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Chin. Phys. B  
  Chin. Phys. B--2018, Vol.27, No.7
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Multi-soliton solutions for the coupled modified nonlinear Schrödinger equations via Riemann-Hilbert approach

Zhou-Zheng Kang, Tie-Cheng Xia, Xi Ma
Chin. Phys. B 2018, 27 (7): 070201;  doi: 10.1088/1674-1056/27/7/070201
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The coupled modified nonlinear Schrödinger equations are under investigation in this work. Starting from analyzing the spectral problem of the Lax pair, a Riemann-Hilbert problem for the coupled modified nonlinear Schrödinger equations is formulated. And then, through solving the obtained Riemann-Hilbert problem under the conditions of irregularity and reflectionless case, N-soliton solutions for the equations are presented. Furthermore, the localized structures and dynamic behaviors of the one-soliton solution are shown graphically.

A macroscopic traffic model based on weather conditions

Zawar H. Khan, Syed Abid Ali Shah, T. Aaron Gulliver
Chin. Phys. B 2018, 27 (7): 070202;  doi: 10.1088/1674-1056/27/7/070202
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A traffic model based on the road surface conditions during adverse weather is presented. The surface of a road is affected by snow, compacted snow, and ice, which affects the traffic behavior. In this paper, a new macroscopic traffic flow model based on the transition velocity distribution is proposed which characterizes traffic alignment under adverse weather conditions. Two examples are considered to illustrate the effect of the transition velocity behavior on traffic velocity and density. Simulation results are presented which show that this model provides a more accurate characterization of traffic flow behavior than the well known Payne-Whitham model. The proposed model can be used to reduce accidents and improve road safety during adverse weather conditions.

A new ellipse fitting method of the minimum differential-mode noise in the atom interference gravimeter

Aopeng Xu, Zhaoying Wang, Delong Kong, Zhijie Fu, Qiang Lin
Chin. Phys. B 2018, 27 (7): 070203;  doi: 10.1088/1674-1056/27/7/070203
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Ellipse fitting is a useful tool to obtain the differential signal of two atom interference gravimeters. The quality standard of ellipse fitting should be the deviation between the true phase and the fitting phase of the interference fringe. In this paper, we present a new algorithm to fit the ellipse. The algorithm is to minimize the differential noise of two interference gravimeters and obtain a more accurate value of the gravity gradient. We have theoretically derived the expression of the differential-mode noise and implemented the ellipse fitting in the program. This new algorithm is also compared with the classical methods.

Urban rail departure capacity analysis based on a cellular automaton model

Wen-Jun Li, Lei Nie
Chin. Phys. B 2018, 27 (7): 070204;  doi: 10.1088/1674-1056/27/7/070204
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As an important traffic mode, urban rail transit is constantly developing toward improvement in service capacity and quality. When an urban rail transit system is evaluated in terms of its service capacity, the train departure capacity is an important index that can objectively reflect the service level of an urban rail transit facility. In light of the existing cellular automaton models, this paper proposes a suitable cellular automaton model to analyze the train departure capacity of urban rail transit under different variable factors and conditions. The established model can demonstrate the train operating processes by implementing the proposed sound rules, including the rules of train departure at the origin and intermediate stations, and the velocity and position updating rules. The properties of train traffic are analyzed via numerical experiments. The numerical results show that the departure capacity is negatively affected by the train departure control manner. In addition, (i) the real-time signal control can offer a higher train service frequency; (ii) the departure capacity gradually rises with the decrease in the line design speed to a limited extent; (iii) the departure capacity decreases with extension in the train length; (iv) the number of departed trains decreases as the train stop time increases; (v) the departure capacity is not affected by the section length. However, the longer the length, the worse the service quality of the urban rail transit line. The experiments show that the proposed cellular automaton model can be used to analyze the train service capacity of an urban rail transit system by performing quantitative analysis under various considered factors, conditions, and management modes.

Uncertainty relations in the product form

Xiaofen Huang, Ting-Gui Zhang, Naihuan Jing
Chin. Phys. B 2018, 27 (7): 070302;  doi: 10.1088/1674-1056/27/7/070302
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We study the uncertainty relation in the product form of variances and obtain some new uncertainty relations with weight, which are shown to be tighter than those derived from the Cauchy-Schwarz inequality.

Phase precision of Mach-Zehnder interferometer in PM2.5 air pollution

Duan Xie, Haifeng Chen
Chin. Phys. B 2018, 27 (7): 070304;  doi: 10.1088/1674-1056/27/7/070304
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This paper theoretically explores the effect of PM2.5 air pollution on the phase precision of a Mach-Zehnder interferometer. With the increasing of PM2.5 concentration, phase precision for inputs of coherent state & vacuum state and inputs of coherent state & squeezed vacuum state will gradually decrease and be lower than the standard quantum limit. When the value of relative humidity is increasing, the precision of two input cases is decreasing much faster. We also find that the precision for inputs of coherent state & squeezed state is better than that of coherent state & vacuum state when PM2.5 concentration is lower. As PM2.5 concentration increases, the precision for inputs of coherent state & squeezed state decreases faster, and then the two precisions tend to be the same while the concentration is higher.

Continuous-variable quantum key distribution based on continuous random basis choice

Weiqi Liu, Jinye Peng, Peng Huang, Shiyu Wang, Tao Wang, Guihua Zeng
Chin. Phys. B 2018, 27 (7): 070305;  doi: 10.1088/1674-1056/27/7/070305
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Gaussian-modulated coherent state quantum key distribution is gradually moving towards practical application. Generally, the involved scheme is based on the binary random basis choice. To improve the performance and security, we present a scheme based on a continuous random basis choice. The results show that our scheme obviously improves the performance, such as the secure communication distance. Our scheme avoids comparing the measurement basis and discarding the key bits, and it can be easily implemented with current technology. Moreover, the imperfection of the basis choice can be well removed by the known phase compensation algorithm.

Generalized Lanczos method for systematic optimization of tensor network states

Rui-Zhen Huang, Hai-Jun Liao, Zhi-Yuan Liu, Hai-Dong Xie, Zhi-Yuan Xie, Hui-Hai Zhao, Jing Chen, Tao Xiang
Chin. Phys. B 2018, 27 (7): 070501;  doi: 10.1088/1674-1056/27/7/070501
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We propose a generalized Lanczos method to generate the many-body basis states of quantum lattice models using tensor-network states (TNS). The ground-state wave function is represented as a linear superposition composed from a set of TNS generated by Lanczos iteration. This method improves significantly the accuracy of the tensor-network algorithm and provides an effective way to enlarge the maximal bond dimension of TNS. The ground state such obtained contains significantly more entanglement than each individual TNS, reproducing correctly the logarithmic size dependence of the entanglement entropy in a critical system. The method can be generalized to non-Hamiltonian systems and to the calculation of low-lying excited states, dynamical correlation functions, and other physical properties of strongly correlated systems.

Multi-stability involved mixed bursting within the coupled pre-Bötzinger complex neurons

Zijian Wang, Lixia Duan, Qinyu Cao
Chin. Phys. B 2018, 27 (7): 070502;  doi: 10.1088/1674-1056/27/7/070502
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Neurons in the pre-Bötzinger complex within the mammalian brain stem play important roles in the generation of respiratory rhythms. Experimental observations show that some neurons can exhibit novel mixed bursting activities. In this paper, based on a mathematical model proposed by Butera, we show how the mixed bursting activities depend on the potassium current in the coupled pre-Botzinger complex. Using fast-slow decomposition and bifurcation analysis, we investigate the dynamics of mixed bursting, as well as the mechanisms of transition between different mixed bursting patterns. We find that mixed bursting involves different bistability, and it is the transition state of two types of regular burstings.

Fixed time integral sliding mode controller and its application to the suppression of chaotic oscillation in power system

Jiang-Bin Wang, Chong-Xin Liu, Yan Wang, Guang-Chao Zheng
Chin. Phys. B 2018, 27 (7): 070503;  doi: 10.1088/1674-1056/27/7/070503
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Chattering phenomenon and singularity are still the main problems that hinder the practical application of sliding mode control. In this paper, a fixed time integral sliding mode controller is designed based on fixed time stability theory, which ensures precise convergence of the state variables of controlled system, and overcomes the drawback of convergence time growing unboundedly as the initial value increases in finite time controller. It makes the controlled system converge to the control objective within a fixed time bounded by a constant as the initial value grows, and convergence time can be changed by adjusting parameters of controllers properly. Compared with other fixed time controllers, the fixed time integral sliding mode controller proposed in this paper achieves chattering-free control, and integral expression is used to avoid singularity generated by derivation. Finally, the controller is used to stabilize four-order chaotic power system. The results demonstrate that the controller realizes the non-singular chattering-free control of chaotic oscillation in the power system and guarantees the fixed time convergence of state variables, which shows its higher superiority than other finite time controllers.

Mean-square composite-rotating consensus of second-order systems with communication noises

Li-po Mo, Shao-yan Guo, Yong-guang Yu
Chin. Phys. B 2018, 27 (7): 070504;  doi: 10.1088/1674-1056/27/7/070504
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We study the mean-square composite-rotating consensus problem of second-order multi-agent systems with communication noises, where all agents rotate around a common center and the center of rotation spins around a fixed point simultaneously. Firstly, a time-varying consensus gain is introduced to attenuate to the effect of communication noises. Secondly, sufficient conditions are obtained for achieving the mean-square composite-rotating consensus. Finally, simulations are provided to demonstrate the effectiveness of the proposed algorithm.

