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Volume 34 Issue 3
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GENERAL
Improving Accuracy of Estimating Two-Qubit States with Hedged Maximum Likelihood
Qi Yin, Guo-Yong Xiang, Chuan-Feng Li, Guang-Can Guo
Chin. Phys. Lett. 2017, 34 (3): 030301 .   DOI: 10.1088/0256-307X/34/3/030301
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As a widely used reconstruction algorithm in quantum state tomography, maximum likelihood estimation tends to assign a rank-deficient matrix, which decreases estimation accuracy for certain quantum states. Fortunately, hedged maximum likelihood estimation (HMLE) [Phys. Rev. Lett. 105 (2010) 200504] was proposed to avoid this problem. Here we study more details about this proposal in the two-qubit case and further improve its performance. We ameliorate the HMLE method by updating the hedging function based on the purity of the estimated state. Both performances of HMLE and ameliorated HMLE are demonstrated by numerical simulation and experimental implementation on the Werner states of polarization-entangled photons.
Efficient and Secure Authenticated Quantum Dialogue Protocols over Collective-Noise Channels
Min Xiao, Yun-Ru Cao, Xiu-Li Song
Chin. Phys. Lett. 2017, 34 (3): 030302 .   DOI: 10.1088/0256-307X/34/3/030302
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Based on the deterministic secure quantum communication, we present a novel quantum dialogue protocol without information leakage over the collective noise channel. The logical qubits and four-qubit decoherence-free states are introduced for resisting against collective-dephasing noise, collective-rotation noise and all kinds of unitary collective noise, respectively. Compared with the existing similar protocols, the analyses on security and information-theoretical efficiency show that the proposed protocol is more secure and efficient.
$Ab\ Initio$ Calculation of Dielectric Function in Wurtzite GaN Based on Walter's Model
Zi-Wei Zhu, Ji-Yuan Zheng, Lai Wang, Bing Xiong, Chang-Zheng Sun, Zhi-Biao Hao, Yi Luo, Yan-Jun Han, Jian Wang, Hong-Tao Li
Chin. Phys. Lett. 2017, 34 (3): 030303 .   DOI: 10.1088/0256-307X/34/3/030303
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The wavelength-dependent and frequency-dependent dielectric function of wurtzite-GaN is calculated totally from fundamental parameters such as the lattice constant using Walter's ab initio model. The errors occurring in the calculation are carefully reduced by linear interpolation of energy data. The Kramers–Krönig transform of the real part of greater range is obtained by extrapolation of the real part. The calculation is time-consuming but meaningful. The long-wave results are similar to the experimental data of the photon and are useful for related investigation of properties of wide-gap semiconductors such as electron scattering like the Auger recombination and impact ionization.
Destroying Extremal Kerr–Newman-AdS Black Holes with Test Particles
Yu Song, Hao Tang, De-Cheng Zou, Rui-Hong Yue, Cheng-Yi Sun
Chin. Phys. Lett. 2017, 34 (3): 030401 .   DOI: 10.1088/0256-307X/34/3/030401
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Neglecting the self-force, self-energy and radiative effects, we follow the spirit of Wald's gedanken experiment and further discuss whether an extremal Kerr–Newman-AdS (KNA) black hole can turn into a naked singularity when it captures charged and spinning massive particles. It is found that feeding a test particle into an extremal KNA black hole could lead to a violation of cosmic censorship for the black hole.
Mathematical Constraints in Multiscale Subgrid-Scale Modeling of Nonlinear Systems
Le Fang, Ming-Wei Ge
Chin. Phys. Lett. 2017, 34 (3): 030501 .   DOI: 10.1088/0256-307X/34/3/030501
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To shed light on the subgrid-scale (SGS) modeling methodology of nonlinear systems such as the Navier–Stokes turbulence, we define the concepts of assumption and restriction in the modeling procedure, which are shown by generalized derivation of three general mathematical constraints for different combinations of restrictions. These constraints are verified numerically in a one-dimensional nonlinear advection equation. This study is expected to inspire future research on the SGS modeling methodology of nonlinear systems.
