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 Select Rejuvenation in Hot-Drawn Micrometer Metallic Glassy Wires Jie Dong, Yi-Hui Feng, Yong Huan, Jun Yi, Wei-Hua Wang, Hai-Yang Bai, Bao-An Sun Chin. Phys. Lett.    2020, 37 (1): 017103 .   DOI: 10.1088/0256-307X/37/1/017103 Abstract   HTML   PDF (1089KB) We report an enhanced rejuvenation in hot-drawn micrometer metallic glassy wires (MG wires) with the size reduction. Compared to metallic glasses (MGs) in bulk form, the modulus and hardness for the micro-scale MG wires, tested by nanoindentation methods, are much lower and decrease with the decreasing size, with a maximum decrease of $\sim$26% in modulus and $\sim$17% in hardness. This pronounced rejuvenation is evidenced by the larger sub-$T_{\rm g}$ relaxation enthalpy of the MG wires. The pronounced rejuvenation is physically related to the higher energy state induced by a combined effect of severely thermomechanical shearing and freezing the shear flow into a constrained small-volume region. Our results reveal that the internal states and properties of MGs can be dramatically changed by a proper modulation of temperature, flow stress and size.
 Select Coherent Transfer of Excitation in a Nanomechanical Artificial Lattice Liang Zhang, Tian Tian, Pu Huang, Shaochun Lin, Jiangfeng Du Chin. Phys. Lett.    2020, 37 (1): 014501 .   DOI: 10.1088/0256-307X/37/1/014501 Abstract   HTML   PDF (1822KB) We realize a coherent transfer of mechanical excitation in a finely controlled artificial nanomechanical lattice. We also realize strong dynamic coupling between adjacent high-$Q$ mechanical resonators, via modulated dielectric force at the frequency difference between them. An excitation transfer across a lattice consisting of 7 nanobeams is observed by applying a design sequence of switching for couplings, with the final effective population reaching 0.94. This work not only demonstrates the ability to fully control an artificial lattice but also provides an efficient platform for studying complicated dynamics in one-dimensional systems.
 Select Observation of Shubnikov-de Haas Oscillations in Large-Scale Weyl Semimetal WTe$_{2}$ Films Yequan Chen, Yongda Chen, Jiai Ning, Liming Chen, Wenzhuo Zhuang, Liang He, Rong Zhang, Yongbing Xu, Xuefeng Wang Chin. Phys. Lett.    2020, 37 (1): 017104 .   DOI: 10.1088/0256-307X/37/1/017104 Abstract   HTML   PDF (1303KB) Topological Weyl semimetal WTe$_{2}$ with large-scale film form has a promising prospect for new-generation spintronic devices. However, it remains a hard task to suppress the defect states in large-scale WTe$_{2}$ films due to the chemical nature. Here we significantly improve the crystalline quality and remove the Te vacancies in WTe$_{2}$ films by post annealing. We observe the distinct Shubnikov-de Haas quantum oscillations in WTe$_{2}$ films. The nontrivial Berry phase can be revealed by Landau fan diagram analysis. The Hall mobility of WTe$_{2}$ films can reach 1245 cm$^{2}$V$^{-1}$s$^{-1}$ and 1423 cm$^{2}$V$^{-1}$s$^{-1}$ for holes and electrons with the carrier density of $5\times 10^{19}$ cm$^{-3}$ and $2\times 10^{19}$ cm$^{-3}$, respectively. Our work provides a feasible route to obtain high-quality Weyl semimetal films for the future topological quantum device applications.
 Select Critical Scaling Behaviors of Entanglement Spectra Qi-Cheng Tang, Wei Zhu Chin. Phys. Lett.    2020, 37 (1): 010301 .   DOI: 10.1088/0256-307X/37/1/010301 Abstract   HTML   PDF (1294KB) We investigate the evolution of entanglement spectra under a global quantum quench from a short-range correlated state to the quantum critical point. Motivated by the conformal mapping, we find that the dynamical entanglement spectra demonstrate distinct finite-size scaling behaviors from the static case. As a prototypical example, we compute real-time dynamics of the entanglement spectra of a one-dimensional transverse-field Ising chain. Numerical simulation confirms that the entanglement spectra scale with the subsystem size $l$ as $\sim$$l^{-1}$ for the dynamical equilibrium state, much faster than $\propto$ $\ln^{-1} l$ for the critical ground state. In particular, as a byproduct, the entanglement spectra at the long time limit faithfully gives universal tower structure of underlying Ising criticality, which shows the emergence of operator-state correspondence in the quantum dynamics.
