#### Current Issue

Volume 34 Issue 8
Online Date:
GENERAL
 Select Validation of the Ability of Full Configuration Interaction Quantum Monte Carlo for Studying the 2D Hubbard Model Su-Jun Yun, Tie-Kuang Dong, Shi-Ning Zhu Chin. Phys. Lett. 2017, 34 (8): 080201 .   DOI: 10.1088/0256-307X/34/8/080201 Abstract   PDF(pc) (567KB) ( 483 ) PDF(mobile)(561KB) ( 47 ) HTML ( 56 )  To validate the ability of full configuration interaction quantum Monte Carlo (FCIQMC) for studying the 2D Hubbard model near half-filling regime, the ground state energies of a $4\times4$ square lattice system with various interaction strengths are calculated. It is found that the calculated results are in good agreement with those obtained by exact diagonalization (i.e., the exact values for a given basis set) when the population of psi particles (psips) is higher than the critical population required to correctly sample the ground state wave function. In addition, the variations of the average computational time per 20 Monte Carlo cycles with the coupling strength and the number of processors are also analyzed. The calculated results show that the computational efficiency of an FCIQMC calculation is mainly affected by the total population of psips and the communication between processors. These results can provide useful references for understanding the FCIQMC algorithm, studying the ground state properties of the 2D Hubbard model for the larger system size by the FCIQMC method and using a computational budget as effectively as possible.
 Select A Realization of the $W_{1+\infty}$ Algebra and Its $n$-Algebra Chun-Hong Zhang, Rui Wang, Ke Wu, Wei-Zhong Zhao Chin. Phys. Lett. 2017, 34 (8): 080202 .   DOI: 10.1088/0256-307X/34/8/080202 Abstract   PDF(pc) (514KB) ( 142 ) PDF(mobile)(511KB) ( 17 ) HTML ( 76 )  We consider a realization of the $W_{1+\infty}$ algebra and investigate its $n$-algebra, which is different from the $n$-algebra of Zhang et al. [2016 arXiv:1606.07570v2] It is found that the generators $W_m^{s}$ with any fixed superindex $s\geqslant 1$ yield the null sub-$2s$-algebra. The nontrivial sub-$4$-algebra and Virasoro–Witt $3$-algebra are presented. Moreover, we extend the generators to the multi-variables case. These generators also yield the $W_{1+\infty}$ algebra and null $n$-algebras.
 Select Asymmetric Decoy State Measurement-Device-Independent Quantum Cryptographic Conferencing Rui-Ke Chen, Wan-Su Bao, Hai-Ze Bao, Chun Zhou, Mu-Sheng Jiang, Hong-Wei Li Chin. Phys. Lett. 2017, 34 (8): 080301 .   DOI: 10.1088/0256-307X/34/8/080301 Abstract   PDF(pc) (558KB) ( 242 ) PDF(mobile)(552KB) ( 4 ) HTML ( 16 )  Measurement-device-independent quantum cryptographic conferencing (MDI-QCC) protocol suggests an important scheme for practical multiparty quantum communication. As far as we know, MDI-QCC or MDI-quantum key distribution protocols always assume that the decoy state strategies used at each user's side are the same. In this study, to mitigate the system complexity and to improve the performance of MDI-QCC protocol in the finite-key case, we propose an asymmetric decoy state method for MDI-QCC protocol, and present security analysis and numerical simulations. From numerical simulations, our protocol can achieve better performance in the finite-key case. That is, with a finite data size of $10^{11}$, it can achieve nonzero secret key rate over 43.6 km.
 Select Application of a Discrete Phase-Randomized Coherent State Source in Round-Robin Differential Phase-Shift Quantum Key Distribution Ying-Ying Zhang, Wan-Su Bao, Hong-Wei Li, Chun Zhou, Yang Wang, Mu-Sheng Jiang Chin. Phys. Lett. 2017, 34 (8): 080302 .   DOI: 10.1088/0256-307X/34/8/080302 Abstract   PDF(pc) (534KB) ( 226 ) PDF(mobile)(531KB) ( 14 ) HTML ( 9 )  Recently, a novel kind of quantum key distribution called the round-robin differential phase-shift (RRDPS) protocol was proposed, which bounds the amount of leakage without monitoring signal disturbance. The protocol can be implemented by a weak coherent source. The security of this protocol with a simply characterized source has been proved. The application of a common phase shift can improve the secret key rate of the protocol. In practice, the randomized phase is discrete and the secret key rate is deviated from the continuous case. In this study, we analyze security of the RRDPS protocol with discrete-phase-randomized coherent state source and bound the secret key rate. We fix the length of each packet at 32 and 64, then simulate the secret key rates of the RRDPS protocol with discrete-phase randomization and continuous-phase randomization. Our simulation results show that the performance of the discrete-phase randomization case is close to the continuous counterpart with only a small number of discrete phases. The research is practically valuable for experimental implementation.
 Select Energy and Thermodynamics of the Quantum-Corrected Schwarzschild Black Hole Mahamat Saleh, Bouetou Bouetou Thomas, Timoleon Crepin Kofane Chin. Phys. Lett. 2017, 34 (8): 080401 .   DOI: 10.1088/0256-307X/34/8/080401 Abstract   PDF(pc) (488KB) ( 326 ) PDF(mobile)(476KB) ( 12 ) HTML ( 10 )  Energy and thermodynamics are investigated in the Schwarzschild black hole spacetime when considering corrections due to quantum vacuum fluctuations. The Einstein and Møller prescriptions are used to derive the expressions of the energy in the background. The temperature and heat capacity are also derived. The results show that due to the quantum fluctuations in the background of the Schwarzschild black hole, all the energies increase and the Einstein energy differs from Møller's one. Moreover, when increasing the quantum correction factor $a$, the difference between Einstein and Møller energies, the Unruh–Verlinde temperature as well as the heat capacity of the black hole increases while the Hawking temperature remains unchanged.