ATOMIC AND MOLECULAR PHYSICS
Probing Ultrafast Dissociation Dynamics of Chloroiodomethane in the B Band by Time-Resolved Mass Spectrometry
Yu-Zhu Liu, Jin-You Long, Lin-Hua Xu, Xiang-Yun Zhang, Bing Zhang
Chin. Phys. Lett. 2017, 34 (3): 033301 .   DOI: 10.1088/0256-307X/34/3/033301
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Ultrafast dissociation dynamics of chloroiodomethane (CH$_{2}$ICl) in the B band is studied by femtosecond time-resolved time-of-flight (TOF) mass spectrometry. Time-resolved TOF mass signal of parent ion (CH$_{2}$ICl$^{+})$ and main daughter ion (CH$_{2}$Cl$^{+})$ are obtained. The curve for the transient signal of CH$_{2}$ICl$^{+}$ is simple and can be well fitted by an exponential decay convoluted with a Gaussian function. The decay constant determined to be less than 35 fs reflects the lifetime of the B band. Significant substituent effects on photodissociation dynamics of CH$_{2}$ICl compared with CH$_{3}$I are discussed. The dissociation time from the parent ion CH$_{2}$ICl$^{+}$ to the daughter ion CH$_{2}$Cl$^{+}$ is determined in the experiment. The optimized geometry of the ionic state of CH$_{2}$ICl and the ionization energy are calculated for further analysis of the measurements. In addition, compared with the parent ion, a new decay component with time constant of $\sim $596 fs is observed for CH$_{2}$Cl$^{+}$, and reasonable mechanisms are proposed for the explanation.
FUNDAMENTAL AREAS OF PHENOMENOLOGY(INCLUDING APPLICATIONS)
Negative Refraction Index Manipulated by a Displaced Squeezed Fock State in the Mesoscopic Dissipative Left-Handed Transmission Line
Hong-Wei Guo, Shun-Cai Zhao, Xiao-Jing Wei, Xin Li
Chin. Phys. Lett. 2017, 34 (3): 034201 .   DOI: 10.1088/0256-307X/34/3/034201
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Negative refractive index (NRI) of the mesoscopic dissipative left-handed transmission line (LHTL) is manipulated by the displaced squeezed Fock state and the dissipation presented by the resistance and conductance. Compared with the classical LHTL, some novel characteristics of NRI are shown in the LHTL because of the quantum effect, which will be significant for its miniaturization application in microwave frequency.
Temporally Modulated Phase Retrieval Method for Weak Temporal Phase Measurement of Laser Pulses
Yu-Dong Yao, Zhi Qiao, Xiao-Chao Wang, Wei Fan, Zun-Qi Lin
Chin. Phys. Lett. 2017, 34 (3): 034202 .   DOI: 10.1088/0256-307X/34/3/034202
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We propose a simple iterative algorithm based on a temporally movable phase modulation process to retrieve the weak temporal phase of laser pulses. This unambiguous method can be used to achieve a high accuracy and to simultaneously measure the weak temporal phase and temporal profile of pulses, which are almost transform-limited. A detailed analysis shows that this iterative method has valuable potential applications in the characterization of pulses with weak temporal phase.
Phase-Shifting-Free Interferometric Cryptosystem
Tuo Li, Yi-Shi Shi
Chin. Phys. Lett. 2017, 34 (3): 034203 .   DOI: 10.1088/0256-307X/34/3/034203
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Conventional phase-shifting interferometry-based (PSI-based) cryptosystem needs at least two-step phase-shifting. In this work, we propose a phase-shifting-free interferometric cryptosystem, which needs only one interferogram recording. Since the phase-shifting step is not required in the proposed cryptosystem, not only the low encryption speed which is a bottleneck problem of the conventional PSI-based one is solved, but also the setup of the cryptosystem is simplified. A series of simulation experimental results demonstrate the validity and robustness of the proposed cryptosystem.