 Select Repeater-Assisted Zeno Effect in Classical Stochastic Processes GU Shi-Jian**, WANG Li-Gang, WANG Zhi-Guo, LIN Hai-Qing Chin. Phys. Lett.    2012, 29 (1): 010303 .   DOI: 10.1088/0256-307X/29/1/010303 Abstract   PDF (1002KB) We address the possibility of the classical Zeno effect in classical stochastic processes as sampled by transferring a digitized image through a classical channel with surrounding noise. It is shown that the the classical state of the image decays inevitably with the distance of the channel due to the interference of the surroundings. However, if there are enough repeaters, which can both check and recover the state's information, the classical state's decay rate will be significantly suppressed, then a classical Zeno effect might occur.
 Select Partially Overlapped Dual Laser Beams to Reduce Ablation Craters Meng-Han Wang, Jun-Le Qu, Ming Zhu Chin. Phys. Lett.    2020, 37 (1): 015202 .   DOI: 10.1088/0256-307X/37/1/015202 Abstract   HTML   PDF (2790KB) We present our experimental ablation results for partially overlapped dual nanosecond laser beams (PO-DB) on metal and glass surfaces. Numerical simulations are performed to evaluate the crater reduction potential of the PO-DB setup. Damage probability experiments proved the collaboration of two beams within the overlap region. Bright-field and three-dimensional profile measurements verify the reduced ablation area from the proposed PO-DB scheme. Laser-induced plasma is generated when transparent glass is ablated. Atomic emission of Na I ($\sim$589.95 nm) shows comparable signal between the PO-DB set and the traditional single laser beam set. The proposed PO-DB ablation mechanism could also be applied to femtosecond laser systems.
 Select Predicting Quantum Many-Body Dynamics with Transferable Neural Networks Ze-Wang Zhang, Shuo Yang, Yi-Hang Wu, Chen-Xi Liu, Yi-Min Han, Ching-Hua Lee, Zheng Sun, Guang-Jie Li, Xiao Zhang Chin. Phys. Lett.    2020, 37 (1): 018401 .   DOI: 10.1088/0256-307X/37/1/018401 Abstract   HTML   PDF (1062KB) Advanced machine learning (ML) approaches such as transfer learning have seldom been applied to approximate quantum many-body systems. Here we demonstrate that a simple recurrent unit (SRU) based efficient and transferable sequence learning framework is capable of learning and accurately predicting the time evolution of the one-dimensional (1D) Ising model with simultaneous transverse and parallel magnetic fields, as quantitatively corroborated by relative entropy measurements between the predicted and exact state distributions. At a cost of constant computational complexity, a larger many-body state evolution is predicted in an autoregressive way from just one initial state, without any guidance or knowledge of any Hamiltonian. Our work paves the way for future applications of advanced ML methods in quantum many-body dynamics with knowledge only from a smaller system.
 Select X-Ray Diffraction Pattern of Graphite Oxide MU Shi-Jia, SU Yu-Chang, XIAO Li-Hua, LIU Si-Dong, HU Te, TANG Hong-Bo Chin. Phys. Lett.    2013, 30 (9): 096101 .   DOI: 10.1088/0256-307X/30/9/096101 Abstract   PDF (633KB) X-ray diffraction patterns of graphite oxide (GO) are theoretically simulated as a function of the displacements of carbon atoms using the Debye–Waller factor in terms of the Warren–Bodenstein equation. The results demonstrate that GO has the turbostratically stacked structure. The high order (00l) peaks gradually disappear with the increase in atomic thermal vibrations along c-axis while the (hk0) ones weaken for the vibrations along a-axis. When the displacement deviation ua=0.015 nm and uc=0.100 nm the computed result is consistent with the experimental measurements.