 Select The $P$–$v$ Criticality of a Noncommutative Geometry-Inspired Schwarzschild-AdS Black Hole Jun Liang Chin. Phys. Lett. 2017, 34 (8): 080402 .   DOI: 10.1088/0256-307X/34/8/080402 Abstract   PDF(pc) (521KB) ( 217 ) PDF(mobile)(510KB) ( 5 ) HTML ( 6 )  The $P$–$v$ criticality and phase transition in the extended phase space of a noncommutative geometry-inspired Schwarzschild black hole in anti-de Sitter (AdS) spacetime are studied. The cosmological constant is treated as a dynamical pressure and its conjugate quantity is thermodynamic volume of the noncommutative geometry-inspired Schwarzschild-AdS black hole. The noncommutative parameter is also treated as a variable, and as a consequence, a new thermodynamic quantity $V_{\theta}$ conjugate to $P_{\theta}=-(8\pi \theta)^{-1}$ has to be defined further, which is required for consistency of both the first law of thermodynamics and the corresponding Smarr relation. We find that the $P$–$v$ criticality and the small black hole/large black hole phase transition appear for the noncommutative Schwarzschild-AdS black hole. Numerical calculations indicate that the noncommutative parameter $\theta$ affects the phase transition as well as the critical temperature $T_{\rm c}$, horizon radius $r_{\rm +c}$ and pressure $P_{\rm c}$. However, the critical ratio $P_{\rm c}r_{\rm +c}/T_{\rm c}$ is universal (independent of $\theta$), which is very similar to the result in the van de Waals liquid–gas system, but different from that in the noncommutative geometry-inspired Reissner–Nordström-AdS black hole, where the critical ratio is no longer universal.
 Select Bifurcation Analysis and Transition Mechanism in a Modified Model of Ca$^{2+}$ Oscillations Quan-Bao Ji, Zhuo-Qin Yang, Fang Han Chin. Phys. Lett. 2017, 34 (8): 080501 .   DOI: 10.1088/0256-307X/34/8/080501 Abstract   PDF(pc) (610KB) ( 244 ) PDF(mobile)(607KB) ( 11 ) HTML ( 6 )  Some new elements are introduced into a mathematical model of intracellular calcium oscillations, which make it particularly suitable for the study of bifurcation. In addition to generating regular oscillations, such a modified model can be used to reproduce the burst discharges similar to those recorded in experiments and to describe two new types of oscillatory phenomena. By means of a fast/slow dynamical analysis, we explore the bifurcation and transition mechanisms associated with two types of bursters due to changes in the interaction of two slow variables with different timescales.
 Select Progress of the Inertial Mass Measurement Project at NIM Zhuang Fu, Zhong-Hua Zhang, Zheng-Kun Li, Wei Zhao, Lu-Shuai Qian, Shi-Song Li Chin. Phys. Lett. 2017, 34 (8): 080601 .   DOI: 10.1088/0256-307X/34/8/080601 Abstract   PDF(pc) (638KB) ( 229 ) PDF(mobile)(635KB) ( 13 ) HTML ( 0 )  An experiment is proposed to precisely measure the Planck constant. In this experiment, the Planck constant is measured based on the inertial mass measurement rather than the gravitational mass determinations in some other well-known experiments, e.g., the Kibble balance and counting atoms. We link the mechanical force to a quantum-traceable electrostatic force by a beam balance oscillator. After a 5-year continuous effort, the principle of the proposal is verified by a preliminary measurement with a relative uncertainty of $5.4\times 10^{-5}$. The proposal has the potential to achieve much higher measurement accuracy with further improvements.
NUCLEAR PHYSICS
 Select Pygmy and Giant Dipole Resonances in Proton-Rich Nuclei $^{17,18}$Ne Hong Lv, Shi-Sheng Zhang, Zhen-Hua Zhang, Yu-Qian Wu, Li-Gang Cao Chin. Phys. Lett. 2017, 34 (8): 082101 .   DOI: 10.1088/0256-307X/34/8/082101 Abstract   PDF(pc) (611KB) ( 237 ) PDF(mobile)(598KB) ( 6 ) HTML ( 6 )  The pygmy and giant dipole resonances in proton-rich nuclei $^{17,18}$Ne are investigated with a fully self-consistent approach. The properties of ground states are calculated in the Skyrme Hartree–Fock with the Bardeen–Cooper–Schrieffer approximation to take into account the pairing correlation. The quasiparticle random phase approximation (QRPA) method is used to explore the properties of excited dipole states. In the calculations the SLy5 Skyrme interaction is employed. In addition to the giant dipole resonances, pygmy dipole resonances (PDR) are found to be located in the energy region below 10 MeV in both $^{17,18}$Ne. The strength and transition density show that the low-lying states are typical PDR states. However, analyzing the QRPA amplitudes of proton and neutron 2 quasiparticle (2qp) configurations for a given low-lying state in $^{17,18}$Ne, we find that the PDR state is less collective, more like a single 2qp excitation.