Widely Tunable Two-Section Directly Modulated DBR Lasers for TWDM-PON System
Dai-Bing Zhou, Song Liang, Liang-Shun Han, Ling-Juan Zhao, Wei Wang
Chin. Phys. Lett. 2017, 34 (3): 034204 .   DOI: 10.1088/0256-307X/34/3/034204
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Wavelength tunable and directly modulated distributed Bragg reflector (DBR) lasers with butt-joint technology are designed, fabricated and characterized. The DBR laser consists of a gain section and a DBR section. To increase the electrical isolation between the gain section and the DBR section, parts of a p-doped material in the isolation region are etched off selectively. Over 2 k$\Omega$ isolation resistance is realized ultimately without the need of ion implantation, which simplifies the fabrication process. The laser exhibits high speed modulation with a large tunable range. The 3 dB direct modulation bandwidth of the device is over 8 GHz in a 12 nm tunable range. This widely tunable DBR laser with the simple structure is promising as a colorless light source for the next-generation time and wavelength division multiplexed passive optical network (TWDM-PON) systems.
Q-Switching Pulse Operation in 1.5-μm Region Using Copper Nanoparticles as Saturable Absorber
A. R. Muhammad, M. T. Ahmad, R. Zakaria, H. R. A. Rahim, S. F. A. Z. Yusoff, K. S. Hamdan, H. H. M. Yusof, H. Arof, S. W. Harun.
Chin. Phys. Lett. 2017, 34 (3): 034205 .   DOI: 10.1088/0256-307X/34/3/034205
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We demonstrate a passively Q-switched erbium-doped fiber laser (EDFL) using a copper nanoparticle (CuNP) thin film as the saturable absorber in a ring cavity. A stable Q-switched pulse operation is observed as the CuNP saturable absorber (SA) is introduced in the cavity. The pulse repetition rate of the EDFL is observed to be proportional to the pump power, and is limited to 101.2 kHz by the maximum pump power of 113.7 mW. On the other hand, the pulse width reduces from 10.19 μs to 4.28 μs as the pump power is varied from 26.1 mW to 113.7 mW. The findings suggest that CuNP SA could be useful as a potential saturable absorber for the development of the robust, compact, efficient and low cost Q-switched fiber laser operating at 1.5-μm region.
A High-Pulse-Energy High-Beam-Quality Tunable Ti:Sapphire Laser Using a Prism-Dispersion Cavity
Chang Xu, Shi-Bo Dai, Chuan Guo, Qi Bian, Jun-Wei Zuo, Yuan-Qin Xia, Hong-Wei Gao, Zhi-Min Wang, Yong Bo, Nan Zong, Sheng Zhang, Qin-Jun Peng, Zu-Yan Xu
Chin. Phys. Lett. 2017, 34 (3): 034206 .   DOI: 10.1088/0256-307X/34/3/034206
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A high-pulse-energy high-beam-quality tunable Ti:sapphire laser pumped by a frequency-doubled Nd:YAG laser is demonstrated. Using a fused-silica prism as the dispersion element, a tuning range of 740–855 nm is obtained. At an incident pump energy of 774 mJ, the maximum output energy of 104 mJ at 790 nm with a pulse width of 100 μs is achieved at a repetition rate of 5 Hz. To the best of our knowledge, it is the highest pulse energy at 790 nm with pulse width of hundred micro-seconds for an all-solid-state laser. The linewidth of output is 0.5 nm, and the beam quality factor $M^{2}$ is 1.16. The high-pulse-energy high-beam-quality tunable Ti:sapphire laser in the range of 740–855 nm can be used to establish a more accurate and consistent absolute scale of second-order optical-nonlinear coefficients for KBe$_{2}$BO$_{3}$F$_{2}$ measured in a wider wavelength range and to assess Miller's rule quantitatively.
