lei Chin. Phys. B, 2019, 28 (1):  018103.  DOI: 10.1088/1674-1056/28/1/018103 Abstract ( 923 )   HTML   PDF (5470KB) ( 345 )   We review our recent efforts on developing HgCdSe infrared materials on GaSb substrates via molecular beam epitaxy (MBE) for fabricating next generation infrared detectors with features of lower production cost and larger focal plane array format size. In order to achieve high-quality HgCdSe epilayers, ZnTe buffer layers are grown before growing HgCdSe, and the study of misfit strain in ZnTe buffer layers shows that the thickness of ZnTe buffer layer needs to be below 300 nm in order to minimize the generation of misfit dislocations. The cut-off wavelength/alloy composition of HgCdSe materials can be varied in a wide range by varying the ratio of Se/Cd beam equivalent pressure during the HgCdSe growth. Growth temperature presents significant impact on the material quality of HgCdSe, and lower growth temperature leads to higher material quality for HgCdSe. Typically, long-wave infrared HgCdSe (x = 0.18, cut-off wavelength of 10.4 μm at 80 K) presents an electron mobility as high as 1.3×105 cm2·V-1·s-1, a background electron concentration as low as 1.6×1016 cm-3, and a minority carrier lifetime as long as 2.2 μs. These values of electron mobility and minority carrier lifetime represent a significant improvement on previous studies of MBE-grown HgCdSe reported in the open literatures, and are comparable to those of counterpart HgCdTe materials grown on lattice-matched CdZnTe substrates. These results indicate that HgCdSe grown at the University of Western Australia, especially long-wave infrared can meet the basic material quality requirements for making high performance infrared detectors although further effort is required to control the background electron concentration to below 1015 cm-3. More importantly, even higher quality HgCdSe materials on GaSb are expected by further optimizing the growth conditions, using higher purity Se source material, and implementing postgrowth thermal annealing and defect/impurity gettering/filtering. Our results demonstrate the great potential of HgCdSe infrared materials grown on GaSb substrates for fabricating next generation infrared detectors with features of lower cost and larger array format size.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Influence of wall friction on granular column Yang-Yang Yang(杨阳阳), Sheng Zhang(张晟), Ping Lin(林平), Jiang-Feng Wan(万江锋), Lei Yang(杨磊), Shurong Ding(丁淑蓉) Chin. Phys. B, 2019, 28 (1):  018104.  DOI: 10.1088/1674-1056/28/1/018104 Abstract ( 940 )   HTML   PDF (947KB) ( 168 )   Granular packings under gravity in frictional and frictionless silos were simulated and the influence of the wall friction on the normal force distribution was investigated. Although there is an obvious Janssen effect in frictional silos, only a slight influence on the geometry of packing was found. The law of normal force distribution is different for frictional and frictionless walls, which is related to the pressure profile. A modified formula with consideration of the pressure profile was well fitted to the simulation results.

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Exploring the effect of aggregation-induced emission on the excited state intramolecular proton transfer for a bis-imine derivative by quantum mechanics and our own n-layered integrated molecular orbital and molecular mechanics calculations Huifang Zhao(赵慧芳), Chaofan Sun(孙朝范), Xiaochun Liu(刘晓春), Hang Yin(尹航), Ying Shi(石英) Chin. Phys. B, 2019, 28 (1):  018201.  DOI: 10.1088/1674-1056/28/1/018201 Abstract ( 896 )   HTML   PDF (1598KB) ( 182 )   We theoretically investigate the excited state intramolecular proton transfer (ESIPT) behavior of the novel fluorophore bis-imine derivative molecule HNP which was designed based on the intersection of 1-(hydrazonomethyl)-naphthalene-2-ol and 1-pyrenecarboxaldehyde. Especially, the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods for HNP monomer are introduced. Moreover, the “our own n-layered integrated molecular orbital and molecular mechanics” (ONIOM) method (TDDFT:universal force field (UFF)) is used to reveal the aggregation-induced emission (AIE) effect on the ESIPT process for HNP in crystal. Our results confirm that the ESIPT process happens upon the photoexcitation for the HNP monomer and HNP in crystal, which is distinctly monitored by the optimized geometric structures and the potential energy curves. In addition, the results of potential energy curves reveal that the ESIPT process in HNP will be promoted by the AIE effect. Furthermore, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) for the HNP monomer and HNP in crystal have been calculated. The calculation demonstrates that the electron density decrease of proton donor caused by excitation promotes the ESIPT process. In addition, we find that the variation of atomic dipole moment corrected Hirshfeld population (ADCH) charge for proton acceptor induced by the AIE effect facilitates the ESIPT process. The results will be expected to deepen the understanding of ESIPT dynamics for luminophore under the AIE effect and provide insight into future design of high-efficient AIE compounds.