ATOMIC AND MOLECULAR PHYSICS
 Select Coherent Features of Resonance-Mediated Two-Photon Absorption Enhancement by Varying the Energy Level Structure, Laser Spectrum Bandwidth and Central Frequency Wen-Jing Cheng, Guo Liang, Ping Wu, Tian-Qing Jia, Zhen-Rong Sun, Shi-An Zhang Chin. Phys. Lett. 2017, 34 (8): 083201 .   DOI: 10.1088/0256-307X/34/8/083201 Abstract   PDF(pc) (760KB) ( 179 ) PDF(mobile)(760KB) ( 3 ) HTML ( 8 )  The femtosecond pulse shaping technique has been shown to be an effective method to control the multi-photon absorption by the light–matter interaction. Previous studies mainly focused on the quantum coherent control of the multi-photon absorption by the phase, amplitude and polarization modulation, but the coherent features of the multi-photon absorption depending on the energy level structure, the laser spectrum bandwidth and laser central frequency still lack in-depth systematic research. In this work, we further explore the coherent features of the resonance-mediated two-photon absorption in a rubidium atom by varying the energy level structure, spectrum bandwidth and central frequency of the femtosecond laser field. The theoretical results show that the change of the intermediate state detuning can effectively influence the enhancement of the near-resonant part, which further affects the transform-limited (TL)-normalized final state population maximum. Moreover, as the laser spectrum bandwidth increases, the TL-normalized final state population maximum can be effectively enhanced due to the increase of the enhancement in the near-resonant part, but the TL-normalized final state population maximum is constant by varying the laser central frequency. These studies can provide a clear physical picture for understanding the coherent features of the resonance-mediated two-photon absorption, and can also provide a theoretical guidance for the future applications.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
 Select Carpet Cloak Design for Rough Surfaces Mohammad Hosein Fakheri, Hooman Barati, Ali Abdolali Chin. Phys. Lett. 2017, 34 (8): 084101 .   DOI: 10.1088/0256-307X/34/8/084101 Abstract   PDF(pc) (2276KB) ( 306 ) PDF(mobile)(2276KB) ( 8 ) HTML ( 12 )  Conventional carpet cloak structures have been utilized to conceal the objects located on a planar perfect electric conductor surface. We systematically investigate hiding arbitrarily shaped objects on a rough surface, as a more general and practical scenario. In addition, the required cloak is designed considering different boundary conditions for the surface beneath the object, despite the previous studies. To achieve an invisibility cloak, taking advantage of linear coordinate transformation, a simple homogeneous material is obtained to realize the cloak structure, facilitating the fabrication processes. Numerical simulations validate the performance of the proposed cloaking method. Therefore, the proposed structure is capable of cloaking in more general and complicated scenarios.
 Select Controlling of the Polarization States of Electromagnetic Waves Using Epsilon-near-Zero Metamaterials Xiao-Jing Zhang, Xi Wu, Ya-Dong Xu Chin. Phys. Lett. 2017, 34 (8): 084102 .   DOI: 10.1088/0256-307X/34/8/084102 Abstract   PDF(pc) (712KB) ( 285 ) PDF(mobile)(706KB) ( 10 ) HTML ( 2 )  We demonstrate theoretically that the epsilon-near-zero materials can be utilized to control effectively the polarization conversion of an electromagnetic wave through reflection. The significant feature differing from all other means based on whatever natural materials or metamaterials is that for TM incident wave, the reflected phase is a constant, while for TE wave, the reflected phase is a linear function of the incident angle. The phase difference between them covers the range from $-$180${^\circ}$ to 0${^\circ}$, and the polarization conversions from linear states to elliptical or circular states can be obtained by only adjusting the incident angle. Because no complex structures are employed, our proposal promises a simple approach for manipulating polarization conversion at both terahertz and optical frequencies.
 Select Pressure Dependence of the Small-Signal Gain and Saturation Intensity of a Copper Bromide Laser M. E. Aeinehvand, S. Behrouzinia, M. K. Salem, M. Elahei, K. Khorasani Chin. Phys. Lett. 2017, 34 (8): 084201 .   DOI: 10.1088/0256-307X/34/8/084201 Abstract   PDF(pc) (496KB) ( 185 ) PDF(mobile)(496KB) ( 2 ) HTML ( 6 )  A pair of copper bromide lasers in an oscillator–amplifier configuration is used to investigate the small signal gain and saturation intensity as amplifying parameters and output power of lasers, versus pressure of buffer gas. It is shown that the amplifying parameters and laser output power have a maximum value at optimum buffer gas pressure of 11 Torr. The challenge between microscopic parameters such as stimulated emission cross section, laser upper level lifetime, and population inversion, which determine the values of laser characteristics respective to the operational pressure of buffer gas, are investigated. Thus an optimum delay time of about 10 ns is determined, and a maximum output power equivalent to about 12 W is extracted. The amplifying parameters and measured output power of laser versus delay times show some local maxima and minima at the delay time interval of 6–43 ns.
 Select High-Power Single-Spatial-Mode GaSb Tapered Laser around 2.0μm with Very Small Lateral Beam Divergence Shu-Shan Huang, Yu Zhang, Yong-Ping Liao, Cheng-Ao Yang, Xiao-Li Chai, Ying-Qiang Xu, Hai-Qiao Ni, Zhi-Chuan Niu Chin. Phys. Lett. 2017, 34 (8): 084202 .   DOI: 10.1088/0256-307X/34/8/084202 Abstract   PDF(pc) (783KB) ( 223 ) PDF(mobile)(779KB) ( 2 ) HTML ( 5 )  We report high-power single-spatial-mode type-I GaSb-based tapered lasers fabricated on the InGaSb/AlGaAsSb material system. A straight ridge and three different tapered waveguide structures with varying flare angles are fabricated to optimize the output power and spatial-mode performance. The best devices exhibit single-spatial-mode operation with room-temperature output power up to 350 mW in continuous-wave mode at an emission wavelength around 2.0 μm with a very small far-field lateral divergence angle, which is beyond state of the art in terms of single-spatial-mode output power.