Transmission Spectral Characteristics of Photonic Crystals Milled in Annealed Proton-Exchange LiNbO$_3$ Waveguide
Quan-Zhou Zhao, De-Long Zhang
Chin. Phys. Lett. 2017, 34 (3): 034207 .   DOI: 10.1088/0256-307X/34/3/034207
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Transmission spectra of triangular lattice photonic crystals milled in the top surface of an annealed proton-exchange waveguide are numerically simulated. The effects of the finite depth, conical shape, trapezoidal shape and hybrid shape of holes are theoretically analyzed. Due to the difficulty of milling high aspect-ratio cylindrical holes in lithium niobate (LiNbO$_3$), a compromised solution is proposed to improve the overlap between shallow holes and the waveguide mode, and useful transmission spectra with strong contrast and sharp band edges are achieved.
Cs 5$D_ {5/2}$–$6F$ 728nm Laser Spectroscopy with Single Pumping Laser
Qi Zhou, Peng-Yuan Chang, Zhong-Zheng Liu, Xiao-Gang Zhang, Chuan-Wen Zhu, Jing-Biao Chen
Chin. Phys. Lett. 2017, 34 (3): 034208 .   DOI: 10.1088/0256-307X/34/3/034208
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The sub-Doppler absorption laser spectroscopy at 728 nm transition from the 5$D_ {5/2}$ state to the $6F$ state of cesium with linewidth near 10 MHz is first experimentally performed with indirect pumping from the ground state 6$S_{1/2}$ to the state 7$P_{3/2}$ by a 455.5 nm diode laser. Using a 455.5 nm diode laser as an indirect pump laser, several excited states will be populated due to spontaneous decay from the $7P$ state. We first implement the sub-Doppler absorption laser spectroscopy at 728 nm from the 5$D_ {5/2}$ state to the $6F$ state when Cs atoms within thermal glass cell decay to the 5$D_ {5/2}$ state. Due to velocity transfer effect, the hyperfine structure of 5$D_ {5/2}$ shows a mixed and complicated pattern but very clear structure when the 455.5 nm pumping laser is counter-propagating (or co-propagating) with the 728 nm probing laser.
External Cavity Tuning of Coherent Quantum Cascade Laser Array Emitting at $\sim$7.6μm
Chuan-Wei Liu, Jin-Chuan Zhang, Fang-Liang Yan, Zhi-Wei Jia, Zhi-Bin Zhao, Ning Zhuo, Feng-Qi Liu, Zhan-Guo Wang
Chin. Phys. Lett. 2017, 34 (3): 034209 .   DOI: 10.1088/0256-307X/34/3/034209
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An external cavity quantum cascade laser (QCL) array with a wide tuning range and high output power is presented. The coherent QCL array combined with a diffraction grating and gold mirror is tuned in the Littrow configuration. Taking advantage of the single-lobed fundamental supermode far-field pattern, the tuning capability of 30.6 cm$^{-1}$ is achieved with a fixed injected current of 3.5 A at room temperature. Single-mode emission can be observed in the entire process. The maximum single-mode output power of the external cavity setup is as high as 25 mW and is essential in real applications.
A Highly Compact Third-Order Silicon Elliptical Micro-Ring Add-Drop Filter with a Large Free Spectral Range
Huan Guan, Zhi-Yong Li, Hai-Hua Shen, Rui Wang, Yu-De Yu
Chin. Phys. Lett. 2017, 34 (3): 034210 .   DOI: 10.1088/0256-307X/34/3/034210
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We demonstrate a highly compact third-order elliptical micro-ring add-drop filter based on a silicon-on-insulator wafer. The elliptical micro-ring resonator has a major radius of 6 μm (minor radius of 4.112 μm) and a large free spectral range of 18 nm. Experimental results show a box-like channel dropping response, which has a 3 dB bandwidth of $\sim$2.7 nm, high out-of-band signal rejection of around 40 dB and a very low drop loss ($ < $0.5 dB). Simulation agrees well with the experiments. The footprint of the whole chip is only 0.0003 mm$^{2}$.