TOPICAL REVIEW—Photodetector: materials, physics, and applications

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Review of deep ultraviolet photodetector based on gallium oxide Yuan Qin(覃愿), Shibing Long(龙世兵), Hang Dong(董航), Qiming He(何启鸣), Guangzhong Jian(菅光忠), Ying Zhang(张颖), Xiaohu Hou(侯小虎), Pengju Tan(谭鹏举), Zhongfang Zhang(张中方), Hangbing Lv(吕杭炳), Qi Liu(刘琦), Ming Liu(刘明) Chin. Phys. B, 2019, 28 (1):  018501.  DOI: 10.1088/1674-1056/28/1/018501 Abstract ( 1157 )   HTML   PDF (10717KB) ( 1097 )   Ultraviolet (UV) photodetectors (PDs) have drawn great attention in recent years due to their potential application in civil and military fields. Because of its ultrawide bandgap, low cost, strong radiation hardness, and high thermal and chemical stability with high visible-light transparency, Ga2O3 is regarded as the most promising candidate for UV detection. Furthermore, the bandgap of Ga2O3 is as high as 4.7-4.9 eV, directly corresponding to the solar-blind UV detection band with wavelength less than 280 nm. There is no need of doping in Ga2O3 to tune its bandgap, compared to AlGaN, MgZnO, etc, thereby avoiding alloy composition fluctuations and phase separation. At present, solar-blind Ga2O3 photodetectors based on single crystal or amorphous Ga2O3 are mainly focused on metal-semiconductor-metal and Schottky photodiodes. In this work, the recent achievements of Ga2O3 photodetectors are systematically reviewed. The characteristics and performances of different photodetector structures based on single crystal Ga2O3 and amorphous Ga2O3 thin film are analyzed and compared. Finally, the prospects of Ga2O3 UV photodetectors are forecast.

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Metal halide perovskite photodetectors: Material featuresand device engineering Ye Wang(王烨), Meng-Lei Gao(高孟磊), Jin-Liang Wu(吴金良), Xing-Wang Zhang(张兴旺) Chin. Phys. B, 2019, 28 (1):  018502.  DOI: 10.1088/1674-1056/28/1/018502 Abstract ( 1005 )   HTML   PDF (4180KB) ( 474 )   In recent years, the rapid progress of metal halide perovskite solar cells has been witnessed by the rocketing power conversion efficiency. In addition, perovskites have opened up a great opportunity for high performance photodetectors (PDs), due to their attractive optical and electrical properties. This review summarizes the latest progress of perovskite-based PDs, aiming to give a comprehensive understanding of the material design and device engineering in perovskite PDs. To begin with, the performance parameters and device configurations of perovskite PDs are introduced, which are the basis for the next discussion. Next, various PDs based on perovskites in different morphologies are discussed from two aspects:the preparation method, and device performance. Then, several device engineering strategies to enhance the performance of perovskite-based PDs are highlighted, followed by the introduction of flexible and narrow-band perovskite PDs. Finally, key issues and major challenges of perovskite PDs that need to be addressed in the future are outlined.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Efficiency enhancement of ultraviolet light-emitting diodes with segmentally graded p-type AlGaN layer Lin-Yuan Wang(王林媛), Wei-Dong Song(宋伟东), Wen-Xiao Hu(胡文晓), Guang Li(李光), Xing-Jun Luo(罗幸君), Hu Wang(汪虎), Jia-Kai Xiao(肖稼凯), Jia-Qi Guo(郭佳琦), Xing-Fu Wang(王幸福), Rui Hao(郝锐), Han-Xiang Yi(易翰翔), Qi-Bao Wu(吴启保), Shu-Ti Li(李述体) Chin. Phys. B, 2019, 28 (1):  018503.  DOI: 10.1088/1674-1056/28/1/018503 Abstract ( 961 )   HTML   PDF (746KB) ( 184 )   AlGaN-based ultraviolet light-emitting diodes (UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency. The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-AlxGa1-xN has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-AlxGa1-xN, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.