 Select Diagnosis of Methane Plasma Generated in an Atmospheric Pressure DBD Micro-Jet by Optical Emission Spectroscopy ZHANG Jun-Feng, BIAN Xin-Chao, CHEN Qiang, LIU Fu-Ping, LIU Zhong-Wei Chin. Phys. Lett.    2009, 26 (3): 035203 .   DOI: 10.1088/0256-307X/26/3/035203 Abstract   PDF (467KB) Diagnosis of methane plasma, generated in an atmospheric pressure dielectric barrier discharge (DBD) micro-plasma jet with a quartz tube as dielectric material by a 25kHz sinusoidal ac power source, is conducted by optical emission spectroscopy (OES). The reactive radicals in methane plasma such as CH, C2, and Hα are detected in-situ by OES. The possible dissociation mechanism of methane in diluted Ar plasma is deduced from spectra. In addition, the density of CH radical, which is considered as one of the precursors in diamond-like (DLC) film formation, affected by the parameters of input voltage and the feed gas flow rate, is emphasized. With the Boltzmann plots, four Ar atomic spectral lines (located at 675.28nm, 687.13nm, 738.40nm and 794.82nm, respectively) are chosen to calculate the electron temperature, and the dependence of electron temperature on dischargeparameters is also investigated.
 Select Experimental Realization of an Intrinsic Magnetic Topological Insulator Yan Gong, Jingwen Guo, Jiaheng Li, Kejing Zhu, Menghan Liao, Xiaozhi Liu, Qinghua Zhang, Lin Gu, Lin Tang, Xiao Feng, Ding Zhang, Wei Li, Canli Song, Lili Wang, Pu Yu, Xi Chen, Yayu Wang, Hong Yao, Wenhui Duan, Yong Xu, Shou-Cheng Zhang, Xucun Ma, Qi-Kun Xue, Ke He Chin. Phys. Lett.    2019, 36 (7): 076801 .   DOI: 10.1088/0256-307X/36/7/076801 Abstract   HTML   PDF (7918KB) An intrinsic magnetic topological insulator (TI) is a stoichiometric magnetic compound possessing both inherent magnetic order and topological electronic states. Such a material can provide a shortcut to various novel topological quantum effects but remained elusive experimentally for a long time. Here we report the experimental realization of thin films of an intrinsic magnetic TI, MnBi$_{2}$Te$_{4}$, by alternate growth of a Bi$_{2}$Te$_{3}$ quintuple layer and a MnTe bilayer with molecular beam epitaxy. The material shows the archetypical Dirac surface states in angle-resolved photoemission spectroscopy and is demonstrated to be an antiferromagnetic topological insulator with ferromagnetic surfaces by magnetic and transport measurements as well as first-principles calculations. The unique magnetic and topological electronic structures and their interplays enable the material to embody rich quantum phases such as quantum anomalous Hall insulators and axion insulators at higher temperature and in a well-controlled way.
 Select Dependence of Elliptic Flow on Transverse Momentum in √sNN=200 GeV Au-Au and √sNN=2.76 TeV Pb-Pb Collisions LI Bao-Chun, FU Yuan-Yuan, WANG Li-Li, WANG Er-Qin, WEN Xin-Jian, LIU Fu-Hu Chin. Phys. Lett.    2012, 29 (7): 072501 .   DOI: 10.1088/0256-307X/29/7/072501 Abstract   PDF (654KB) We investigate the dependence of elliptic flows v2 on transverse momentum PT for charged hadrons produced in nucleus-nucleus collisions at high energy by using a multi-source thermal model, where the contribution of source interactions is considered. Our calculated results are approximately in agreement with the experimental data over a wider PT range from the PHENIX and ALICE collaborations. It is found that the expansion factor increases linearly with the impact parameter from most central (0–5%) to mid-peripheral (35–40%) collisions.