Interference from Two-Photon Sources in Silica-on-Silicon Circuits at Telecom Wavelength
Xing-Yun Li, Lu Qin, Jia-Shun Zhang, Mei-Zhen Ren, Jun-Ming An, Xiao-Hong Yang, Xing-Sheng Xu
Chin. Phys. Lett. 2017, 34 (3): 034211 .   DOI: 10.1088/0256-307X/34/3/034211
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The integrated photonic chip is a promising way to realize future quantum technology. Here we demonstrate a two-photon interference in the standard telecommunication band on a silica-on-silicon integrated photonic chip. Two identical photons in the 1.55 μm band, which are indistinguishable in spatial, frequency and polarization, are generated by type-I collinear spontaneous parametric down-conversion via bismuth borate. The silica-on-silicon integrated chip, which has an insertion loss less than 1 dB, is a Mach–Zehnder interferometer with a thermo-optic phase shifter. A high visibility of 100% in the classical interference and 99.2% in the two-photon interference is achieved, indicating that the two-photon interference with high interference visibility on the chip is attained successfully.
Geoacoustic Inversion for Bottom Parameters via Bayesian Theory in Deep Ocean
Xiao-Le Guo, Kun-De Yang, Yuan-Liang Ma
Chin. Phys. Lett. 2017, 34 (3): 034301 .   DOI: 10.1088/0256-307X/34/3/034301
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We develop a new approach to estimating bottom parameters based on the Bayesian theory in deep ocean. The solution in a Bayesian inversion is characterized by its posterior probability density (PPD), which combines prior information about the model with information from an observed data set. Bottom parameters are sensitive to the transmission loss (TL) data in shadow zones of deep ocean. In this study, TLs of different frequencies from the South China Sea in the summer of 2014 are used as the observed data sets. The interpretation of the multidimensional PPD requires the calculation of its moments, such as the mean, covariance, and marginal distributions, which provide parameter estimates and uncertainties. Considering that the sensitivities of shallow-zone TLs vary for different frequencies of the bottom parameters in the deep ocean, this research obtains bottom parameters at varying frequencies. Then, the inversion results are compared with the sampling data and the correlations between bottom parameters are determined. Furthermore, we show the inversion results for multi-frequency combined inversion. The inversion results are verified by the experimental TLs and the numerical results, which are calculated using the inverted bottom parameters for different source depths and receiver depths at the corresponding frequency.
Localization in an Acoustic Cavitation Cloud
Bo-Ya Miao, Yu An
Chin. Phys. Lett. 2017, 34 (3): 034302 .   DOI: 10.1088/0256-307X/34/3/034302
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Using a nonlinear sound wave equation for a bubbly liquid in conjunction with an equation for bubble pulsation, we theoretically predict and experimentally demonstrate the appearance of a gap in the frequency spectrum of a sound wave propagating in a cavitation cloud comprising bubbles. For bubbles with an ambient radius of 100 μm, the calculations reveal that this gap corresponds to the phenomenon of sound wave localization. For bubbles with an ambient radius of 120 μm, this spectral gap is related to a forbidden band of the sound wave. In the experiment, we observe the predicted gap in the frequency spectrum in soda water. However, in tap water, no spectral gap is present because the bubbles are much smaller than 100 μm.