A slope-based decoupling algorithm to simultaneously control dual deformable mirrors in a woofer-tweeter adaptive optics system

Tao Cheng, Wenjin Liu, Boqing Pang, Ping Yang, Bing Xu
Chin. Phys. B 2018, 27 (7): 070704;  doi: 10.1088/1674-1056/27/7/070704
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We propose a slope-based decoupling algorithm to simultaneously control the dual deformable mirrors (DMs) in a woofer-tweeter adaptive optics system. This algorithm can directly use the woofer's response matrix measured from a Shack-Hartmann wave-front sensor to construct a slope-based orthogonal basis, and then selectively distribute the large-amplitude low-order aberration to woofer DM and the remaining aberration to tweeter DM through the slope-based orthogonal basis. At the same moment, in order to avoid the two DMs generating opposite compensation, a constraint matrix used to reset tweeter control vector is convenient to be calculated with the slope-based orthogonal basis. Numeral simulation demonstrates that this algorithm has a good performance to control the adaptive optics system with dual DMs simultaneously. Compared with the typical decoupling algorithm, this algorithm can take full use of the compensation ability of woofer DM and release the stroke of tweeter DM to compensate high-order aberration. More importantly, it does not need to measure the accurate shape of tweeter's influence function and keeps better performance of restraining the coupling error with the continuous-dynamic aberration.
SPECIAL TOPIC—Recent advances in thermoelectric materials and devices

Relativistic calculations of fine-structure energy levels of He-like Ar in dense plasmas

Xiang-Fu Li, Gang Jiang
Chin. Phys. B 2018, 27 (7): 073101;  doi: 10.1088/1674-1056/27/7/073101
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The fine-structure energy levels of 1s2s and 1s2p atomic states for the He-like Ar ion immersed in dense plasmas are calculated. The ion sphere model is used to describe the plasma screening effect on the tested ion. The influences of the hard sphere confinement and plasma screening on the fine-structure energy levels are investigated respectively. The calculated results show that the confined effect of the hard sphere on the fine-structure energy levels increases with decreasing hard sphere radius, and the plasma screening effect on the fine-structure energy levels increases with the increase of free electron density. In dense plasmas, the confined effect of the hard sphere on the fine-structure energy levels can be neglected generally, compared with the contribution from free electron screening. An interesting phenomenon about the energy level crossing is found among 1s2s (1S0) and 1s2p (3P0,1) atomic states. The results reported at the present work are useful for plasma diagnostics.

Slater determinant and exact eigenstates of the two-dimensional Fermi-Hubbard model

Jun-Hang Ren, Ming-Yong Ye, Xiu-Min Lin
Chin. Phys. B 2018, 27 (7): 073102;  doi: 10.1088/1674-1056/27/7/073102
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We consider the construction of exact eigenstates of the two-dimensional Fermi-Hubbard model defined on an L×L lattice with a periodic condition. Based on the characteristics of Slater determinants, several methods are introduced to construct exact eigenstates of the model. The eigenstates constructed are independent of the on-site electron interaction and some of them can also represent exact eigenstates of the two-dimensional Bose-Hubbard model.

Diffusion behavior of hydrogen isotopes in tungsten revisited by molecular dynamics simulations

Mingjie Qiu, Lei Zhai, Jiechao Cui, Baoqin Fu, Min Li, Qing Hou
Chin. Phys. B 2018, 27 (7): 073103;  doi: 10.1088/1674-1056/27/7/073103
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Molecular dynamics simulations were performed to study the diffusion behavior of hydrogen isotopes in single-crystal tungsten in the temperature range of 300-2000 K. The simulations show that the diffusion coefficient of H isotopes exhibits non-Arrhenius behavior, though this deviation from Arrhenius behavior is slight. Many-body and anharmonic effects of the potential surface may induce slight isotope-dependence by the activation energy; however, the dependence of the pre-factor of the diffusion coefficient on the isotope mass is diminished. The simulation results for H-atom migration near W surfaces suggest that no trap mutations occur for H atoms diffusing near either W{100} or W{111} surfaces, in contrast to the findings for He diffusion near W surfaces. Based on the H behavior obtained by our MD simulations, the time evolution of the concentration distribution of interstitial H atoms in a semi-infinite W single crystal irradiated by energetic H projectiles was calculated. The effect of H concentration on H diffusion is discussed, and the applicability of the diffusion coefficients obtained for dilute H in W is assessed.

Transverse relaxation determination based on light polarization modulation for spin-exchange relaxation free atomic magnetometer

Xue-Jing Liu, Ming Ding, Yang Li, Yan-Hui Hu, Wei Jin, Jian-Cheng Fang
Chin. Phys. B 2018, 27 (7): 073201;  doi: 10.1088/1674-1056/27/7/073201
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A transverse relaxation determination of spin-exchange relaxation free (SERF) magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency (RF) excitation and light intensity excitation methods used in SERF magnetometer, the light polarization modulation method has a high stability in low-frequency range, which indicates a more accurate transverse relaxation measurement.

Effect of electron excitation in nonsequential double ionization by intense laser fields

Xiang Chen, Qiujing Han, Jingtao Zhang
Chin. Phys. B 2018, 27 (7): 073202;  doi: 10.1088/1674-1056/27/7/073202
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We study the double ionization process of atoms in intense laser fields. The momentum distributions of the correlated electrons are calculated. Contrary to the general expectation, we show an increasing proportion of the electrons ionized via excitation with the increasing laser intensity. These electrons generally have small energy thus they concentratedly distribute on the central region of the momentum diagram. Consequently, the central part of the momentum diagram becomes more notable in higher intensity laser fields. Further study suggests that this phenomenon is general in double ionization.

Above-threshold ionization of hydrogen atom in chirped laser fields

Yuan-Yuan Ni, Song-Feng Zhao, Xiao-Yong Li, Guo-Li Wang, Xiao-Xin Zhou
Chin. Phys. B 2018, 27 (7): 073203;  doi: 10.1088/1674-1056/27/7/073203
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Above-threshold ionization (ATI) of a hydrogen atom exposed to chirped laser fields is investigated theoretically by solving the time-dependent Schrödinger equation. By comparing the energy spectra, the two-dimensional momentum spectra, and the angular distributions of photoelectron for the laser pulses with different chirp rates, we show a very clear chirp dependence both in the multiphoton and tunneling ionization processes but no chirp dependence in the single-photon ionization. We find that the chirp dependence in the multiphoton ionization based ATI can be attributed to the excited bound states. In the single-photon and tunneling ionization regimes, the electron can be removed directly from the ground state and thus the excited states may not be very important. It indicates that the chirp dependence in the tunneling ionization based ATI processes is mainly due to the laser pulses with different chirp rates.

High-order harmonic generation in a two-color strong laser field with Bohmian trajectory theory

Yi-Yi Huang, Xuan-Yang Lai, Xiao-Jun Liu
Chin. Phys. B 2018, 27 (7): 073204;  doi: 10.1088/1674-1056/27/7/073204
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We theoretically study the high-order harmonic generation (HHG) in a two-color laser field using the Bohmian mechanics. Our results show that, for the case of a weak second-color laser field, the simulation of the HHG with only one central Bohmian trajectory is in a good agreement with the ab initio time-dependent Schrödinger equation (TDSE) results. In contrast, with the increase of the amplitude of the second-color laser field, the HHG spectra from the single central Bohmian trajectory deviate from the TDSE results more and more significantly. By analyzing the Bohmian trajectories, we find that the significant deviation is due to the fact that the central Bohmian trajectory leaves the core quickly in the two-color laser field with the breaking of inversion symmetry. Interestingly, we find that another Bohmian trajectory with different initial position, which keeps oscillating around the core, could qualitatively well reproduce the TDSE results. Furthermore, we study the HHG spectrum in a two-color laser field with inversion symmetry and find that the HHG spectrum in TDSE can be still well simulated with the central Bohmian trajectory. These results indicate that, similar to the case of one color laser field, the HHG spectra in a two-color laser field can be also reproduced with a single Bohmian trajectory, although the initial position of the trajectory is dependent on the symmetry of the laser field. Our work thus demonstrates that Bohmian trajectory theory can be used as a promising tool in investigating the HHG process in a two-color laser field.

High-order harmonic generation of Li+ with combined infrared and extreme ultraviolet fields

Li Wang, Guo-Li Wang, Zhi-Hong Jiao, Song-Feng Zhao, Xiao-Xin Zhou
Chin. Phys. B 2018, 27 (7): 073205;  doi: 10.1088/1674-1056/27/7/073205
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We investigate high-order harmonic generation (HHG) of Li+ ion driven by an intense infrared (IR) laser field in combination with a weak XUV pulse. To achieve this, we first construct an accurate single-active electron angular-momentum-dependent model potential of Li+ ion, by which the accurate singlet energy levels of Li+ for the ground state and excited states with higher quantum numbers can be obtained. Then, we solve numerically the three dimensional time-dependent Schrödinger equation of Li+ ion by means of the generalized pseudospectral method to obtain HHG. Our results show that the strength of assisted XUV is not amplified during the harmonic generation process, but the yield of HHG power spectrum in the whole plateau has a significant enhancement. Furthermore, the optimal phase delay between the IR and XUV pulses allows the production of ultrabroadband supercontinuum spectra. By superposing some harmonics, a strong new single 27-attosecond ultrashort pulse can be obtained.

Loss of cold atoms due to collisions with residual gases in free flight and in a magneto-optical trap

Jing-feng Xiang, He-nan Cheng, Xiang-kai Peng, Xin-wen Wang, Wei Ren, Jing-wei Ji, Kang-kang Liu, Jian-bo Zhao, Lin Li, Qiu-zhi Qu, Tang Li, Bin Wang, Mei-feng Ye, Xin Zhao, Yuan-yuan Yao, De-Sheng Lü, Liang Liu
Chin. Phys. B 2018, 27 (7): 073701;  doi: 10.1088/1674-1056/27/7/073701
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The loss rate of cold atoms in a trap due to residual gas collisions differs from that in a free state after the cold atoms are released from the trap. In this paper, the loss rate in a cold rubidium-87 atom cloud was measured in a magneto-optical trap (MOT) and during its free flight. The residual gas pressure was analyzed by a residual gas analyzer, and the pressure distribution in a vacuum chamber was numerically calculated by the angular coefficient method. The decay factor, which describes the decay behavior of cold atoms due to residual gas collisions during a free flight, was calculated. It was found that the decay factor agrees well with theoretical predictions under various vacuum conditions.