 Select Observation of Coulomb Gap and Enhanced Superconducting Gap in Nano-Sized Pb Islands Grown on SrTiO$_{3}$ Yonghao Yuan, Xintong Wang, Canli Song, Lili Wang, Ke He, Xucun Ma, Hong Yao, Wei Li, Qi-Kun Xue Chin. Phys. Lett.    2020, 37 (1): 017402 .   DOI: 10.1088/0256-307X/37/1/017402 Abstract   HTML   PDF (1746KB) We report high-resolution scanning tunneling microscopy (STM) study of nano-sized Pb islands grown on SrTiO$_{3}$, where three distinct types of gaps with different energy scales are revealed. At low temperature, we find that the superconducting gap (${\it\Delta}_{\rm s}$) in nano-sized Pb islands is significantly enhanced from the one in bulk Pb, while there is no essential change in superconducting transition temperature $T_{\rm c}$, giving rise to a larger BCS ratio 2${\it\Delta}_{\rm s}/k_{_{\rm B}}T_{\rm c} \sim 8.31$ and implying stronger electron-phonon coupling. The stronger coupling can originate from the interface electron-phonon interactions between Pb islands and SrTiO$_{3}$. As the superconducting gap is totally suppressed under applied magnetic field, the Coulomb gap with apparent V-shape emerges. Moreover, the size of Coulomb gap (${\it\Delta}_{\rm C}$) depends on the lateral size of Pb islands ($R$) with ${\it\Delta}_{\rm C}\sim 1/R^{0.35}$, indicating that quantum size effect can significantly influence electronic correlations. Our experimental results shall shed important light on the interplay among superconductivity, quantum size effect and correlations in nano-sized strong-coupling superconductors.
 Select The Spectral Broadening of Motional Stark Effect in the HL-2A Tokamak JIANG Nan, YU De-Liang, YAN Long-Wen, CAO Jian-Yong, ZHONG Wu-Lu, CHEN Cheng-Yuan, LIU Yi, LEI Guang-Jiu, YANG Qing-Wei, DUAN Xu-Ru Chin. Phys. Lett.    2013, 30 (6): 065201 .   DOI: 10.1088/0256-307X/30/6/065201 Abstract   PDF (667KB) The spectral broadening of motional Stark effect (MSE) is simulated in the HL-2A tokamak, which is in good agreement with the experimental observation. The divergence angle of the neutral beam, finite lens size and beam energy dissociation are the main broadening factors, while the lens size is the most important one. The experimental spectra fitted by multiple Gaussian distributions reveal that the Stark splitting and its full width at half maximum (FWHM) are ～0.07 nm and ～0.19 nm, respectively. Therefore, the π and σ components of the MSE will overlap since the Stark splitting is much smaller than its spectral broadening. A narrowband filter with the FWHM of about 0.16 nm is good enough to isolate the two components for providing the polarization fraction over 50%, which guarantees reasonable measurement precision for magnetic field pitch angle.
 Select Propagation of Fast Magnetoacoustic Waves in Stratified Solar Atmosphere ZHENG Hui-Nan, ZHANG Yuan-Yuan, WANG Shui, WANG Chuan-Bing, LI Yi Chin. Phys. Lett.    2006, 23 (2): 399-402 .   Abstract   PDF (264KB) The characteristics of magnetohydrodynamic fast wave propagation in the solar stratified atmosphere are studied by the ray tracing method. The propagation behaviour of the wavefronts is described in detail. A magnetic field incorporating the characteristics field spreading expected in flux tubes is used, which represents the main feature of an active region. Partly ionization is considered beside the stratified solar atmosphere consisting chromosphere, transition region and corona. The study may explain the characteristics in observations of Moreton and extra-ultraviolet image telescope (EIT) waves. The wavefront incurred by the disturbance initialized at the base of the transition region propagates fast initially due to strong magnetic field, and it slows down when arriving beyond the region of flux-tube. Meanwhile, the wave propagates in the corona with a more consistent speed, as seen in the observation of EIT waves. The speeds and propagated characteristics in chromosphere and corona of the wavefronts are in agreement with those observed in Hα Moreton and EIT waves, respectively.
 Select New View of Ping-Pong Protocol Security Piotr Zawadzki** Chin. Phys. Lett.    2012, 29 (1): 010301 .   DOI: 10.1088/0256-307X/29/1/010301 Abstract   PDF (376KB) The ping-pong protocol offers confidential transmission of classic information without a prior key agreement. It is believed that it is quasi secure in lossless quantum channels. Serious doubts related to the analysis paradigm which has been used so far are presented in the study. The security of the protocol is reconsidered.