Determination of Slip Length in Couette Flow Based on an Analytical Simulation Incorporating Surface Interaction
Xin Zhao, Chao Wei, Shi-Hua Yuan
Chin. Phys. Lett. 2017, 34 (3): 034701 .   DOI: 10.1088/0256-307X/34/3/034701
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An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account of the micro-force between molecules and macro-force from the viscous shearing effect, as they contribute to the achievement of the slip length. The calculated results are compared with those obtained from the molecular dynamics simulation, showing an excellent agreement. Further, the effect of the shear rate on the slip is investigated. The results can well predict the fluid flow behaviors on a solid substrate, but has to be proved by experiment.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
Ramp-Wave Compression Experiment with Direct Laser Illumination on ShenGuang-III Prototype Laser Facility
Feng Wang, Quan-Xi Xue, Teng Ji, Yu-Long Li, Tao Xu, Xiao-Shi Peng
Chin. Phys. Lett. 2017, 34 (3): 035201 .   DOI: 10.1088/0256-307X/34/3/035201
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Ramp-wave compression experiment to balance the high compression pressure generation in aluminum and x-ray blanking effect in transparent window is demonstrated with an imaging velocity interferometer system for any reflector (VISAR) on ShenGuang-III prototype laser facility. The highest pressure is about 500 GPa after using the multilayer target design Al/Au/Al/LiF and $\sim$10$^{13}$ W/cm$^{2}$ laser pulse illuminated on the planar Al target, which generates the spatial uniformity to $ < $1% over 500 μm on the ablation layer. A 2-μm-thick Au layer is used to prevent the x-ray from preheating the planar ablation Al layer and window material LiF. The imaging VISAR system can be used to record the abrupt loss of the probe beam ($\lambda=532$ nm) caused by absorption and reflection of 20-μm, 30-μm and 40-μm-thick Al, i.e., the blanking effect. Although there are slight shocks in the target, the peak pressure 500 GPa, which is the highest data up to now, is obtained with ramp-wave compression.
On the Time Fractional Modulation for Electron Acoustic Shock Waves
H. G. Abdelwahed, E. K. El-Shewy, A. A. Mahmoud
Chin. Phys. Lett. 2017, 34 (3): 035202 .   DOI: 10.1088/0256-307X/34/3/035202
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Nonlinear features of electron-acoustic shock waves are studied. The Burgers equation is derived and converted to the time fractional Burgers equation by Agrawal's method. Using the Adomian decomposition method, the shock wave solutions of the time fractional Burgers equation are constructed. The effect of time fractional parameter on the shock wave properties in auroral plasma is investigated.
Self-Organization of Charged Particulates in the Presence of External Force
You-Mei Wang, Qi Chen, Ming-Young Yu
Chin. Phys. Lett. 2017, 34 (3): 035203 .   DOI: 10.1088/0256-307X/34/3/035203
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Evolution of spatial distribution of charged particulates under the action of an external force is investigated. It is found that starting from a homogeneous Maxwellian distribution of particulates, clusters can form and aggregate. The evolution process, as well as the asymptotic number and configuration of the clusters formed, depends strongly on the strength of the external force. The particulates in most of the final clusters are in the crystal state, as can also be deduced from the corresponding velocity and auto-correlation functions.
CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES
Microstructural Changes of Graphene/PLA/PBC Nanofibers by Electrospinning during Tensile Tests
Wei-Dong Cheng, Chuan-Hui Ren, Xiao-Hua Gu, Zhao-Jun Wu, Xue-Qing Xing, Guang Mo, Zhong-Jun Chen, Zhong-Hua Wu
Chin. Phys. Lett. 2017, 34 (3): 036101 .   DOI: 10.1088/0256-307X/34/3/036101
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This study focuses on the nanostructure and nanostructural changes of novel graphene/poly(lactic acid) (PLA)/ poly(butylene carbonate) (PBC) nanofibers via electrospinning, which are characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), tensile test and in situ small angle x-ray scattering. DSC indicates that the endothermic peak at 295$^\circ\!$C of pure PLA/PBC nanofibers shifted from 317$^{\circ}\!$C to lower 290$^{\circ}\!$C with the increasing graphene content. SEM observations reveal a fine dispersion of graphene in the nanofiber matrices. The graphene/PLA/PBC nanofibers exhibit good improvements in mechanical property. The tensile strength of nanofibers increases with the addition of 0.01 g graphene but reduces with further addition of 0.04 g graphene. The scattering intensities increase dramatically when the strain levels are higher than the yield point due to the nucleation and growth of nanovoids or crystals. However, the increasing content of graphene in the PLA/PBC matrix provokes a strong restriction to the deformation-induced crystals.