 Select Erbium-Doped Zirconia-Alumina Silica Glass-Based Fiber as a Saturable Absorber for High Repetition Rate Q-Switched All-Fiber Laser Generation P. Harshavardhan Reddy, N. A. A. Kadir, M. C. Paul, S. Das, A. Dhar, E. I. Ismail, A. A. Latiff, S. W. Harun Chin. Phys. Lett. 2017, 34 (8): 084203 .   DOI: 10.1088/0256-307X/34/8/084203 Abstract   PDF(pc) (2477KB) ( 831 ) PDF(mobile)(2473KB) ( 4 ) HTML ( 0 )  We propose and demonstrate a Q-switched erbium-doped fiber laser (EDFL) using an erbium-doped zirconia-alumina silica glass-based fiber (Zr-EDF) as a saturable absorber. As a 16-cm-long Zr-EDF is incorporated into a ring EDFL cavity, a stable Q-switching pulse train operating at 1565 nm wavelength is successfully obtained. The repetition rate is tunable from 33.97 kHz to 71.23 kHz by increasing the pump power from the threshold of 26 mW to the maximum of 74 mW. The highest pulse energy of 26.67 nJ is obtained at the maximum pump power.
 Select Wideband Tunable Frequency-Doubling Optoelectronic Oscillator Using a Polarization Modulator and an Optical Bandpass Filter Qing-Chao Huang, Qi Wang, Cheng-Wu Yang, Wei Chen, Jian-Guo Liu, Ning-Hua Zhu Chin. Phys. Lett. 2017, 34 (8): 084204 .   DOI: 10.1088/0256-307X/34/8/084204 Abstract   PDF(pc) (622KB) ( 379 ) PDF(mobile)(615KB) ( 1 ) HTML ( 2 )  A wideband tunable frequency-doubling optoelectronic oscillator (FD-OEO) is proposed and experimentally demonstrated based on a polarization modulator and an optical bandpass filter (OBPF). The central frequency of the correspondingly fundamental OEO could be adjusted by tuning the bandwidth and central frequency of the OBPF, which could also be regarded as a photonic-assisted tunable microwave filter. The frequency tuning range of the FD-OEO covers from 9.5 to 32.8 GHz, and the single sideband phase noise of the fundamental signal is lower than $-$100 dBc/Hz at an offset of 10 kHz. Moreover, the frequency stability of the generated signal is investigated by measuring its Allan deviation. The Allan deviation of the generated fundamental signal at 10 GHz is 2.39$\times$10$^{-9}$.
 Select Bistability in a Hybrid Optomechanical System under the Effect of a Nonlinear Medium A. Asghari Nejad, H. R. Askari, H. R. Baghshahi Chin. Phys. Lett. 2017, 34 (8): 084205 .   DOI: 10.1088/0256-307X/34/8/084205 Abstract   PDF(pc) (668KB) ( 341 ) PDF(mobile)(663KB) ( 1 ) HTML ( 2 )  We investigate a hybrid optomechanical system consisting of two coupled cavities, one of them is composed of two-end fixed mirrors (called the traditional cavity), and the other has a one-end oscillating mirror (named as the optomechanical cavity). A Kerr medium is inside the traditional cavity to enhance the nonlinearity due to the fact that it can cause observing of bistable behavior in intracavity intensity for the optomechanical cavity. The Hamiltonian of the system is written in a rotating frame and its dynamics is described by quantum Langevin equations of motion. Our proposed system exhibits unconventional plots for the mean photon number of the optomechanical cavity which are not observed in previous works. The present results show a deep effect of the Kerr medium on optical bistability of intracavity intensity for the optomechanical cavity. Also, coupling strength of the cavities can effectively change the stability of the system.
 Select Terahertz Three-Dimensional Imaging Based on Computed Tomography with Photonics-Based Noise Source Tao Zhou, Rong Zhang, Chen Yao, Zhang-Long Fu, Di-Xiang Shao, Jun-Cheng Cao Chin. Phys. Lett. 2017, 34 (8): 084206 .   DOI: 10.1088/0256-307X/34/8/084206 Abstract   PDF(pc) (758KB) ( 222 ) PDF(mobile)(756KB) ( 2 ) HTML ( 5 )  Computed tomography has been proven to be useful for non-destructive inspection of structures and materials. We build a three-dimensional imaging system with the photonically generated incoherent noise source and the Schottky barrier diode detector in the terahertz frequency band (90–140 GHz). Based on the computed tomography technique, the three-dimensional image of a ceramic sample is reconstructed successfully by stacking the slices at different heights. The imaging results not only indicate the ability of terahertz wave in the non-invasive sensing and non-destructive inspection applications, but also prove the effectiveness and superiority of the uni-traveling-carrier photodiode as a terahertz source in the imaging applications.
 Select Two-Dimensional Talbot Effect with Atomic Density Gratings Chen Li, Tian-Wei Zhou, Jing-Gang Xiang, Yue-Yang Zhai, Xu-Guang Yue, Shi-Feng Yang, Wei Xiong, Xu-Zong Chen Chin. Phys. Lett. 2017, 34 (8): 084207 .   DOI: 10.1088/0256-307X/34/8/084207 Abstract   PDF(pc) (837KB) ( 285 ) PDF(mobile)(836KB) ( 2 ) HTML ( 0 )  We report the experimental observation of two-dimensional Talbot effect when a resonance plane wave interacts with a two-dimensional atomic density grating generated by standing wave manipulation of ultracold Bose gases. Clear self-images of the grating and sub-images with reversed phase or fractal patterns are observed. By calculating the autocorrelation functions of the images, the behavior of periodic Talbot images is studied. The Talbot effect with two-dimensional atomic density grating expands the applications of the Talbot effect in a wide variety of research fields.