 Select Numerical Approximations to the Solution of Ray Tracing through the Crystalline Lens A. Yildirim, A. Gökdoğan, M. Merdan, V. Lakshminarayanan Chin. Phys. Lett.    2012, 29 (7): 074202 .   DOI: 10.1088/0256-307X/29/7/074202 Abstract   PDF (439KB) An approximate analytical solution in the form of a rapidly convergent series for tracing light rays through an inhomogeneous graded index medium is developed, using the multi-step differential transform method based on the classical differential transformation method. Numerical results are compared to those obtained by the fourth-order Runge–Kutta method to illustrate the precision and effectiveness of the proposed method. Results are given in explicit and graphical forms.
 Select Ferromagnetism in Layered Metallic Fe$_{1/4}$TaS$_{2}$ in the Presence of Conventional and Dirac Carriers Jin-Hua Wang, Ya-Min Quan, Da-Yong Liu, Liang-Jian Zou Chin. Phys. Lett.    2020, 37 (1): 017101 .   DOI: 10.1088/0256-307X/37/1/017101 Abstract   HTML   PDF (1393KB) We present the microscopic origin of the ferromagnetism of Fe$_{0.25}$TaS$_{2}$ and its finite-temperature magnetic properties. The band structures of Fe$_{0.25}$TaS$_{2}$ are first obtained by the first-principles calculations and it is found that both conventional and Dirac carriers coexist in metallic Fe$_{0.25}$TaS$_{2}$. Accordingly, considering the spin-orbit coupling of Fe $3d$ ion, we derive an effective Ruderman–Kittle–Kasuya–Yosida-type Hamiltonian between Fe spins in the presence of both the conventional parabolic-dispersion and the Dirac linear-dispersion carriers, which contains a Heisenberg-like, an Ising-like and an XY-like term. In addition, we obtain the ferromagnetic Curie temperature $T_{\rm c}$ by using the cluster self-consistent field method. Our results could address not only the high ferromagnetic Curie temperature but also the large magnetic anisotropy in Fe$_{x}$TaS$_{2}$.
 Select Bipolar Thermoelectrical Transport of SnSe Nanoplate in Low Temperature Li-Yan Zhou, Qi Zheng, Li-Hong Bao, Wen-Jie Liang Chin. Phys. Lett.    2020, 37 (1): 017301 .   DOI: 10.1088/0256-307X/37/1/017301 Abstract   HTML   PDF (750KB) Bulk SnSe is an excellent thermoelectrical material with the highest figure-of-merit value of ZT = 2.8, making it promising in applications. Temperature-dependent electrical and thermoelectrical properties of SnSe nanoplates are studied at low temperature. Conductivity drops and rises again as temperature is lowered. The Seebeck coefficient is positive at room temperature and becomes negative at low temperature. The change of the sign of the Seebeck coefficient indicates influence of bipolar transport of the semiconductive SnSe nanoplate. The bipolar transport is caused by the Fermi energy changing with temperature due to different contributions from donors and acceptors at different temperatures.
 Select Machine Learning to Instruct Single Crystal Growth by Flux Method Tang-Shi Yao, Cen-Yao Tang, Meng Yang, Ke-Jia Zhu, Da-Yu Yan, Chang-Jiang Yi, Zi-Li Feng, He-Chang Lei, Cheng-He Li, Le Wang, Lei Wang, You-Guo Shi, Yu-Jie Sun, Hong Ding Chin. Phys. Lett.    2019, 36 (6): 068101 .   DOI: 10.1088/0256-307X/36/6/068101 Abstract   HTML   PDF (691KB) Growth of high-quality single crystals is of great significance for research of condensed matter physics. The exploration of suitable growing conditions for single crystals is expensive and time-consuming, especially for ternary compounds because of the lack of ternary phase diagram. Here we use machine learning (ML) trained on our experimental data to predict and instruct the growth. Four kinds of ML methods, including support vector machine (SVM), decision tree, random forest and gradient boosting decision tree, are adopted. The SVM method is relatively stable and works well, with an accuracy of 81% in predicting experimental results. By comparison, the accuracy of laboratory reaches 36%. The decision tree model is also used to reveal which features will take critical roles in growing processes.