Reliable approach for bistatic scattering of three-dimensional targets from underlying rough surface based on parabolic equation

Dong-Min Zhang, Cheng Liao, Liang Zhou, Xiao-Chuan Deng, Ju Feng
Chin. Phys. B 2018, 27 (7): 074102;  doi: 10.1088/1674-1056/27/7/074102
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A parabolic equation (PE) based method for analyzing composite scattering under an electromagnetic wave incidence at low grazing angle, which composes of three-dimensional (3-D) electrically large targets and rough surface, is presented and discussed. A superior high-order PE version is used to improve the accuracy at wider paraxial angles, and along with the alternating direction implicit (ADI) differential technique, the computational efficiency is further improved. The formula of bistatic normalized radar cross section is derived by definition and near-far field transformation. Numerical examples are given to show the validity and accuracy of the proposed approach, in which the results are compared with those of Kirchhoff approximation (KA) and moment of method (MoM). Furthermore, the bistatic scattering properties of composite model in which the 3-D PEC targets on or above the two-dimensional Gaussian rough surfaces under the tapered wave incidence are analyzed.

Flexible control of semiconductor laser with frequency tunable modulation transfer spectroscopy

Ning Ru, Yu Wang, Hui-Juan Ma, Dong Hu, Li Zhang, Shang-Chun Fan
Chin. Phys. B 2018, 27 (7): 074201;  doi: 10.1088/1674-1056/27/7/074201
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We introduce a new method of simultaneously implementing frequency stabilization and frequency shift for semiconductor lasers. We name this method the frequency tunable modulation transfer spectroscopy (FTMTS). To realize a stable output of 780 nm semiconductor laser, an FTMTS optical heterodyne frequency stabilization system is constructed. Before entering into the frequency stabilization system, the probe laser passes through an acousto-optical modulator (AOM) twice in advance to achieve tunable frequency while keeping the light path stable. According to the experimental results, the frequency changes from 120 MHz to 190 MHz after the double-pass AOM, and the intensity of laser entering into the system is greatly changed, but there is almost no change in the error signal of the FTMTS spectrum. Using this signal to lock the laser frequency, we can ensure that the frequency of the laser changes with the amount of AOM shift. Therefore, the magneto-optical trap (MOT)-molasses process can be implemented smoothly.

Super-resolution imaging via sparsity constraint and sparse speckle illumination

Pengwei Wang, Wei Li, Chenglong Wang, Zunwang Bo, Wenlin Gong
Chin. Phys. B 2018, 27 (7): 074202;  doi: 10.1088/1674-1056/27/7/074202
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We present an imaging approach via sparsity constraint and sparse speckle illumination which can dramatically enhance the optical system's imaging resolution. When the object is illuminated by some sparse speckles and the sparse reconstruction algorithm is utilized to restore the blur image, numerical simulated results demonstrate that the image, whose resolution exceeds the Rayleigh limit, can be stably reconstructed even if the detection signal-to-noise ratio (SNR) is less than 10 dB. Factors affecting the quality of the reconstructed image, such as the coded pattern's sparsity and the detection SNR, are also studied.

Multiple-image encryption by two-step phase-shifting interferometry and spatial multiplexing of smooth compressed signal

Xue Zhang, Xiangfeng Meng, Yurong Wang, Xiulun Yang, Yongkai Yin
Chin. Phys. B 2018, 27 (7): 074205;  doi: 10.1088/1674-1056/27/7/074205
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A multiple-image encryption method based on two-step phase-shifting interferometry (PSI) and spatial multiplexing of a smooth compressed signal is proposed. In the encoding and encryption process, with the help of four index matrices to store original pixel positions, all the pixels of four secret images are firstly reordered in an ascending order; then, the four reordered images are transformed by five-order Haar wavelet transform and performed sparseness operation. After Arnold transform and pixels sampling operation, one combined image can be grouped with the aid of compressive sensing (CS) and spatial multiplexing techniques. Finally, putting the combined image at the input plane of the PSI encryption scheme, only two interferograms ciphertexts can be obtained. During the decoding and decryption, utilizing all the secret key groups and index matrices keys, all the original secret images can be successfully decrypted by a wave-front retrieval algorithm of two-step PSI, spatial de-multiplexing, inverse Arnold transform, inverse discrete wavelet transform, and pixels reordering operation.

Modulation of energy spectrum and control of coherent microwave transmission at single-photon level by longitudinal field in a superconducting quantum circuit

Xueyi Guo, Hui Deng, Hekang Li, Pengtao Song, Zhan Wang, Luhong Su, Jie Li, Yirong Jin, Dongning Zheng
Chin. Phys. B 2018, 27 (7): 074206;  doi: 10.1088/1674-1056/27/7/074206
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We study the effect of longitudinally applied field modulation on a two-level system using superconducting quantum circuits. The presence of the modulation results in additional transitions and changes the magnitude of the resonance peak in the energy spectrum of the qubit. In particular, when the amplitude λz and the frequency ωl of the modulation field meet certain conditions, the resonance peak of the qubit disappears. Using this effect, we further demonstrate that the longitudinal field modulation of the Xmon qubit coupled to a one-dimensional transmission line could be used to dynamically control the transmission of single-photon level coherent resonance microwave.

A sensitive detection of high Rydberg atom with large dipole moment

Shan-Shan Zhang, Hong Cheng, Pei-Pei Xin, Han-Mu Wang, Zi-Shan Xu, Hong-Ping Liu
Chin. Phys. B 2018, 27 (7): 074207;  doi: 10.1088/1674-1056/27/7/074207
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We report a sensitive detection of high Rydberg atom with large dipole moment utilizing its deflection near a pair of parallel cylindrical copper rods which are oppositely charged. When the low-field seeking state Rydberg atoms fly across the gradient electric field formed by the pair of rods, they will be pushed away from the rods while the high-field seeking state ones will be attracted towards the rods. These atoms will form different patterns on an ion imaging system placed downwards at the end of the rods. The spatial distribution of the deflected atoms on the imaging system is also simulated, in good agreement with the experimental results, from which we can deduce the quantum state information of the excited atoms. This state resolvable Rydberg atom detection can be used for the dynamics research of the dipole-dipole interaction between atoms with large dipole moments.

Estimation of photon counting statistics with imperfect detectors

Xiao-Chuan Han, Dong-Wei Zhuang, Yu-Xuan Li, Jun-Feng Song, Yong-Sheng Zhang
Chin. Phys. B 2018, 27 (7): 074208;  doi: 10.1088/1674-1056/27/7/074208
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The study on photon counting statistics is of fundamental importance in quantum optics. We theoretically analyzed the imperfect detection of an arbitrary quantum state. We derived photon counting formulae for six typical quantum states (i.e., Fock, coherent, squeeze-vacuum, thermal, odd and even coherent states) with finite quantum efficiencies and dark counts based on multiple on/off detector arrays. We applied the formulae to the simulation of multiphoton number detections and obtained both the simulated and ideal photon number distributions of each state. A comparison between the results by using the fidelity and relative entropy was carried out to evaluate the detection scheme and help select detectors for different quantum states.

Entangling two oscillating mirrors in an optomechanical system via a flying atom

Yu-Bao Zhang, Jun-Hao Liu, Ya-Fei Yu, Zhi-Ming Zhang
Chin. Phys. B 2018, 27 (7): 074209;  doi: 10.1088/1674-1056/27/7/074209
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We propose a novel scheme for generating the entanglement of two oscillating mirrors in an optomechanical system via a flying atom. In this scheme, a two-level atom, in an arbitrary superposition state, passes through an optomechanical system with two oscillating cavity-mirrors, and then its states are detected. In this way, we can generate the entangled states of the two oscillating mirrors. We derive the analytical expressions of the entangled states and make numerical calculations. We find that the entanglement of the two oscillating mirrors can be controlled by the initial state of the atom, the optomechanical coupling strength, and the coupling strength between the atom and the cavity field. We investigate the dynamics of the system with dissipations and discuss the experimental feasibility.

Novel single-transverse-mode control of VCSELs with dielectric mode filter

Lei Xiang, Xing Zhang, Jian-Wei Zhang, You-Wen Huang, Yong-Qiang Ning, Li-Jun Wang
Chin. Phys. B 2018, 27 (7): 074210;  doi: 10.1088/1674-1056/27/7/074210
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We establish a novel method of controlling the transverse modes of vertical cavity surface emitting lasers (VCSELs) to achieve 1 mW single-fundamental-mode lasing. A dielectric mode filter is installed on top of the VCSEL. The dielectric layer (SiO2) is deposited and patterned to modify the mirror reflectivity across the oxide aperture via antiphase reflections. This mode selection is nondestructive and universally applicable for other structures under single transverse mode. Destructive etching techniques (dry/wet) or epitaxial regrowth are also not required. This method simplifies the preparation process and improves the repeatability of the device. Measurements show that under continuous-wave current injection, the side-mode suppression ratio exceeds 30 dB.

Linear polarization output performance of Nd: YAG laser at 946 nm considering the energy-transfer upconversion

Jin-Xia Feng, Yuan-Ji Li, Kuan-Shou Zhang
Chin. Phys. B 2018, 27 (7): 074211;  doi: 10.1088/1674-1056/27/7/074211
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A theoretical model of quasi-three-level laser system is developed, in which both the thermally induced depolarization loss and the effect of energy-transfer upconversion are taken into account. Based on the theoretical investigation of the influences of output transmission and incident pump power on thermally induced depolarization loss, the output performance of 946 nm linearly polarized Nd:YAG laser is experimentally studied. By optimizing the transmission of output coupler, a 946 nm linearly polarized continuous-wave single-transverse-mode laser with an output power of 4.2 W and an optical-optical conversion efficiency of 16.8% is obtained, and the measured beam quality factors are Mx2=1.13 and My2=1.21. The theoretical prediction is in good agreement with the experimental result.