SPECIAL TOPIC—Photodetector: Materials, physics, and applications

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Preparation of Ga2O3 thin film solar-blind photodetectors based on mixed-phase structure by pulsed laser deposition Y M Lu(吕有明), C Li(李超), X H Chen(陈相和), S Han(韩瞬), P J Cao(曹培江), F Jia(贾芳), Y X Zeng(曾玉祥), X K Liu(刘新科), W Y Xu(许望颖), W J Liu(柳文军), D L Zhu(朱德亮) Chin. Phys. B, 2019, 28 (1):  018504.  DOI: 10.1088/1674-1056/28/1/018504 Abstract ( 1010 )   HTML   PDF (1539KB) ( 343 )   Gallium oxide (Ga2O3) thin films were deposited on a-Al2O3 (1120) substrates by pulsed laser deposition (PLD) with different oxygen pressures at 650℃. By reducing the oxygen pressure, mixed-phase Ga2O3 films with α and β phases can be obtained, and on the basis of this, mixed-phase Ga2O3 thin film solar-blind photodetectors (SBPDs) were prepared. Comparing the responsivities of the mixed-phase Ga2O3 SBPDs and the single β-Ga2O3 SBPDs at a bias voltage of 25 V, it is found that the former has a maximum responsivity of approximately 12 A/W, which is approximately two orders of magnitude larger than that of the latter. This result shows that the mixed-phase structure of Ga2O3 thin films can be used to prepare high-responsivity SBPDs. Moreover, the cause of this phenomenon was investigated, which will provide a feasible way to improve the responsivity of Ga2O3 thin film SBPDs.

INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

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Optimization of ambipolar current and analog/RF performance for T-shaped tunnel field-effect transistor with gate dielectric spacer Ru Han(韩茹), Hai-Chao Zhang(张海潮), Dang-Hui Wang(王党辉), Cui Li(李翠) Chin. Phys. B, 2019, 28 (1):  018505.  DOI: 10.1088/1674-1056/28/1/018505 Abstract ( 924 )   HTML   PDF (792KB) ( 175 )   A new T-shaped tunnel field-effect transistor (TTFET) with gate dielectric spacer (GDS) structure is proposed in this paper. To further studied the effects of GDS structure on the TTFET, detailed device characteristics such as current-voltage relationships, energy band diagrams, band-to-band tunneling (BTBT) rate and the magnitude of the electric field are investigated by using TCAD simulation. It is found that compared with conventional TTFET and TTFET with gate-drain overlap (GDO) structure, GDS-TTFET not only has the minimum ambipolar current but also can suppress the ambipolar current under a more extensive bias range. Furthermore, the analog/RF performances of GDS-TTFET are also investigated in terms of transconductance, gate-source capacitance, gate-drain capacitance, cutoff frequency, and gain bandwidth production. By inserting a low-κ spacer layer between the gate electrode and the gate dielectric, the GDS structure can effectively reduce parasitic capacitances between the gate and the source/drain, which leads to better performance in term of cutoff frequency and gain bandwidth production. Finally, the thickness of the gate dielectric spacer is optimized for better ambipolar current suppression and improved analog/RF performance.

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Entrainment range affected by the heterogeneity in the amplitude relaxation rate of suprachiasmatic nucleus neurons Chang-Gui Gu(顾长贵), Ping Wang(王萍), Hui-Jie Yang(杨会杰) Chin. Phys. B, 2019, 28 (1):  018701.  DOI: 10.1088/1674-1056/28/1/018701 Abstract ( 671 )   HTML   PDF (1634KB) ( 148 )   Adaption of circadian rhythms in behavioral and physiological activities to the external light-dark cycle is achieved through the main clock, i.e., the suprachiasmatic nucleus (SCN) of the brain in mammals. It has been found that the SCN neurons differ in the amplitude relaxation rate, which represents the rigidity of the neurons to the external amplitude disturbance. Thus far, the appearance of that difference has not been explained. In the present study, an alternative explanation based on the Poincaré model is given which takes into account the effect of the difference in the entrainment range of the SCN. Both our simulation results and theoretical analyses show that the largest entrainment range is obtained with suitable difference in the case that only a part of SCN neurons are sensitive to the light information. Our findings may give an alternative explanation for the appearance of that difference (heterogeneity) and shed light on the effects of the heterogeneity in the neuronal properties on the collective behaviors of the SCN neurons.