 Select Reduction of the Far-Field Divergence Angle of an 850nm Multi-Leaf Holey Vertical Cavity Surface Emitting Laser ZHOU Kang**, XU Chen, XIE Yi-Yang, ZHAO Zhen-Bo, LIU Fa, SHEN Guang-Di Chin. Phys. Lett.    2011, 28 (8): 084209 .   DOI: 10.1088/0256-307X/28/8/084209 Abstract   PDF (1603KB) By introducing multi-leaf sectorial holes into an oxidation confined 850 nm vertical cavity surface emitting laser (VCSEL), the far-field divergence angle is reduced. The finite-difference time-domain method is used to simulate the far-field pattern of the multi-leaf holey VCSEL with different etching depths and different shapes of the oxide aperture in diameter R. Based on the simulation result, we design and fabricate a multi−leaf holey VCSEL and its divergence angle is only 6°. The experimental results agree well with the theoretical predication.
 Select A High-Sensitivity Terahertz Detector Based on a Low-Barrier Schottky Diode Xiao-Yu Liu, Yong Zhang, De-Jiao Xia, Tian-Hao Ren, Jing-Tao Zhou, Dong Guo, Zhi Jin Chin. Phys. Lett.    2017, 34 (7): 070701 .   DOI: 10.1088/0256-307X/34/7/070701 Abstract   HTML   PDF (1269KB) A low-barrier Schottky barrier diode based on the InGaAs/InP material system is designed and fabricated with a new non-destructive dry over-etching process. By using this diode, a high-sensitivity waveguide detector is proposed. The measured maximum responsivity is over 2000 mV/mW at 630 GHz. The measured noise effective power (NEP) is less than 35 pW/Hz$^{0.5}$ at 570–630 GHz. The minimum NEP is 14 pW/Hz$^{0.5}$ at 630 GHz. The proposed high-sensitivity waveguide detector has the characteristics of simple structure, compact size, low cost and high performance, and can be used in a variety of applications such as imaging, molecular spectroscopy and atmospheric remote sensing.
 Select Resistivity and Radio-Frequency Properties of Two-Generation Trap-Rich Silicon-on-Insulator Substrates Lei Zhu, Yong-Wei Chang, Nan Gao, Xin Su, YeMin Dong, Lu Fei, Xing Wei, Xi Wang Chin. Phys. Lett.    2018, 35 (4): 047302 .   DOI: 10.1088/0256-307X/35/4/047302 Abstract   HTML   PDF (1369KB) Crystal morphologies and resistivity of polysilicon trap-rich layers of two-generation trap-rich silicon-on-insulator (TR-SOI) substrates are studied. It is found that the resistivity of the trap-rich layer of generation 2 (TR-G2) is higher than that of generation 1 (TR-G1), although the crystal morphologies of the trap rich layers are the same. In addition, the rf performance of two-generation TR-SOI substrates is investigated by coplanar waveguide lines and inductors. The results show that both the rf loss and the second harmonic distortion of TR-G2 are smaller than those of TR-G1. These results can be attributed to the higher resistivity values of both the trap-rich layer and the high-resistivity silicon (HR-Si) substrate of TR-G2. Moreover, the rf performance of the TR-SOI substrate with thicker buried oxide is slightly better. The second harmonics of various TR-SOI substrates are simulated and evaluated with the harmonic quality factor model as well. It can be predicted that the TR-SOI substrate will see further improvement in rf performance if the resistivities of both the trap-rich layer and HR-Si substrate increase.
 Select Characterization and Magnetic Properties of Nickel Ferrite Nanoparticles Prepared by Ball Milling Technique G. Nabiyouni**, M. Jafari Fesharaki, M. Mozafari, J. Amighian Chin. Phys. Lett.    2010, 27 (12): 126401 .   DOI: 10.1088/0256-307X/27/12/126401 Abstract   PDF (676KB) Nickel ferrite nanoparicles with various grain sizes are synthesized using annealing treatment followed by ball milling of its bulk component materials. Commercially available nickel and iron oxide powders are first mixed, and then annealed at 1100°C in an oxygen environment furnace and for 3 h. The samples are then milled for different times in an SPEX mill. X-ray diffraction pattern indicates that in this stage the sample is single phase. The average grain size is estimated by scanning electron microscopy (SEM) and x-ray diffraction techniques. Magnetic behavior of the sample at room temperature is studied using a superconducting quantum interference device (SQUID). The Curie temperature of the powders is measured by an LCR–meter unit. The x-ray diffraction patterns clearly indicate that increasing the milling time leads to a decrease in the grain size and consequently leads to a decrease in the saturation magnetization as well as the Curie temperatures. This result is attributed to the spin-glass-like surface layer on the nanocrystalline nickel ferrite with a ferrimagnetically aligned core.