Coupled resonator-induced transparency on a three-ring resonator

Xinquan Jiao, Haobo Yu, Miao Yu, Chenyang Xue, Yongfeng Ren
Chin. Phys. B 2018, 27 (7): 074212;  doi: 10.1088/1674-1056/27/7/074212
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The coupled resonator-induced transparency (CRIT) phenomenon, which is analogous to electromagnetically induced transparency in atomic systems, can occur in an original integrated optical resonator system due to the coherent interference of the coupled optical resonators. The system was composed of three ring resonators on silicon, each with the same cavity size, and the optical coupling to the input and output ports was achieved using grating with a power coupling efficiency of 36%. A CRIT resonance whose spectrum shows a narrow transparency peak with a low group velocity was demonstrated. The quality factor of the ring resonator can attain a value up to 6×104, and the harmonic wavelength can be controlled by adjusting the temperature. The through and drop transmission spectra of the resonator are reconciled well with each other and also consistent well with the theoretical analysis.

Laser absorption spectroscopy for high temperature H2O time-history measurement at 2.55 μm during oxidation of hydrogen

Yu-Dan Gou, De-Xiang Zhang, Yi-Jun Wang, Chang-Hua Zhang, Ping Li, Xiang-Yuan Li
Chin. Phys. B 2018, 27 (7): 074213;  doi: 10.1088/1674-1056/27/7/074213
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Concentration time-histories of H2O were measured behind reflected shock waves during hydrogen combustion. Experiments were conducted at temperatures of 1117-1282 K, the equivalence ratios of 0.5 and 0.25, and a pressure at 2 atm using a mixture of H2/O2 highly diluted with argon. H2O was monitored using tunable mid-infrared diode laser absorption at 2.55 μm (3920.09 cm-1). These time-histories provide kinetic targets to test and refine reaction mechanisms for hydrogen. Comparisons were made with the predictions of four detailed kinetic mechanisms published in the last four years. Such comparisons of H2O concentration profiles indicate that the AramcoMech 2.0 mechanism yields the best agreement with the experimental data, while CRECK, San Diego, and HP-Mech mechanisms show significantly poor predictions. Reaction pathway analysis for hydrogen oxidation indicates that the reaction H+OH+M=H2O+M is the key reaction for controlling the H2O formation by hydrogen oxidation. It is inferred that the discrepancy of the conversion percentage from H to H2O among these four mechanisms induces the difference of performance on H2O time-history predictions. This work demonstrates the potential of time-history measurement for validation of large reaction mechanisms.

Controllable optical bistability in a three-mode optomechanical system with a membrane resonator

Jiakai Yan, Xiaofei Zhu, Bin Chen
Chin. Phys. B 2018, 27 (7): 074214;  doi: 10.1088/1674-1056/27/7/074214
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We study the optical bistability (OB) in a three-mode cavity optomechanical system, where an oscillating membrane of perfect reflection is inserted between two fixed mirrors of partial transmission. By investigating the behavior of steady state solutions, we find that the left and right cavities will exhibit the bistable behavior simultaneously in this optomechanical system by adjusting the left and right coupling fields. In addition, one can control the OB threshold and the width of the OB curve via adjusting the coupling strength, the detuning, and the decay rate. Moreover, we further illustrate the OB appearing in the cavity by the effective potential as a function of the position.

Decaying solitary waves propagating in one-dimensional damped granular chain

Zongbin Song, Xueying Yang, Wenxing Feng, Zhonghong Xi, Liejuan Li, Yuren Shi
Chin. Phys. B 2018, 27 (7): 074501;  doi: 10.1088/1674-1056/27/7/074501
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We numerically investigate the nonlinear waves propagating in a one-dimensional particle chain when the damping effect is taken into account. It is found that decaying solitary waves exist, in which the amplitude of the wave decreases exponentially as time increases. Meanwhile, the velocity of the solitary wave also slows down as time goes. This result implies that the damping coefficient is an important parameter in such a nonlinear system. Theoretical analysis has also been done by the reductive perturbation method. The result indicates that the nonlinear waves propagating in such a system can be described by the damped KdV equation.

Interaction between many parallel screw dislocations and a semi-infinite crack in a magnetoelectroelastic solid

Xin Lv, Guan-Ting Liu
Chin. Phys. B 2018, 27 (7): 074601;  doi: 10.1088/1674-1056/27/7/074601
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Based on the fundamental equations of magnetoelectroelastic material and the analytic theory, and using the Muskhelishvili-introduced well-known elastic techniques combined with the superposition principle, the closed form solution of the generalized stress field of the interaction between many parallel screw dislocations and a semi-infinite crack in an infinite magnetoelectroelastic solid is obtained, on the assumption that the surface of the crack is impermeable electrically and magnetically. Besides, the Peach-Koehler formula of n parallel screw dislocations is given. Numerical examples show that the generalized stress varies with the position of point z and is related to the material constants. The results indicate that the stress concentration occurs at the dislocation core and the tip of the crack. The result of interaction makes the system stay in a lower energy state.

Active control of wall-bounded turbulence for drag reduction with piezoelectric oscillators

Jian-Xia Bai, Nan Jiang, Xiao-Bo Zheng, Zhan-Qi Tang, Kang-Jun Wang, Xiao-Tong Cui
Chin. Phys. B 2018, 27 (7): 074701;  doi: 10.1088/1674-1056/27/7/074701
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An experimental investigation was performed for active control of coherent structure bursting in the near-wall region of the turbulent boundary layer. By means of synchronous and asynchronous vibrations with double piezoelectric vibrators, the influence of periodic vibration of the double piezoelectric vibrators on the mean velocity profile, drag reduction rate, and coherent structure bursting is analyzed at Reθ=2766. The case with 100 V/160 Hz-ASYN is superior to other conditions in the experiment and a relative drag reduction rate of 18.54% is exciting. Asynchronous vibration is more effective than synchronous vibration in drag reduction at the same voltage and frequency. In all controlled cases, coherent structures at large scales are regulated while the small-scale structures are stimulated. The fluctuating velocity increases significantly. A periodic regulating effect on the coherent structure can be seen in the ASYN control conditions at the frequency of 160 Hz.

Investigation of flux dependent sensitivity on single event effect in memory devices

Jie Luo, Tie-shan Wang, Dong-qing Li, Tian-qi Liu, Ming-dong Hou, You-mei Sun, Jing-lai Duan, Hui-jun Yao, Kai Xi, Bing Ye, Jie Liu
Chin. Phys. B 2018, 27 (7): 076101;  doi: 10.1088/1674-1056/27/7/076101
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Heavy-ion flux is an important experimental parameter in the ground based single event tests. The flux impact on a single event effect in different memory devices is analyzed by using GEANT4 and TCAD simulation methods. The transient radial track profile depends not only on the linear energy transfer (LET) of the incident ion, but also on the mass and energy of the ion. For the ions with the energies at the Bragg peaks, the radial charge distribution is wider when the ion LET is larger. The results extracted from the GEANT4 and TCAD simulations, together with detailed analysis of the device structure, are presented to demonstrate phenomena observed in the flux related experiment. The analysis shows that the flux effect conclusions drawn from the experiment are intrinsically connected and all indicate the mechanism that the flux effect stems from multiple ion-induced pulses functioning together and relies exquisitely on the specific response of the device.

Band engineering of double-wall Mo-based hybrid nanotubes

Lei Tao, Yu-Yang Zhang, Jiatao Sun, Shixuan Du, Hong-Jun Gao
Chin. Phys. B 2018, 27 (7): 076104;  doi: 10.1088/1674-1056/27/7/076104
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Hybrid transition-metal dichalcogenides (TMDs) with different chalcogens on each side (X-TM-Y) have attracted attention because of their unique properties. Nanotubes based on hybrid TMD materials have advantages in flexibility over conventional TMD nanotubes. Here we predict the wide band gap tunability of hybrid TMD double-wall nanotubes (DWNTs) from metal to semiconductor. Using density-function theory (DFT) with HSE06 hybrid functional, we find that the electronic property of X-Mo-Y DWNTs (X=O and S, inside a tube; Y=S and Se, outside a tube) depends both on electronegativity difference and diameter difference. If there is no difference in electron negativity between inner atoms (X) of outer tube and outer atoms (Y) of inner tube, the band gap of DWNTs is the same as that of the inner one. If there is a significant electronegativity difference, the electronic property of the DWNTs ranges from metallic to semiconducting, depending on the diameter differences. Our results provide alternative ways for the band gap engineering of TMD nanotubes.

Co-adsorption of O2 and H2O on α-uranium (110) surface: A density functional theory study

Xin Qu, Ru-Song Li, Bin He, Fei Wang, Kai-Long Yuan
Chin. Phys. B 2018, 27 (7): 076501;  doi: 10.1088/1674-1056/27/7/076501
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First-principles calculations based on density functional theory corrected by Hubbard parameter U (DFT+U) are applied to the study on the co-adsorption of O2 and H2O molecules to α-U(110) surface. The calculation results show that DFT+U method with Ueff=1.5 eV can yield the experimental results of lattice constant and elastic modulus of α-uranium bulk well. Of all 7 low index surfaces of α-uranium, the (001) surface is the most stable with lowest surface energy while the (110) surface possesses the strongest activity with the highest surface energy. The adsorptions of O2 and H2O molecules are investigated separated. The O2 dissociates spontaneously in all initial configurations. For the adsorption of H2O molecule, both molecular and dissociative adsorptionsoccur. Through calculations of co-adsorption, it can be confirmed that the inhibition effect of O2 on the corrosion of uranium by water vapor originates from the preferential adsorption mechanism, while the consumption of H atoms by O atoms exerted little influence on the corrosion of uranium.

Thermal conductivity of systems with a gap in the phonon spectrum

E Salamatov
Chin. Phys. B 2018, 27 (7): 076502;  doi: 10.1088/1674-1056/27/7/076502
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An original theoretical model for describing the low-temperature thermal conductivity in systems with a region of forbidden values (a gap) in the phonon spectrum is proposed. The model is based on new experimental results on the temperature dependence of the phonon diffusion coefficient in nanoceramics and dielectric glasses which showed a similar anomalous behavior of the diffusion coefficient in these systems that may be described under the assumption of a gap in the phonon spectrum. In this paper, the role of the gap in low-temperature behavior of the thermal conductivity, κ (T), is analyzed. The plateau in the temperature dependence of the thermal conductivity is shown to correlate with the position and the width of the gap. The temperature dependence of thermal conductivity of such systems when changing the scattering parameters related to various mechanisms is studied. It is found that the umklapp process (U-processes) involving low-frequency short-wavelength phonons below the gap forms the behavior of the temperature dependence of thermal conductivity in the plateau region. A comparison of the calculated and experimental results shows considerable possibilities of the model in describing the low-temperature thermal conductivity in glass-like systems.