 Select Cavitation Bubble Collapse near a Curved Wall by the Multiple-Relaxation-Time Shan–Chen Lattice Boltzmann Model Hong-Hui Xue, Feng Shan, Xia-Sheng Guo, Juan Tu, Dong Zhang Chin. Phys. Lett. 2017, 34 (8): 084301 .   DOI: 10.1088/0256-307X/34/8/084301 Abstract   PDF(pc) (789KB) ( 328 ) PDF(mobile)(786KB) ( 0 ) HTML ( 3 )  The cavitation bubble collapse near a cell can cause damage to the cell wall. This effect has received increasing attention in biomedical supersonics. Based on the lattice Boltzmann method, a multiple-relaxation-time Shan–Chen model is built to study the cavitation bubble collapse. Using this model, the cavitation phenomena induced by density perturbation are simulated to obtain the coexistence densities at certain temperature and to demonstrate the Young–Laplace equation. Then, the cavitation bubble collapse near a curved rigid wall and the consequent high-speed jet towards the wall are simulated. Moreover, the influences of initial pressure difference and bubble-wall distance on the cavitation bubble collapse are investigated.
 Select A Theoretical Model for the Asymmetric Transmission of Powerful Acoustic Wave in Double-Layer Liquids Xun Wang, Wei-Zhong Chen, Qi Wang, Jin-Fu Liang Chin. Phys. Lett. 2017, 34 (8): 084302 .   DOI: 10.1088/0256-307X/34/8/084302 Abstract   PDF(pc) (691KB) ( 193 ) PDF(mobile)(682KB) ( 14 ) HTML ( 6 )  A theoretical model which couples the oscillation of cavitation bubbles with the equation of an acoustic wave is utilized to describe the sound fields in double-layer liquids, which can be used to realize the asymmetric transmission of acoustic waves. Numerical simulations show that the asymmetry is related to the properties of the host liquids and the input acoustic wave. Asymmetry can be enhanced if the maximum number density or the ambient radius of the cavitation bubbles in the low cavitation threshold liquid increases. Moreover, the direction of rectification will be reversed if the amplitude of the input acoustic wave becomes high enough.
 Select Rear-Surface Deformation of a Water Drop in Aero-Breakup of Shear Mode Xiang-Yu Yi, Yu-Jian Zhu, Ji-Ming Yang, Tun Wang, Ming-Yu Sun Chin. Phys. Lett. 2017, 34 (8): 084701 .   DOI: 10.1088/0256-307X/34/8/084701 Abstract   PDF(pc) (1990KB) ( 859 ) PDF(mobile)(1990KB) ( 2 ) HTML ( 2 )  Deformation of water drops in shock-induced high-speed flows is investigated with a focus to the influence of primitive flow parameters on the rear-surface deformation features. Two typical deformation patterns are discovered through high-speed photography. A simple equation to evaluate the radial acceleration of the drop surface is derived. The combined use of this equation and outer flow simulation makes it possible for us to reconstruct the profiles of the early deformed drops. The results agree well with the experiments. Further analysis shows that the duration of flow establishment with respect to the overall breakup time shapes the rear side profile of the drop. Thereby the ratio of the two times, expressed as the square root of the density ratio, appears to be an effective indicator of the deformation features.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
 Select High-Yield High-Efficiency Positron Generation in High-$Z$ Metal Targets Irradiated by Laser Produced Electrons from Near-Critical Density Plasmas Wei Song, Rong-Hao Hu, Yin-Ren Shou, Zheng Gong, Jin-Qing Yu, Chen Lin, Wen-Jun Ma, Yan-Yin Zhao, Hai-Yang Lu, Xue-Qing Yan Chin. Phys. Lett. 2017, 34 (8): 085201 .   DOI: 10.1088/0256-307X/34/8/085201 Abstract   PDF(pc) (978KB) ( 267 ) PDF(mobile)(972KB) ( 3 ) HTML ( 4 )  An improved indirect scheme for laser positron generation is proposed. The positron yields in high-$Z$ metal targets irradiated by laser produced electrons from near-critical density plasmas and underdense plasma are investigated numerically. It is found that the positron yield is mainly affected by the number of electrons of energies up to several hundreds of MeV. Using near-critical density targets for electron acceleration, the number of high energy electrons can be increased dramatically. Through start-to-end simulations, it is shown that up to $6.78\times10^{10}$ positrons can be generated with state-of-the-art Joule-class femtosecond laser systems.
 Select The Diffusion Coefficient Using Sawtooth Oscillation in IR-T1 Tokamak N. Hasanvand, S. Meshkani, M. Ghoranneviss Chin. Phys. Lett. 2017, 34 (8): 085202 .   DOI: 10.1088/0256-307X/34/8/085202 Abstract   PDF(pc) (596KB) ( 206 ) PDF(mobile)(596KB) ( 1 ) HTML ( 3 )  The investigation of runaway electrons is expanded by different methods. The aim of this study is to show sawtooth oscillations of hard x-ray emission and with the help of sawtooth oscillations to obtain radial diffusion coefficient and magnetic fluctuations. In the same way, the hard x-ray spectral evaluation is compared in several time intervals and it is shown that during discharge, the energy of the runaway electrons is less than 200 keV. Also, for typical plasmas, population of runaway electrons is measured at seven time intervals of 5 ms and temporal evaluation of runaway electron mean energy. The sawtooth-like shape is observed in the hard x-ray range (10–1000 keV). By the sawtooth oscillation method, the RE diffusion coefficient in radial transport in the IR-T1 plasma is $D_{\rm r}\sim 0.5$ m$^2$s$^{-1}$. The magnetic field fluctuation due to magnetic diffusion $D_{\rm m}$ is given as $\frac{b_{\rm r}}{B_{\rm t}}\sim 10^{-4}$.