 Select Wet Chemical Etching of Antimonide-Based Infrared Materials HAO Hong-Yue, XIANG Wei, WANG Guo-Wei, XU Ying-Qiang, REN Zheng-Wei, HAN Xi, HE Zhen-Hong, LIAO Yong-Ping, WEI Si-Hang, NIU Zhi-Chuan Chin. Phys. Lett.    2015, 32 (10): 107302 .   DOI: 10.1088/0256-307X/32/10/107302 Abstract   PDF (644KB) The roughness and the crystallographic orientation selectivity of etched antimonide-based infrared materials are examined and are used to optimize the chemical mesa etching process of the InAs/GaSb superlattice photodiode with the goal of reducing the dark current. The etchant used is based on phosphoric acid (H3PO4), citric acid (C6H8O7) and hydrogen peroxide (H2O2). The roughness of the mesa sidewalls and etching rates are compared and used to find an optimized etchant, with which we obtain optimized mid-wavelength infrared photodiodes possessing an R0A value of 466 Ω?cm2 and a detectivity of 1.43×1011 cm?Hz1/2W?1. Crystallographic orientation selectivity is seen in InAs etching, and also is seen in the InAs/GaSb superlattice wet chemical etching process.
 Select Physical Properties of [$A_{6}$Cl][Fe$_{24}$Se$_{26}$]($A$=K, Rb) with Self-Similar Structure Shaohua Wang, Qiangwei Yin, Hechang Lei Chin. Phys. Lett.    2020, 37 (1): 017401 .   DOI: 10.1088/0256-307X/37/1/017401 Abstract   HTML   PDF (1481KB) We have successfully synthesized two novel compounds [$A_{6}$Cl][Fe$_{24}$Se$_{26}$] ($A$ = K, Rb). The key structural units of them are FeSe octamers, consisting of edge-shared FeSe$_{4}$ tetrahedra. Two kinds of FeSe octamer layers with different connection configurations stack along the $c$ axis, forming a three-dimensional (3D) TiAl$_{3}$-type structure. Interestingly, the 3D structural topology of these ocatmers in one unit cell is similar to the local atomic arrangement of themselves, i.e., self-similarity in structure. Physical property characterizations indicate that both the compounds exhibit insulating antiferromagnetism with Neel temperatures $T_{\rm N}\sim 110$ K and 75 K for [K$_{6}$Cl][Fe$_{24}$Se$_{26}$] and [Rb$_{6}$Cl][Fe$_{24}$Se$_{26}$].
 Select Investigation of Oxygen Vacancy and Interstitial Oxygen Defects in ZnO Films by Photoluminescence and X-Ray Photoelectron Spectroscopy FAN Hai-Bo, YANG Shao-Yan, ZHANG Pan-Feng, WEI Hong-Yuan, LIU Xiang-Lin, JIAO Chun-Mei, ZHU Qin-Sheng, CHEN Yong-Hai, WANG Zhan-Guo Chin. Phys. Lett.    2007, 24 (7): 2108-2111 .   Abstract   PDF (341KB) ZnO films prepared at different temperatures and annealed at 900°C inoxygen are studied by photoluminescence (PL) and x-ray photoelectronspectroscopy (XPS). It is observed that in the PL of the as-grown films the green luminescence (GL) and the yellow luminescence (YL) are related, and after annealing the GL is restrained and the YL is enhanced. The O 1s XPS results also show the coexistence of oxygen vacancy (VO) and interstitial oxygen (Oi) before annealing and the quenching of the VO after annealing. By combining the two results it is deduced that the GL and YL are related to the VO and Oi defects, respectively.