Growth and transport properties of topological insulator Bi2Se3 thin film on a ferromagnetic insulating substrate

Shanna Zhu, Gang Shi, Peng Zhao, Dechao Meng, Genhao Liang, Xiaofang Zhai, Yalin Lu, Yongqing Li, Lan Chen, Kehui Wu
Chin. Phys. B 2018, 27 (7): 076801;  doi: 10.1088/1674-1056/27/7/076801
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Exchange coupling between topological insulator and ferromagnetic insulator through proximity effect is strongly attractive for both fundamental physics and technological applications. Here we report a comprehensive investigation on the growth behaviors of prototype topological insulator Bi2Se3 thin film on a single-crystalline LaCoO3 thin film on SrTiO3 substrate, which is a strain-induced ferromagnetic insulator. Different from the growth on other substrates, the Bi2Se3 films with highest quality on LaCoO3 favor a relatively low substrate temperature during growth. As a result, an inverse dependence of carrier mobility with the substrate temperature is found. Moreover, the magnetoresistance and coherence length of weak antilocalization also have a similar inverse dependence with the substrate temperature, as revealed by the magnetotransport measurements. Our experiments elucidate the special behaviors in Bi2Se3/LaCoO3 heterostructures, which provide a good platform for exploring related novel quantum phenomena, and are inspiring for device applications.


Observation of geometric phase in a dispersively coupled resonator-qutrit system Hot!

Libo Zhang, Chao Song, H Wang, Shi-Biao Zheng
Chin. Phys. B 2018, 27 (7): 070303;  doi: 10.1088/1674-1056/27/7/070303
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We present an experiment of observing the geometric phase in a superconducting circuit where the resonator and the qutrit energy levels are dispersively coupled. The drive applied to the resonator displaces its state components associated with the qutrit's ground state and first-excited state along different circular trajectories in phase space. We identify the resonator's phase-space trajectories by Wigner tomography using an ancilla qubit, following which we observe the difference between the geometric phases associated with these trajectories using Ramsey interferometry. This geometric phase is further used to construct the single-qubit π-phase gate with a process fidelity of 0.851±0.001.

Momentum distribution and non-local high order correlation functions of 1D strongly interacting Bose gas Hot!

EJKP Nandani, Xi-Wen Guan
Chin. Phys. B 2018, 27 (7): 070306;  doi: 10.1088/1674-1056/27/7/070306
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The Lieb-Liniger model is a prototypical integrable model and has been turned into the benchmark physics in theoretical and numerical investigations of low-dimensional quantum systems. In this note, we present various methods for calculating local and nonlocal M-particle correlation functions, momentum distribution, and static structure factor. In particular, using the Bethe ansatz wave function of the strong coupling Lieb-Liniger model, we analytically calculate the two-point correlation function, the large moment tail of the momentum distribution, and the static structure factor of the model in terms of the fractional statistical parameter α=1-2/γ, where γ is the dimensionless interaction strength. We also discuss the Tan's adiabatic relation and other universal relations for the strongly repulsive Lieb-Liniger model in terms of the fractional statistical parameter.

Charge noise acting on graphene double quantum dots in circuit quantum electrodynamics architecture

Yan Li, Shu-Xiao Li, Hai-Ou Lidag, Guang-Wei Deng, Gang Cao, Ming Xiao, Guo-Ping Guo
Chin. Phys. B 2018, 27 (7): 076105;  doi: 10.1088/1674-1056/27/7/076105
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We investigate the dephasing mechanisms induced by the charge noise and microwave heating effect acting on a graphene double quantum dot (DQD) capacitively coupled to a microwave resonator. The charge noise is obtained from DC transport current, and its contribution to dephasing is simultaneously determined by the amplitude response of the microwave resonator. A lowfrequency 1/f-type noise is demonstrated to be the dominant factor of the dephasing of graphene DQD. Furthermore, when the applied microwave power is larger than-90 dBm, the dephasing rate of graphene DQD increases rapidly with the increase of microwave power, and fluctuates slightly with the applied microwave power smaller than-90 dBm. Our results can be applied to suppress the impeditive influence on the dephasing of graphene-based devices associated with microwave input in the perspective investigations.

Image charge effect on the light emission of rutile TiO2(110) induced by a scanning tunneling microscope Hot!

Chaoyu Guo, Xiangzhi Meng, Qin Wang, Ying Jiang
Chin. Phys. B 2018, 27 (7): 077301;  doi: 10.1088/1674-1056/27/7/077301
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The plasmon-enhanced light emission of rutile TiO2(110) surface has been investigated by a low-temperature scanning tunneling microscope (STM). We found that the photon emission arises from the inelastic electron tunneling between the STM tip and the conduction band or defect states of TiO2(110). In contrast to the Au(111) surface, the maximum photon energy as a function of the bias voltage clearly deviates from the linear scaling behavior, suggesting the non-negligible effect of the STM tip on the band structure of TiO2. By performing differential conductance (dI/dV) measurements, it was revealed that such a deviation is not related to the tip-induced band bending, but is attributed to the image charge effect of the metal tip, which significantly shifts the band edges of the TiO2(110) towards the Femi level (EF) during the tunneling process. This work not only sheds new lights onto the understanding of plasmon-enhanced light emission of semiconductor surfaces, but also opens up a new avenue for engineering the plasmon-mediated interfacial charge transfer in molecular and semiconducting materials.

Structural phase transition, precursory electronic anomaly, and strong-coupling superconductivity in quasi-skutterudite (Sr1-xCax)3Ir4Sn13 and Ca3Rh4Sn13 Hot!

Jun Luo, Jie Yang, S Maeda, Zheng Li, Guo-Qing Zheng
Chin. Phys. B 2018, 27 (7): 077401;  doi: 10.1088/1674-1056/27/7/077401
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The interplay between superconductivity and structural phase transition has attracted enormous interest in recent years. For example, in Fe-pnictide high temperature superconductors, quantum fluctuations in association with structural phase transition have been proposed to lead to many novel physical properties and even the superconductivity itself. Here we report a finding that the quasi-skutterudite superconductors (Sr1-xCax)3Ir4Sn13 (x=0, 0.5, 1) and Ca3Rh4Sn13 show some unusual properties similar to the Fe-pnictides, through 119Sn nuclear magnetic resonance (NMR) measurements. In (Sr1-xCax)3Ir4Sn13, the NMR linewidth increases below a temperature T* that is higher than the structural phase transition temperature Ts. The spin-lattice relaxation rate (1/T1) divided by temperature (T), 1/T1T and the Knight shift K increase with decreasing T down to T*, but start to decrease below T*, and followed by more distinct changes at Ts. In contrast, none of the anomalies is observed in Ca3Rh4Sn13 that does not undergo a structural phase transition. The precursory phenomenon above the structural phase transition resembles that occurring in Fe-pnictides. In the superconducting state of Ca3Ir4Sn13, 1/T1 decays as exp(-/kBT) with a large gap =2.21 kBTc, yet without a Hebel-Slichter coherence peak, which indicates strong-coupling superconductivity. Our results provide new insight into the relationship between superconductivity and the electronic-structure change associated with structural phase transition.


Robustness of coherence between two quantum dots mediated by Majorana fermions

Liang Chen, Ye-Qi Zhang, Rong-Sheng Han
Chin. Phys. B 2018, 27 (7): 077102;  doi: 10.1088/1674-1056/27/7/077102
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We study three important measurements used to identify the quantum correlations between two quantum dots (QDs) mediated by a pair of Majorana fermions (MFs) in a superconducting quantum wire. We find that, in addition to the quantum discord, the robustness of coherence (ROC) can also be considered as a quantity to measure the quantum correlation for the special case where the quantum entanglement is vanishing. For comparison, we study the quantum correlation between two QDs mediated by other fermions, i.e., regular fermions and superconducting fermions. We find that, when the quantum entanglement is not vanishing, i.e., the concurrence is finite, the detailed difference between the concurrence and ROC can be considered as an important implication for the existence of MFs.

Anisotropic elastic properties and ideal uniaxial compressive strength of TiB2 from first principles calculations

Min Sun, Chong-Yu Wang, Ji-Ping Liu
Chin. Phys. B 2018, 27 (7): 077103;  doi: 10.1088/1674-1056/27/7/077103
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The structural, anisotropic elastic properties and the ideal compressive and tensile strengths of titanium diboride (TiB2) were investigated using first-principles calculations based on density functional theory. The stress-strain relationships of TiB2 under <1010>, <1210>, and <0001> compressive loads were calculated. Our results showed that the ideal uniaxial compressive strengths are |σ<1210>|=142.96 GPa,|σ<0001>|=188.75 GPa, and |σ<1010>|=245.33 GPa, at strains-0.16,-0.32, and-0.24, respectively. The variational trend is just the opposite to that of the ideal tensile strength with σ<1010>=44.13 GPa, σ<0001>=47.03 GPa, and σ<1210>=56.09 GPa, at strains 0.14, 0.28, and 0.22, respectively. Furthermore, it was found that TiB2 is much stronger under compression than in tension. The ratios of the ideal compressive to tensile strengths are 5.56, 2.55, and 4.01 for crystallographic directions <1010>, <1210>, and <0001>, respectively. The present results are in excellent agreement with the most recent experimental data and should be helpful to the understanding of the compressive property of TiB2.