 Select A Method of Using a Carbon Fiber Spiral-Contact Electrode to Achieve Atmospheric Pressure Glow Discharge in Air Wen-Zheng Liu, Shuai Zhao, Mao-Lin Chai, Jiang-Qi Niu Chin. Phys. Lett. 2017, 34 (8): 085203 .   DOI: 10.1088/0256-307X/34/8/085203 Abstract   PDF(pc) (1037KB) ( 196 ) PDF(mobile)(1036KB) ( 2 ) HTML ( 4 )  During discharge, appropriately changing the development paths of electron avalanches and increasing the number of initial electrons can effectively inhibit the formation of filamentary discharge. Based on the aforementioned phenomenon, we propose a method of using microdischarge electrodes to produce a macroscopic discharge phenomenon. In the form of an asymmetric structure composed of a carbon fiber electrode, an electrode structure of carbon fiber spiral-contact type is designed to achieve an atmospheric pressure glow discharge in air, which is characterized by low discharge voltage, low energy consumption, good diffusion and less ozone generation.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
 Select Charge Density Wave States and Structural Transition in Layered Chalcogenide TaSe$_{2-x}$Te$_{x}$ Lin-Lin Wei, Shuai-Shuai Sun, Kai Sun, Yu Liu, Ding-Fu Shao, Wen-Jian Lu, Yu-Ping Sun, Huan-Fang Tian, Huai-Xin Yang Chin. Phys. Lett. 2017, 34 (8): 086101 .   DOI: 10.1088/0256-307X/34/8/086101 Abstract   PDF(pc) (2332KB) ( 629 ) PDF(mobile)(2317KB) ( 15 ) HTML ( 8 )  The structural features and three-dimensional nature of the charge density wave (CDW) state of the layered chalcogenide 1T-TaSe$_{2-x}$Te$_{x}$ ($0\le x\le 2.0$) are characterized by Cs-corrected transmission electron microscopy measurements. Notable changes of both average structure and the CDW state arising from Te substitution for Se are clearly demonstrated in samples with $x>0.3$. The commensurate CDW state characterized by the known star-of-David clustering in the 1T-TaSe$_{2}$ crystal becomes visibly unstable with Te substitution and vanishes when $x=0.3$. The 1T-TaSe$_{2-x}$Te$_{x}$ ($0.3\le x\le 1.3$) samples generally adopt a remarkable incommensurate CDW state with monoclinic distortion, which could be fundamentally in correlation with the strong $q$-dependent electron–phonon coupling-induced period-lattice-distortion as identified in TaTe$_{2}$. Systematic analysis demonstrates that the occurrence of superconductivity is related to the suppression of the commensurate CDW phase and the presence of discommensuration is an evident structural feature observed in the superconducting samples.
 Select Local Structure Analysis of Lead Zinc Niobate-Barium Titanate Ceramic by X-Ray Absorption Spectroscopy and Density Functional Calculation Kanokwan Kanchiang, Phakkhananan Pakawanit, Rattikorn Yimnirun Chin. Phys. Lett. 2017, 34 (8): 086102 .   DOI: 10.1088/0256-307X/34/8/086102 Abstract   PDF(pc) (676KB) ( 212 ) PDF(mobile)(672KB) ( 1 ) HTML ( 0 )  The local structure of an alternative Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_{3}$-based perovskite ceramic is investigated. The 0.07BaTiO$_{3}$-0.93Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_{3}$ ceramic is synthesized using a combination of Zn$_{3}$Nb$_{2}$O$_{8}$ $B$-site precursor and BaTiO$_{3}$ perovskite phase stabilizer. Then, x-ray absorption spectroscopy and density functional theory are employed to calculate the local structure configuration and formation energy of the prepared samples. Ba$^{2+}$ is found to replace Pb$^{2+}$ in $A$-site with Zn$^{2+}$ occupying $B$-site in Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_{3}$, while in the neighboring structure, Ti$^{4+}$ replaces Nb$^{5+}$ in $B$-site with Pb$^{2+}$ occupying $A$-site. With the substitution of BaTiO$_{3}$ in Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_{3}$, the bond length between Zn$^{2+}$ and Pb$^{2+}$ is longer than that of the typical perovskite phase of Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_{3}$. This indicates the key role of BaTiO$_{3}$ in decreasing the steric hindrance of Pb$^{2+}$ lone pair, and the mutual interactions between Pb$^{2+}$ lone pair and Zn$^{2+}$ and the formation energy is seen to decrease. This finding of the formation energy and local structure configuration relationship can further extend a fundamental understanding of the role of BaTiO$_{3}$ in stabilizing the perovskite phase in PbZn$_{13}$Nb$_{23}$O$_{3}$-based materials, which in turn will lead to an improved preparation technique for desired electrical properties.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
 Select Pressure-Induced Charge-Order Melting and Reentrant Charge Carrier Localization in the Mixed-Valent Pb$_{3}$Rh$_{7}$O$_{15}$ Yan Li, Zhao Sun, Jia-Wei Cai, Jian-Ping Sun, Bo-Sen Wang, Zhi-Ying Zhao, Y. Uwatoko, Jia-Qiang Yan, Jin-Guang Cheng Chin. Phys. Lett. 2017, 34 (8): 087201 .   DOI: 10.1088/0256-307X/34/8/087201 Abstract   PDF(pc) (859KB) ( 205 ) PDF(mobile)(871KB) ( 9 ) HTML ( 54 )  The mixed-valent Pb$_{3}$Rh$_{7}$O$_{15}$ undergoes a Verwey-type transition at $T_{\rm v} \approx 180$ K, below which the development of Rh$^{3+}$/Rh$^{4+}$ charge order induces an abrupt conductor-to-insulator transition in resistivity. Here we investigate the effect of pressure on the Verwey-type transition of Pb$_{3}$Rh$_{7}$O$_{15}$ by measuring its electrical resistivity under hydrostatic pressures up to 8 GPa with a cubic anvil cell apparatus. We find that the application of high pressure can suppress the Verwey-type transition around 3 GPa, above which a metallic state is realized at temperatures below $\sim$70 K, suggesting the melting of charge order by pressure. Interestingly, the low-temperature metallic region shrinks gradually upon further increasing pressure and disappears completely at $P >7$ GPa, which indicates that the charge carriers in Pb$_{3}$Rh$_{7}$O$_{15}$ undergo a reentrant localization under higher pressures. We have constructed a temperature-pressure phase diagram for Pb$_{3}$Rh$_{7}$O$_{15}$ and compared to that of Fe$_{3}$O$_{4}$, showing an archetype Verwey transition.