Topological Phonon Modes in a Two-Dimensional Wigner Crystal
Wen-Cheng Ji, Jun-Ren Shi
Chin. Phys. Lett. 2017, 34 (3): 036301 .   DOI: 10.1088/0256-307X/34/3/036301
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We investigate the spin–orbit coupling effect in a two-dimensional (2D) Wigner crystal. It is shown that sufficiently strong spin–orbit coupling and an appropriate sign of $g$-factor could transform the Wigner crystal to a topological phonon system. We demonstrate the existence of chiral phonon edge modes in finite size samples, as well as the robustness of the modes in the topological phase. We explore the possibility of realizing the topological phonon system in 2D Wigner crystals confined in semiconductor quantum wells/heterostructure. It is found that the spin–orbit coupling is too weak for driving a topological phase transition in these systems. It is argued that one may look for topological phonon systems in correlated Wigner crystals with emergent effective spin–orbit coupling.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
Electronic Structure and Thermoelectric Power Factor of Na$_{x}$CoO$_{2}$ from First-Principles Calculation
Peng-Xian Lu, Rui-Xia Zhao
Chin. Phys. Lett. 2017, 34 (3): 037101 .   DOI: 10.1088/0256-307X/34/3/037101
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To investigate the relationship between the electronic structure and the power factor of Na$_{x}$CoO$_{2}$ ($x=0.3$, 0.5 and 1.0), the first-principles calculation is conducted by using density functional theory and the semi-classical Boltzmann theory. Our results suggest that with the decreasing Na content, a transition from semiconductor to semimetal is observed. Na$_{0.3}$CoO$_{2}$ possesses a higher electrical conductivity at 1000 K due to its increased density of states near the Fermi energy level. However, an optimal Seebeck coefficient at 1000 K is obtained in Na$_{0.5}$CoO$_{2}$ because of its broadened band gap near the Fermi energy level. Consequently, a maximum power factor is realized in Na$_{0.5}$CoO$_{2}$. Thus our work provides a complete understanding of the relationship between the electronic structure and the thermoelectric power factor of Na$_{x}$CoO$_{2}$.
Anomalous Magneto-Transport Behavior in Transition Metal Pentatelluride HfTe$_{5}$
Ling-Xiao Zhao, Xiao-Chun Huang, Yu-Jia Long, Dong Chen, Hui Liang, Zhan-Hai Yang, Mian-Qi Xue, Zhi-An Ren, Hong-Ming Weng, Zhong Fang, Xi Dai, Gen-Fu Chen
Chin. Phys. Lett. 2017, 34 (3): 037102 .   DOI: 10.1088/0256-307X/34/3/037102
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There is a long-standing confusion concerning the physical origin of the anomalous resistivity peak in transition metal pentatelluride HfTe$_{5}$. Several mechanisms, such as the formation of charge density wave or polaron, have been proposed, but so far no conclusive evidence has been presented. In this work, we investigate the unusual temperature dependence of magneto-transport properties in HfTe$_{5}$. It is found that a three-dimensional topological Dirac semimetal state emerges only at around $T_{\rm p}$ (at which the resistivity shows a pronounced peak), as manifested by a large negative magnetoresistance. This accidental Dirac semimetal state mediates the topological quantum phase transition between the two distinct weak and strong topological insulator phases in HfTe$_{5}$. Our work not only provides the first evidence of a temperature-induced critical topological phase transition in HfTe$_{5}$ but also gives a reasonable explanation on the long-lasting question.
Observation of an Even–Odd Asymmetric Transport in High Landau Levels
Guang-Tong Liu, Yu-Ying Zhu, Qin Wang, Yuan Pang, Jie Fan, Xiu-Nian Jing, Zhong-Qing Ji, Chang-Li Yang, Li Lu, Rui-Rui Du, L. N. Pfeiffer, K. W. West
Chin. Phys. Lett. 2017, 34 (3): 037301 .   DOI: 10.1088/0256-307X/34/3/037301
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Magnetotransport experiments including tilt fields are performed on ultrahigh mobility L-shaped Hall-bar samples of GaAs/AlGaAs quantum wells. The low-temperature longitudinal resistivity ($\rho_{xx}$) data demonstrate that a striking even–odd asymmetric transport exists along the [1$\overline{1}$0] direction at half filling in $N\geq 2$ high Landau levels. Although the origin for the peculiar even–odd asymmetry remains unclear, we propose that the coupling strength between electrons within the same Landau level and between the neighboring two Landau levels should be considered in future studies. The tilt field data show that the in-plane field can suppress the formation of both bubble and stripe phases.
CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Significant Improvement of Passivation Performance by Two-Step Preparation of Amorphous Silicon Passivation Layers in Silicon Heterojunction Solar Cells
Yue Zhang, Cao Yu, Miao Yang, Lin-Rui Zhang, Yong-Cai He, Jin-Yan Zhang, Xi-Xiang Xu, Yong-Zhe Zhang, Xue-Mei Song, Hui Yan
Chin. Phys. Lett. 2017, 34 (3): 038101 .   DOI: 10.1088/0256-307X/34/3/038101
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The key feature of amorphous/crystalline silicon heterojunction solar cells is extremely low surface recombination, which is related to superior passivation on the crystalline silicon wafer surface using thin hydrogenated amorphous silicon (a-Si:H) layers, leading to a high open-circuit voltage. In this work, a two-step method of a-Si:H passivation is introduced, showing excellent interface passivation quality, and the highest effective minority carrier lifetime exceeds 4500 μs. By applying a buffer layer deposited through pure silane plasma, the risk of film epitaxial growth and plasma damage caused by hydrogen diluted silane plasma is effectively reduced. Based on this, excellent passivation is realized through the following hydrogen diluted silane plasma process with the application of high density hydrogen. In this process, hydrogen diffuses to a-Si/c-Si interface, saturating residual dangling bonds which are not passivated by the buffer layer. Employing this two-step method, a heterojunction solar cell with an area of 239 cm$^{2}$ is prepared, yielding to open-circuit voltage up to 735 mV and total-area efficiency up to 22.4%.
Theoretical Modeling of Luminous Efficacy for High-Power White Light-Emitting Diodes
Xue-Hui Tao, Yong Yang
Chin. Phys. Lett. 2017, 34 (3): 038501 .   DOI: 10.1088/0256-307X/34/3/038501
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The photometric characteristics of high-power white light-emitting diode (LED) devices are investigated. A theoretical model for the luminous efficacy of high-power white LED devices and LED systems is proposed. With the proposed theoretical model, the mechanism of the luminous efficacy decrease is explained. Meanwhile, the model can be used to estimate the luminous efficacy of LEDs under general operation conditions, such as different operation temperatures and injection currents. The wide validity of the luminous efficacy model is experimentally verified through the measurements of different types of LEDs. The experimental results demonstrate a high estimation accuracy. The proposed models not only can be applied to estimate the LED photometric performance, but also is helpful for reliability research of LEDs.
Memristive Behavior Based on Ba-Doped SrTiO$_{3}$ Films
Gang Dou, Yang Yu, Mei Guo, Yu-Man Zhang, Zhao Sun, Yu-Xia Li
Chin. Phys. Lett. 2017, 34 (3): 038502 .   DOI: 10.1088/0256-307X/34/3/038502
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The Sr$_{0.95}$Ba$_{0.05}$TiO$_{3}$ (SBT) nanometer film is prepared on the commercially available Pt/TiO$_{2}$/SiO$_{2}$/Si substrate by radio-frequency magnetron sputtering. The x-ray diffraction pattern and the scanning electron microscope image of the cross-sectional profile of the SBT nanometer film are depicted. The memristive mechanism is inferred. The mathematical model $M(q)=12.3656-267.4038|q(t)|$ is calculated, where $M(q)$ denotes the memristance depending on the quantity of electric charge, and $q(t)$ denotes the quantity of electric charge depending on the time. The theoretical $I$–$V$ characteristics of the SBT nanometer film are obtained by the mathematical model. The results show that the theoretical $I$–$V$ characteristics are consistent with the measured $I$–$V$ characteristics. Moreover, the mathematical model could guide the research on applications of the memristor.
31 articles