The effects of combining alloying elements on the elastic properties of γ-Ni in Ni-based superalloy: High-throughput first-principles calculations

Baokun Lu, Chongyu Wang
Chin. Phys. B 2018, 27 (7): 077104;  doi: 10.1088/1674-1056/27/7/077104
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Using high-throughput first-principles calculations, we systematically studied the synergistic effect of alloying two elements (Al and 28 kinds of 3d, 4d, and 5d transition metals) on the elastic constants and elastic moduli of γ-Ni. We used machine learning to theoretically predict the relationship between alloying concentration and mechanical properties, giving the binding energy between the two elements. We found that the ternary alloying elements strengthened the γ phase in the order of Re > Ir > W > Ru > Cr > Mo > Pt > Ta > Co. There is a quadratic parabolic relationship between the number of d shell electrons in the alloying element and the bulk modulus, and the maximum bulk modulus appears when the d shell is half full. We found a linear relationship between bulk modulus and alloying concentration over a certain alloying range. Using linear regression, we found the linear fit concentration coefficient of 29 elements. Using machine learning to theoretically predict the bulk modulus and lattice constants of Ni32XY, we predicted values close to the calculated results, with a regression parameter of R2=0.99626. Compared with pure Ni, the alloyed Ni has higher bulk modulus B, G, E, C11, and C44, but equal C12. The alloying strengthening in some of these systems is closely tied to the binding of elements, indicating that the binding energy of the alloy is a way to assess its elastic properties.

Mid-infrared luminescence of Dy3+-doped Ga2S3-Sb2S3-CsI chalcohalide glasses

Anping Yang, Jiahua Qiu, Mingjie Zhang, Mingyang Sun, Zhiyong Yang
Chin. Phys. B 2018, 27 (7): 077105;  doi: 10.1088/1674-1056/27/7/077105
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The mid-infrared (MIR) luminescent properties of Dy3+ ions in a new chalcohalide glass host, Ga2S3-Sb2S3-CsI, are investigated; and the suitability of the doped glass for MIR fiber lasers is evaluated. The Dy3+-doped chalcohalide glasses exhibit good thermal stability and intense MIR emissions around 2.96 μ and 4.41 μm. These emissions show quantum efficiencies (η) as high as ~60%, and have relatively large stimulated emission cross sections (σem). The low phonon energy (~307 cm-1) of the host glass accounts for the intense MIR emissions, as well as the high η. These favorable thermal and emission properties make the Dy3+-doped Ga2S3-Sb2S3-CsI glasses promising materials for MIR fiber amplifiers or lasers.

Metal-to-insulator transition in two-dimensional ferromagnetic monolayer induced by substrate

Can Qi, Jun Hu
Chin. Phys. B 2018, 27 (7): 077106;  doi: 10.1088/1674-1056/27/7/077106
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Two-dimensional (2D) ferromagnetic (FM) materials have great potential for applications in next-generation spintronic devices. Since most 2D FM materials come from van der Waals crystals, stabilizing them on a certain substrate without killing the ferromagnetism is still a challenge. Through systematic first-principles calculations, we proposed a new family of 2D FM materials which combines TaX (X=S, Se or Te) monolayer and Al2O3(0001) substrate. The TaX monolayers provide magnetic states and the Al2O3(0001) substrate stabilizes the former. Interestingly, the Al2O3(0001) substrate leads to a metal-to-insulator transition in the TaX monolayers and induces a band gap up to 303 meV. Our study paves the way to explore promising 2D FM materials for practical applications in spintronics devices.

Electronic properties of silicene in BN/silicene van der Waals heterostructures

Ze-Bin Wu, Yu-Yang Zhang, Geng Li, Shixuan Du, Hong-Jun Gao
Chin. Phys. B 2018, 27 (7): 077302;  doi: 10.1088/1674-1056/27/7/077302
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Silicene is a promising 2D Dirac material as a building block for van der Waals heterostructures (vdWHs). Here we investigate the electronic properties of hexagonal boron nitride/silicene (BN/Si) vdWHs using first-principles calculations. We calculate the energy band structures of BN/Si/BN heterostructures with different rotation angles and find that the electronic properties of silicene are retained and protected robustly by the BN layers. In BN/Si/BN/Si/BN heterostructure, we find that the band structure near the Fermi energy is sensitive to the stacking configurations of the silicene layers due to interlayer coupling. The coupling is reduced by increasing the number of BN layers between the silicene layers and becomes negligible in BN/Si/(BN)3/Si/BN. In (BN)n/Si superlattices, the band structure undergoes a conversion from Dirac lines to Dirac points by increasing the number of BN layers between the silicene layers. Calculations of silicene sandwiched by other 2D materials reveal that silicene sandwiched by low-carbon-doped boron nitride or HfO2 is semiconducting.

Intrinsic charge transport behaviors in graphene-black phosphorus van der Waals heterojunction devices

Guo-Cai Wang, Liang-Mei Wu, Jia-Hao Yan, Zhang Zhou, Rui-Song Ma, Hai-Fang Yang, Jun-Jie Li, Chang-Zhi Gu, Li-Hong Bao, Shi-Xuan Du, Hong-Jun Gao
Chin. Phys. B 2018, 27 (7): 077303;  doi: 10.1088/1674-1056/27/7/077303
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Heterostructures from mechanically-assembled stacks of two-dimensional materials allow for versatile electronic device applications. Here, we demonstrate the intrinsic charge transport behaviors in graphene-black phosphorus heterojunction devices under different charge carrier densities and temperature regimes. At high carrier densities or in the ON state, tunneling through the Schottky barrier at the interface between graphene and black phosphorus dominates at low temperatures. With temperature increasing, the Schottky barrier at the interface is vanishing, and the channel current starts to decrease with increasing temperature, behaving like a metal. While at low carrier densities or in the OFF state, thermal emission over the Schottky barrier at the interface dominates the carriers transport process. A barrier height of ~67.3 meV can be extracted from the thermal emission-diffusion theory.

Improving compatibility between thermoelectric components through current refraction

K Song, H P Song, C F Gao
Chin. Phys. B 2018, 27 (7): 077304;  doi: 10.1088/1674-1056/27/7/077304
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It is well known that components with dissimilar compatibility factors cannot be combined by segmentation into an efficient thermoelectric generator, since each component needs a unique optimal current density. Based on the complex variable method, the thermal-electric field within a bi-layered thermoelectric composite has been analyzed, and the field distributions have been obtained in closed-form. Our analysis shows that current refraction occurs at the interface, both the refraction angle and current density vary with the incidence angle. Further analysis proves that the current densities in two components can be adjusted independently by adjusting the incidence current density and incidence angle, thus the optimal current density can be matched in both components, and the conversion efficiency can be significantly increased. These results point to a new route for high efficiency thermoelectric composites.

Effect of Mn substitution on superconductivity in iron selenide (Li, Fe)OHFeSe single crystals

Yiyuan Mao, Zian Li, Huaxue Zhou, Mingwei Ma, Ke Chai, Shunli Ni, Shaobo Liu, Jinpeng Tian, Yulong Huang, Jie Yuan, Fang Zhou, Jianqi Li, Kui Jin, Xiaoli Dong, Zhongxian Zhao
Chin. Phys. B 2018, 27 (7): 077405;  doi: 10.1088/1674-1056/27/7/077405
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We synthesize a series of Mn substituted (Li, Fe)OHFeSe superconductor single crystals via a modified ion-exchange method, with the Mn concentration z (the atomic ratio of Mn:Se) ranging from 0 to 0.07. The distribution homogeneity of the Mn element incorporated into the lattice of (Li, Fe)OHFeSe is checked by combined measurements of high-angle-annular-dark-field (HAADF) imaging and electron energy-loss spectroscopy (EELS). Interestingly, we find that the superconducting transition temperature Tc and unit cell parameter c of the Mn-doped (Li, Fe)OHFeSe samples display similar V-shaped evolutions with the increasing dopant concentration z. We propose that, with increasing doping level, the Mn dopant first occupies the tetrahedral sites in the (Li, Fe)OH layers before starting to substitute the Fe element in the superconducting FeSe layers, which accounts for the V-shaped change in cell parameter c. The observed positive correlation between the Tc and lattice parameter c, regardless of the Mn doping level z, indicates that a larger interlayer separation, or a weaker interlayer coupling, is essential for the high-Tc superconductivity in (Li, Fe)OHFeSe. This agrees with our previous observations on powder, single crystal, and film samples of (Li, Fe)OHFeSe superconductors.

Highly sensitive and stable SERS probes of alternately deposited Ag and Au layers on 3D SiO2 nanogrids for detection of trace mercury ions

Yi Tian, Han-Fu Wang, Lan-Qin Yan, Xian-Feng Zhang, Attia Falak, Pei-Pei Chen, Feng-Liang Dong, Lian-Feng Sun, Wei-Guo Chu
Chin. Phys. B 2018, 27 (7): 077406;  doi: 10.1088/1674-1056/27/7/077406
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The hazard of Hg ion pollution triggers the motivation to explore a fast, sensitive, and reliable detection method. Here, we design and fabricate novel 36-nm-thick Ag-Au composite layers alternately deposited on three-dimensional (3D) periodic SiO2 nanogrids as surface-enhanced Raman scattering (SERS) probes. The SERS effects of the probes depend mainly on the positions and intensities of their localized surface plasmon resonance (LSPR) peaks, which is confirmed by the absorption spectra from finite-difference time-domain (FDTD) calculations. By optimizing the structure and material to maximize the intrinsic electric field enhancement based on the design method of 3D periodic SERS probes proposed, high performance of the Ag-Au/SiO2 nanogrid probes is achieved with the stability further enhanced by annealing. The optimized probes show the outstanding stability with only 4.0% SERS intensity change during 10-day storage, the excellent detection uniformity of 5.78% (RSD), the detection limit of 5.0×10-12 M (1 ppt), and superior selectivity for Hg ions. The present study renders it possible to realize the rapid and reliable detection of trace heavy metal ions by developing high-performance 3D periodic structure SERS probes by designing novel 3D structure and optimizing plasmonic material.