 Select Quantum Switch and Efficient Spin-Filter in a System Consisting of Multiple Three-Quantum-Dot Rings Ze-Long He, Ji-Yuan Bai, Shu-Jiang Ye, Li Li, Chun-Xia Li Chin. Phys. Lett. 2017, 34 (8): 087301 .   DOI: 10.1088/0256-307X/34/8/087301 Abstract   PDF(pc) (735KB) ( 191 ) PDF(mobile)(727KB) ( 3 ) HTML ( 3 )  Using the non-equilibrium Keldysh Green's function technique, we investigate electron transport properties of a system consisting of multiple three-quantum-dot rings. The conductance as a function of the electron energy is numerically calculated. An antiresonance point emerges in the conductance spectra and evolves into a well-defined insulating band with the increasing number of three-quantum-dot rings. The position of the well-defined insulating band can be modulated by varying the tunneling coupling strength between adjacent three-quantum-dot rings. When an external magnetic flux is introduced, several to 100% spin-polarized windows will occur due to the Zeeman splitting. These results strongly suggest that this device may realize multiple functions including quantum switch and efficient spin filtering.
 Select Molecular Beam Epitaxy Growth of Tetragonal FeS Films on SrTiO$_{3}$(001) Substrates Kun Zhao, Hai-Cheng Lin, Wan-Tong Huang, Xiao-Peng Hu, Xi Chen, Qi-Kun Xue, Shuai-Hua Ji Chin. Phys. Lett. 2017, 34 (8): 087401 .   DOI: 10.1088/0256-307X/34/8/087401 Abstract   PDF(pc) (1512KB) ( 253 ) PDF(mobile)(1500KB) ( 9 ) HTML ( 7 )  We report the successful growth of the tetragonal FeS film with one or two unit-cell (UC) thickness on SrTiO$_{3}$(001) substrates by molecular beam epitaxy. Large lattice constant mismatch with the substrate leads to high density of defects in single-UC FeS, while it has been significantly reduced in the double-UC thick film due to the lattice relaxation. The scanning tunneling spectra on the surface of the FeS thin film reveal the electronic doping effect of single-UC FeS from the substrate. In addition, at the Fermi level, the energy gaps of approximately 1.5 meV are observed in the films of both thicknesses at 4.6 K and below. The absence of coherence peaks of gap spectra may be related to the preformed Cooper-pairs without phase coherence.
 Select Electronic, Elastic and Piezoelectric Properties of Two-Dimensional Group-IV Buckled Monolayers Jing Shi, Yong Gao, Xiao-Li Wang, Si-Ning Yun Chin. Phys. Lett. 2017, 34 (8): 087701 .   DOI: 10.1088/0256-307X/34/8/087701 Abstract   PDF(pc) (791KB) ( 825 ) PDF(mobile)(777KB) ( 6 ) HTML ( 10 )  Electronic, elastic and piezoelectric properties of two-dimensional (2D) group-IV buckled monolayers (GeSi, SnSi and SnGe) are studied by first principle calculations. According to our calculations, SnSi and SnGe are good 2D piezoelectric materials with large piezoelectric coefficients. The values of $d_{11}$ of SnSi and SnGe are 5.04 pm/V and 5.42 pm/V, respectively, which are much larger than 2D MoS$_{2}$ (3.6 pm/V) and are comparable with some frequently used bulk materials (e.g., wurtzite AlN 5.1 pm/V). Charge transfer is calculated by the Löwdin analysis and we find that the piezoelectric coefficients ($d_{11}$ and $d_{31}$) are highly dependent on the polarizabilities of the anions and cations in group-IV monolayers.