Asymmetric response of magnetic impurity in Bernal-stacked bilayer honeycomb lattice

Jin-Hua Sun, Ho-Kin Tang
Chin. Phys. B 2018, 27 (7): 077502;  doi: 10.1088/1674-1056/27/7/077502
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We utilize the Hirsch-Fye quantum Monte Carlo method to investigate the local moment formation of a magnetic impurity in a Bernal-stacked bilayer honeycomb lattice. A tight-binding model with the two most significant inter-layer hoppings, t1 between pairs of dimer sites and t3 between pairs of non-dimer sites, is used to describe the kinetic energy of the system. The local moment formed shows an asymmetric response to the inter-layer hoppings depending on which sublattice the impurity is coupled to. In the dimer and non-dimer couplings, the effects of t1 and t3 onto the local moment are quite opposite. When tuning the local moment, this asymmetric response is observed in a wide parameter range. This asymmetric response is also discussed by the computations of spectral densities, as well as correlation functions between the magnetic impurity and the conduction electrons.

Magnetic properties of L10 FePt thin film influenced byrecoverable strains stemmed from the polarization of Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate

Li-Wang Liu, Cheng-Chao Hu, Ye-Chuan Xu, Hou-Bing Huang, Jiang-Wei Cao, Linyun Liang, Wei-Feng Rao
Chin. Phys. B 2018, 27 (7): 077503;  doi: 10.1088/1674-1056/27/7/077503
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The magnetic properties and magnetization reversible processes of L10 FePt (3 nm)/Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) heterostructure were investigated by using the phase field model. The simulation results show that the magnetic coercivities and magnetic domains evolution in the L10 FePt thin film are significantly influenced by the compressive strains stemming from the polarization of single crystal PMN-PT substrate under an applied electric field. It is found that the magnetic coercivities increase with increasing of the compressive strain. A large compressive strain is beneficial to aligning the magnetic moments along the out-of-plane direction and to the enhancement of perpendicular magnetic anisotropy. The variations of magnetic energy densities show that when compressive strains are different at the magnetization reversible processes, the magnetic anisotropy energies and the magnetic exchange energies firstly increase and then decrease, the negative demagnetization energy peaks appear at coercivities fields, and the magnetoelastic energies are invariable at large external magnetic field with the energy maximum appearing at coercivities fields. The variations of the magnetoelastic energies bring about the perpendicular magnetic anisotropy so that the magnetoelastic energy is lower at the large external magnetic fields, whereas the appearance of magnetoelastic energy peaks is due to the magnetization-altered direction from the normal direction of the plane of the L10 FePt thin film at coercivities fields.

Magnetic properties of misch-metal partially substituted Nd-Fe-B magnets sintered by dual alloy method

Jie-Fu Xiong, Rong-Xiang Shang, Yan-Li Liu, Xin Zhao, Wen-Liang Zuo, Feng-Xia Hu, Ji-Rong Sun, Tong-Yun Zhao, Ren-Jie Chen, Bao-Gen Shen
Chin. Phys. B 2018, 27 (7): 077504;  doi: 10.1088/1674-1056/27/7/077504
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The misch-metal (MM) partially substituted Nd-Fe-B sintered magnets were fabricated by the dual alloy method, and the crystal structure, microstructure, and magnetic properties were analyzed comprehensively. X-ray diffraction (XRD) reveals that the increasing content of the MM has an inconsiderable effect on the crystallographic alignment of the magnets. Grains of the two main phases are uniformly distributed, and slightly deteriorate on the grain boundary. Due to the diffusion between the adjacent grains, the MM substituted Nd-Fe-B magnets contain three types of components with different Ce/La concentrations. Moreover, the first-order reversal curve (FORC) diagram is introduced to analyze the magnetization reversal process, coercivity mechanism, and distribution of reversal field in magnetic samples. The analysis indicates that there are two major reversal components, corresponding to the two different main phases. The domain nucleation and growth are determined to be the leading mechanism in controlling the magnetization reversal processes of the magnets sintered by the dual alloy method.

Domain wall dynamics in magnetic nanotubes driven by an external magnetic field

Zai-Dong Li, Yue-Chuan Hu, Peng-Bin He, Lin-Lin Sun
Chin. Phys. B 2018, 27 (7): 077505;  doi: 10.1088/1674-1056/27/7/077505
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We use the Landau-Lifshitz-Gilbert equation to investigate field-driven domain wall propagation in magnetic nanotubes. We find that the distortion is maximum as the time becomes infinite and the exact rigid-body solutions are obtained analytically. We also find that the velocity increases with increasing the ratio of inner radius and outer radius. That is to say, we can accelerate domain wall motion not only by increasing the magnetic field, but also by reducing the thickness of the nanotubes.

Crystal growth, spectroscopic characteristics, and Judd-Ofelt analysis of Dy: Lu2O3 for yellow laser

Jiaojiao Shi, Bin Liu, Qingguo Wang, Huili Tang, Feng Wu, Dongzhen Li, Hengyu Zhao, Zhanshan Wang, Wen Deng, Xiaodong Xu, Jun Xu
Chin. Phys. B 2018, 27 (7): 077802;  doi: 10.1088/1674-1056/27/7/077802
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Dy:Lu2O3 was grown by the float-zone (Fz) method. According to the absorption spectrum, the Judd-Ofelt (JO) parameters Ω2, Ω4, and Ω6 were calculated to be 4.86×10-20 cm2, 2.02×10-20 cm2, and 1.76×10-20 cm2, respectively. The emission cross-section at 574 nm corresponding to the 4F9/26H13/2 transition was calculated to be 0.53×10-20 cm2. The yellow (4F9/26H13/2 transition) to blue (4F9/26H15/2 transition) intensity ratio ranges up to 12.9. The fluorescence lifetime of the 4F9/2 energy level was measured to be 112.1 μs. These results reveal that Dy:Lu2O3 is a promising material for use in yellow lasers.

Time-resolved shadowgraphs and morphology analyses of aluminum ablation with multiple femtosecond laser pulses

Zehua Wu, Nan Zhang, Xiaonong Zhu, Liqun An, Gangzhi Wang, Ming Tan
Chin. Phys. B 2018, 27 (7): 077901;  doi: 10.1088/1674-1056/27/7/077901
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Aluminum ablation by multiple femtosecond laser pulses is investigated via time-resolved shadowgraphs and scanning electron microscope (SEM) images of the ablation spot. The spatial distribution of the ejected material and the radius of the shock wave generated during the ablation are found to vary with the increase in the number of pulses. In the initial two pulses, nearly concentric and semicircular stripes within the shock wave front are observed, unlike in subsequent pulses. Ablation by multiple femtosecond pulses exhibits different characteristics compared with the case induced by single femtosecond pulse because of the changes to the aluminum target surface induced by the preceding pulses.

Optoelectronic properties of single-crystalline GaInAsSb quaternary alloy nanowires

Meng-Zi Li, Xin-Liang Chen, Hong-Lai Li, Xue-Hong Zhang, Zhao-Yang Qi, Xiao-Xia Wang, Peng Fan, Qing-Lin Zhang, Xiao-Li Zhu, Xiu-Juan Zhuang
Chin. Phys. B 2018, 27 (7): 078101;  doi: 10.1088/1674-1056/27/7/078101
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Bandgap engineering of semiconductor nanomaterials is critical for their applications in nanoelectronics, optoelectronics, and photonics. Here we report, for the first time, the growth of single-crystalline quaternary alloyed Ga0.75In0.25As0.49Sb0.51 nanowires via a chemical-vapor-deposition method. The synthesized nanowires have a uniform composition distribution along the growth direction, with a zinc-blende structure. In the photoluminescence investigation, these quaternary alloyed semiconductor nanowires show a strong band edge light emission at 1950 nm (0.636 eV). Photodetectors based on these alloy nanowires show a strong light response in the near-infrared region (980 nm) with the external quantum efficiency of 2.0×104% and the responsivity of 158 A/W. These novel near-infrared photodetectors may find promising applications in integrated infrared photodetection, information communication, and processing.

Silica encapsulated ZnO quantum dot-phosphor nanocomposites: Sol-gel preparation and white light-emitting device application

Ya-Chuan Liang, Kai-Kai Liu, Ying-Jie Lu, Qi Zhao, Chong-Xin Shan
Chin. Phys. B 2018, 27 (7): 078102;  doi: 10.1088/1674-1056/27/7/078102
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ZnO quantum dots (QDs) as an eco-friendly and low-cost material has bright fluorescence, which makes it promising material for healthy lighting and displaying. However, the low fluorescence efficiency and poor stability of ZnO QDs impede their applications in lighting application. In this work, silica encapsulated ZnO QD-phosphors nanocomposites (ZSPN) have been prepared through a sol-gel synthesis process, where yellow-emitting ZnO QDs and blue-emitting BaMgAl10O17:Eu2+ are employed as the luminescence cores and silica as link between two luminescence materials. Tunable photoluminescence of ZSPN and the white light emission have been achieved through changing mass ratio of both of ZnO QDs and commercial phosphors. The PLQY of the ZSPN can reach 63.7% and they can maintain high luminous intensity even the ambient temperature up to 110 ℃ and after 35 h of UV irradiation. In addition, they can keep stable for 40 days. By coating the ZSPN phosphors onto a ultraviolet chip, WLEDs with luminous efficiency of 73.6 lm/W and the color coordinate, correlated color temperature, and color rendering index can reach (0.32, 0.34), 5580 K, and 87, respectively, indicating the bright prospect of the ZSPN phosphors used in healthy lighting.

A high-performance rechargeable Li-O2 battery with quasi-solid-state electrolyte Hot!

Jia-Yue Peng, Jie Huang, Wen-Jun Li, Yi Wang, Xiqian Yu, Yongsheng Hu, Liquan Chen, Hong Li
Chin. Phys. B 2018, 27 (7): 078201;  doi: 10.1088/1674-1056/27/7/078201
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A novel transparent and soft quasi-solid-state electrolyte (QSSE) was proposed and fabricated, which consists of ionic liquid (PYR14TFSI) and nano-fumed silica. The QSSE demonstrates high ionic conductivity of 4.6×10-4 S/cm at room temperature and wide electrochemical stability window of over 5 V. The Li-O2 battery using such quasi-solid-state electrolyte exhibits a low charge-discharge overpotential at the first cycle and excellent long-term cyclability over 500 cycles.

The electric field and frequency responses of giant electrorheological fluids

Hanqing Zhao, Rong Shen, Kunquan Lu
Chin. Phys. B 2018, 27 (7): 078301;  doi: 10.1088/1674-1056/27/7/078301
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The giant electrorheological (ER) fluid is based on the principle of a polar molecule dominated electrorheological (PM-ER) effect. The response of the shear stress for PM-ER fluid in alternate electric fields with triangle/square wave forms for different frequencies has been studied. The results show that the shear stress cannot well follow the rapid change of electric field and the average shear stresses of PM-ER fluids decrease with the increasing frequency of the applied field due to the response decay of the shear stress on applied field. The behavior is quite different from that of traditional ER fluids. However, the average shear stress of PM-ER fluid in a square wave electric field of ±E at low frequency can keep at high value. The obtained knowledge must be helpful for the design and operation of PM-ER fluids in the applications.

Dependence of single event upsets sensitivity of low energy proton on test factors in 65 nm SRAM

Yin-Yong Luo, Feng-Qi Zhang, Xiao-Yu Pan, Hong-Xia Guo, Yuan-Ming Wang
Chin. Phys. B 2018, 27 (7): 078501;  doi: 10.1088/1674-1056/27/7/078501
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In order to accurately predict the single event upsets (SEU) rate of on-orbit proton, the influence of the proton energy distribution, incident angle, supply voltage, and test pattern on the height, width, and position of SEU peak of low energy protons (LEP) in 65 nm static random access memory (SRAM) are quantitatively evaluated and analyzed based on LEP testing data and Monte Carlo simulation. The results show that different initial proton energies used to degrade the beam energy will bring about the difference in the energy distribution of average proton energy at the surface and sensitive region of the device under test (DUT), which further leads to significant differences including the height of SEU peak and the threshold energy of SEU. Using the lowest initial proton energy is extremely important for SEU testing with low energy protons. The proton energy corresponding to the SEU peak shifts to higher average proton energies with the increase of the tilt angle, and the SEU peaks also increase significantly. The reduction of supply voltage lowers the critical charge of SEU, leading to the increase of LEP SEU cross section. For standard 6-transitor SRAM with bit-interleaving technology, SEU peak does not show clear dependence on three test patterns of logical checkerboard 55H, all “1”, and all “0”. It should be noted that all the SEUs in 65 nm SRAM are single cell upset in LEP testing due to proton's low linear energy transfer (LET) value.

Ge/Si heterojunction L-shape tunnel field-effect transistors with hetero-gate-dielectric

Cong Li, Zhi-Rui Yan, Yi-Qi Zhuang, Xiao-Long Zhao, Jia-Min Guo
Chin. Phys. B 2018, 27 (7): 078502;  doi: 10.1088/1674-1056/27/7/078502
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A Ge/Si heterojunction L-shaped tunnel field-effect transistor combined with hetero-gate-dielectric (GHL-TFET) is proposed and investigated by TCAD simulation. Current-voltage characteristics, energy-band diagrams, and the distribution of the band-to-band tunneling (BTBT) generation rate of GHL-TFET are analyzed. In addition, the effect of the vertical channel width on the ON-current is studied and the thickness of the gate dielectric is optimized for better suppression of ambipolar current. Moreover, analog/RF figure-of-merits of GHL-TFET are also investigated in terms of the cut-off frequency and gain bandwidth production. Simulation results indicate that the ON-current of GHL-TFET is increased by about three orders of magnitude compared with that of the conventional L-shaped TFET. Besides, the introduction of the hetero-gate-dielectric not only suppresses the ambipolar current effectively but also improves the analog/RF performance drastically. It is demonstrated that the maximum cut-off frequency of GHL-TFET is about 160 GHz, which is 20 times higher than that of the conventional L-shaped TFET.

Synthesis of thermally stable HfOxNy as gate dielectric for AlGaN/GaN heterostructure field-effect transistors

Tong Zhang, Taofei Pu, Tian Xie, Liuan Li, Yuyu Bu, Xiao Wang, Jin-Ping Ao
Chin. Phys. B 2018, 27 (7): 078503;  doi: 10.1088/1674-1056/27/7/078503
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In this paper, we adopted thermally stable HfOxNy as gate dielectric for TiN/HfOxNy/AlGaN/GaN heterostructure field-effect transistors (HFETs) application. It demonstrated that the surface morphologies, composition, and optical properties of the HfOxNy films were dependent on oxygen flow rate in the O2/N2/Ar mixture sputtering ambient. The obtained metal-oxide-semiconductor heterostructure field-effect transistors by depositing HfO2 and HfOxNy dielectric at different oxygen flow rates possessed a small hysteresis and a low leakage current. After post deposition annealing at 900 ℃, the device using HfOxNy dielectric operated normally with good pinch-off characteristics, while obvious degradation are observed for the HfO2 gated one at 600 ℃. This result shows that the HfOxNy dielectric is a promising candidate for the self-aligned gate process.

Treatable focal region modulated by double excitation signal superimposition to realize platform temperature distribution during transcranial brain tumor therapy with high-intensity focused ultrasound

Shi-Hui Chang, Rui Cao, Ya-Bin Zhang, Pei-Guo Wang, Shi-Jing Wu, Yu-Han Qian, Xi-Qi Jian
Chin. Phys. B 2018, 27 (7): 078701;  doi: 10.1088/1674-1056/27/7/078701
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Recently, the phase compensation technique has allowed the ultrasound to propagate through the skull and focus into the brain. However, the temperature evolution during treatment is hard to control to achieve effective treatment and avoid over-high temperature. Proposed in this paper is a method to modulate the temperature distribution in the focal region. It superimposes two signals which focus on two preset different targets with a certain distance. Then the temperature distribution is modulated by changing triggering time delay and amplitudes of the two signals. The simulation model is established based on an 82-element transducer and computed tomography (CT) data of a volunteer's head. A finite-difference time-domain (FDTD) method is used to calculate the temperature distributions. The results show that when the distances between the two targets respectively are 7.5-12.5 mm on the acoustic axis and 2.0-3.0 mm in the direction perpendicular to the acoustic axis, a focal region with a uniform temperature distribution (64-65 ℃) can be created. Moreover, the volume of the focal region formed by one irradiation can be adjusted (26.8-266.7 mm3) along with the uniform temperature distribution. This method may ensure the safety and efficacy of HIFU brain tumor therapy.

Dependence of the solar cell performance on nanocarbon/Si heterojunctions

Shiqi Xiao, Qingxia Fan, Xiaogang Xia, Zhuojian Xiao, Huiliang Chen, Wei Xi, Penghui Chen, Junjie Li, Yanchun Wang, Huaping Liu, Weiya Zhou
Chin. Phys. B 2018, 27 (7): 078801;  doi: 10.1088/1674-1056/27/7/078801
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Solar cells that combine single-crystalline silicon (Si) with graphene (G) have been widely researched in order to develop next-generation photovoltaic devices. However, the power conversion efficiency (PCE) of G/Si solar cell without chemical doping is commonly low due to the relatively high resistance of graphene. In this work, through combining graphene with carbon nanotube (CNT) networks, we fabricated three kinds of hybrid nanocarbon film/Si heterojunction solar cells in order to increase the PCE of the graphene based Si solar cell. We investigated the characteristics of different nanocarbon film/Si solar cells and found that their performance depends on the heterojunctions. Specifically, a doping-free G-CNT/Si solar cell demonstrated a high PCE of 7.9%, which is nearly equal to the combined value of two individuals (G/Si and CNT/Si). This high efficiency is attributed to the synergistic effect of graphene and CNTs, and can be further increased to 9.1% after applying a PMMA antireflection coating. This study provides a potential way to further improve the Si based heterojunction solar cells.

Self-assembled monolayer modified copper(I) iodide hole transport layer for efficient polymer solar cells

Yuancong Zhong, Qilun Zhang, You Wei, Qi Li, Yong Zhang
Chin. Phys. B 2018, 27 (7): 078802;  doi: 10.1088/1674-1056/27/7/078802
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The morphology of the copper iodide (CuI) film as an inorganic p-type material has an important influence on enhancing the performance of polymer solar cells (PSCs). A self-assembled monolayer of 3-aminopropanoic acid (C3-SAM) was used on the surface of indium tin oxide (ITO) before depositing the CuI films. Consequently, a well-distributed and smooth CuI film was formed with pinhole free and complete surface coverage. The root mean square of the corresponding CuI film was reduced from 3.63 nm for ITO/CuI to 0.77 nm. As a result, the average power conversion efficiency (PCE) of PSCs with the device structure of ITO/C3-SAM/CuI/P3HT:PC61BM/ZnO/Al increased significantly from 2.55% (best 2.66%) to 3.04% (best 3.20%) after C3-SAM treatment. This work provides an effective strategy to control the morphology of CuI films through interfacial modification and promotes its application in efficient PSCs.

Model and application of bidirectional pedestrian flows at signalized crosswalks

Tao Zhang, Gang Ren, Zhi-Gang Yu, Yang Yang
Chin. Phys. B 2018, 27 (7): 078901;  doi: 10.1088/1674-1056/27/7/078901
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This research of bidirectional pedestrian flows at signalized crosswalks is divided into two parts:model and application. In the model part, a mixed survey including the questionnaire investigation and tracking investigation is conducted to gain the basic data about walking tendentiousness of a pedestrian crossing. Then, the forward, right-hand, outstripping, and influential coefficients are outlined to quantize walking tendentiousness of pedestrian crossing and estimate transition probabilities of pedestrians. At last, an improved cellular automation model is proposed to describe walking tendentiousness and crossing behaviors of pedestrians. In the application part, channelization research of bidirectional pedestrian flows is presented for real signalized crosswalk. In this process, the effects of right-side-walking and conformity behaviors on the efficiency of pedestrian crossing are thoroughly analyzed based on simulations and experiments to obtain a final channelization method to raise the efficiency of a pedestrian crossing at the crosswalk.
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