 Select Ionoluminescence Spectra of a ZnO Single Crystal Irradiated with 2.5MeV H$^{+}$ Ions Li Zheng, Guang-Fu Wang, Meng-Lin Qiu, Ying-Jie Chu, Mi Xu, Peng Yin Chin. Phys. Lett. 2017, 34 (8): 087801 .   DOI: 10.1088/0256-307X/34/8/087801 Abstract   PDF(pc) (1615KB) ( 256 ) PDF(mobile)(1614KB) ( 7 ) HTML ( 2 )  The ionoluminescence (IL) spectra of a ZnO single crystal irradiated with 2.5 MeV H$^{+}$ ions reveal that its intensity decreases with increasing the ion fluence, which indicates that the concentration of luminescence centers decreases with irradiation. The Gaussian decomposition results of the ZnO IL spectrum with a fluence of 1.77$\times$10$^{11}$ ions/cm$^{2}$ show that the spectrum is a superposition of energy levels centered at 1.75 eV, 2.10 eV, 3.12 eV and 3.20 eV. The four peaks are associated with electronic transitions from CB to V$_{\rm Zn}$, CB to O$_{\rm i}$, Zn$_{\rm i}$ to VB and the decay of self-trapped excitons, respectively. The results of single-exponential fitting demonstrate that different luminescent centers have different radiation resistance, which may explain why the emission decreases more slowly in the NBE band than in the DBE band. The agglomeration of larger point clusters accounts for the decrease in the concentration of luminescence centers and the increase in the concentration of non-luminescence centers, which indicates that the defect clusters induced by ion implantation act as nonradiative recombination centers and suppress light emission. The results of the photoluminescence spectra of a virgin ZnO single crystal and a ZnO single crystal irradiated with a fluence of 3.4$\times$10$^{14}$ ions/cm$^{2}$ show that compared with the virgin ZnO, the emission intensity of irradiated ZnO decreases by nearly two orders of magnitude, which demonstrates that the irradiation effect reduces radiative recombination and enhances nonradiative recombination. The conclusions of photoluminescence are consistent with the IL results.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
 Select Poisoning of MoO$_{3}$ Precursor on Monolayer MoS$_{2}$ Nanosheets Growth by Tellurium-Assisted Chemical Vapor Deposition Zhi-Gang Wang, Fei Pang Chin. Phys. Lett. 2017, 34 (8): 088101 .   DOI: 10.1088/0256-307X/34/8/088101 Abstract   PDF(pc) (1255KB) ( 498 ) PDF(mobile)(1249KB) ( 4 ) HTML ( 5 )  We obtain molybdenum disulfide (MoS$_{2}$) nanosheets (NSs) with edge sizes of 18 μm by direct sulfuration of MoO$_{3}$ powder spread on the SiO$_{2}$/Si substrates. However, the undesirable MoO$_{3}$ nanoparticles (NPs) left on the surface of MoS$_{2}$ NSs poison the MoO$_{3 }$ precursor. Introducing Te vapors to react with MoS$_{2}$ to form low melting point intermediate MoS$_{x}$Te$_{2-x}$, the evaporations of MoO$_{3}$ precursor recover and MoO$_{3}$ NPs disappear. Thus Te vapor is effective to suppress poisoning of the MoO$_{3}$ precursor. Selecting the appropriate amount of Te vapor, we fabricate monolayer MoS$_{2}$ NSs up to 70 μm in edge length. This finding can be significant to understand the role of Te in the Te-assisted chemical vapor deposition growth process of layered chalcogenide materials.
 Select High Refractive Index Ti$_3$O$_5$ Films for Dielectric Metasurfaces Sohail Abdul Jalil, Mahreen Akram, Gwanho Yoon, Ayesha Khalid, Dasol Lee, Niloufar Raeis-Hosseini, Sunae So, Inki Kim, Qazi Salman Ahmed, Junsuk Rho, Muhammad Qasim Mehmood Chin. Phys. Lett. 2017, 34 (8): 088102 .   DOI: 10.1088/0256-307X/34/8/088102 Abstract   PDF(pc) (1298KB) ( 781 ) PDF(mobile)(1293KB) ( 6 ) HTML ( 25 )  Ti$_3$O$_5$ films are deposited with the help of an electron beam evaporator for their applications in metasurfaces. The film of subwavelength (632 nm) thickness is deposited on a silicon substrate and annealed at 400$^{\circ}\!$C. The ellipsometry result shows a high refractive index above 2.5 with the minimum absorption coefficient in the visible region, which is necessary for high efficiency of transparent metasurfaces. Atomic force microscopy analysis is employed to measure the roughness of the as-deposited films. It is seen from micrographs that the deposited films are very smooth with the minimum roughness to prevent scattering and absorption losses for metasurface devices. The absence of grains and cracks can be seen by scanning electron microscope analysis, which is favorable for electron beam lithography. Fourier transform infrared spectroscopy reveals the transmission and reflection obtained from the film deposited on glass substrates. The as-deposited film shows high transmission above 60%, which is in good agreement with metasurfaces.
 Select Total Ionizing Dose Response of Different Length Devices in 0.13μm Partially Depleted Silicon-on-Insulator Technology Meng-Ying Zhang, Zhi-Yuan Hu, Zheng-Xuan Zhang, Shuang Fan, Li-Hua Dai, Xiao-Nian Liu, Lei Song Chin. Phys. Lett. 2017, 34 (8): 088501 .   DOI: 10.1088/0256-307X/34/8/088501 Abstract   PDF(pc) (1194KB) ( 261 ) PDF(mobile)(1196KB) ( 8 ) HTML ( 3 )  An anomalous total dose effect that the long length device is more susceptible to total ionizing dose than the short one is observed with the 0.13 μm partially depleted silicon-on-insulator technology. The measured results and 3D technology computer aided design simulations demonstrate that the devices with different channel lengths may exhibit an enhanced reverse short channel effect after radiation. It is ascribed to that the halo or pocket implants introduced in processes results in non-uniform channel doping profiles along the device length and trapped charges in the shallow trench isolation regions.
 Select Numerical Analysis of Magnetic-Shielding Effectiveness for Magnetic Resonant Wireless Power Transfer System Wei-Guo Lu, Hui-Rong Li, Wei-Ming Chen, Li-Hui Liu Chin. Phys. Lett. 2017, 34 (8): 088801 .   DOI: 10.1088/0256-307X/34/8/088801 Abstract   PDF(pc) (1676KB) ( 928 ) PDF(mobile)(1678KB) ( 4 ) HTML ( 10 )  Magnetic radiation phenomena appear inevitably in the magnetic-resonance wireless power transfer (MR-WPT) system, and regarding this problem the magnetic-shielding scheme is applied to improve the electromagnetic performance in engineering. In this study, the shielding effectiveness of a two-coil MR-WPT system for different material shields is analyzed in theory using Moser's formula and Schelkunoff's formula. On this basis a candidate magnetic-shielding scheme with a double-layer structure is determined, which has better shielding effectiveness and coils coupling coefficient. Finally, some finite element simulation results validate the correctness of the theoretical analysis, and the shielding effectiveness with the double-layer shield in maximum is 30 dB larger than the one with the single-layer case.