 Select Experimental Hamiltonian Learning of an 11-Qubit Solid-State Quantum Spin Register P.-Y. Hou, L. He, F. Wang, X.-Z. Huang, W.-G. Zhang, X.-L. Ouyang, X. Wang, W.-Q. Lian, X.-Y. Chang, L.-M. Duan Chin. Phys. Lett.    2019, 36 (10): 100303 .   DOI: 10.1088/0256-307X/36/10/100303 Abstract   HTML   PDF (1448KB) Learning the Hamiltonian of a quantum system is indispensable for prediction of the system dynamics and realization of high fidelity quantum gates. However, it is a significant challenge to efficiently characterize the Hamiltonian which has a Hilbert space dimension exponentially growing with the system size. Here, we develop and implement an adaptive method to learn the effective Hamiltonian of an 11-qubit quantum system consisting of one electron spin and ten nuclear spins associated with a single nitrogen-vacancy center in a diamond. We validate the estimated Hamiltonian by designing universal quantum gates based on the learnt Hamiltonian and implementing these gates in the experiment. Our experimental result demonstrates a well-characterized 11-qubit quantum spin register with the ability to test quantum algorithms, and shows our Hamiltonian learning method as a useful tool for characterizing the Hamiltonian of the nodes in a quantum network with solid-state spin qubits.
 Select Quantum Scars in Microwave Dielectric Photonic Graphene Billiards Xiao Wang, Guo-Dong Wei Chin. Phys. Lett.    2020, 37 (1): 014201 .   DOI: 10.1088/0256-307X/37/1/014201 Abstract   HTML   PDF (2593KB) In the band structure of graphene, the dispersion relation is linear around a Dirac point at the corners of the Brillouin zone. The closed graphene system has proven to be the ideal model to investigate relativistic quantum chaos phenomena. The electromagnetic material photonic graphene (PG) and electronic graphene not only have the same structural symmetry, but also have the similar band structure. Thus, we consider a stadium shaped resonant cavity filled with PG to demonstrate the relativistic quantum chaos phenomenon by numerical simulation. It is interesting that the relativistic quantum scars not only are identified in the PG cavities, but also appear and disappear repeatedly. The wave vector difference between repetitive scars on the same orbit is analyzed and confirmed to follow the quantization rule. The exploration will not only demonstrate a visual simulation of relativistic quantum scars but also propose a physical system for observing valley-dependent relativistic quantum scars, which is helpful for further understanding of quantum chaos.
 Select Table-Like Large Magnetocaloric Effect in the Misch Metal $R$Si Compound Ruo-Shui Liu, Jun Liu, Li-Chen Wang, Zheng-Rui Li, Xiang Yu, Yan Mi, Qiao-Yan Dong, Kai Li, Dan-Li Li, Chen-Hui Lv, Li-Feng Liu, Shu-Li He Chin. Phys. Lett.    2020, 37 (1): 017501 .   DOI: 10.1088/0256-307X/37/1/017501 Abstract   HTML   PDF (971KB) Magnetic properties and the magnetocaloric effect (MCE) of the $R$Si ($R$ = Ce, Pr, Nd) compounds made of Misch metal (MM) are investigated. Two transitions are found at 12 K and 38 K. Field variation generated large MCE and two peaks are found in the magnetic entropy change ($\Delta S$) curves, which correspond to the two transition temperatures. The maximum values of the magnetic entropy changes ($\Delta S$) are found to be $-5.1$ J/(kg$\cdot$K) and $-9.3$ J/(kg$\cdot$K) for the field ranges of 0–2 T and 0–5 T, respectively. The large $\Delta S$ as well as ultra-low price of MM make (MM)Si a competitive magnetic refrigerant candidate for low temperature in Eriksson cycle.
 Select High-Temperature Permittivity and Data−Mining of Silicon Dioxide at GHz Band YUAN Jie, WEN Bo, HOU Zhi-Ling, LU Ming-Ming, CAO Wen-Qiang, BA Chuan, FANG Xiao-Yong, CAO Mao-Sheng Chin. Phys. Lett.    2012, 29 (2): 027701 .   DOI: 10.1088/0256-307X/29/2/027701 Abstract   PDF (585KB) The high-temperature permittivity of quartz fibre-reinforced silicon dioxide (SiO2/SiO2) nano−composites is studied on the basis of the multi-scale theoretical model. We obtain the permittivity of the SiO2/SiO2 at high temperature, which is dependent on the temperature by data−mining. The result shows that the permittivity and loss tangent obtained by data-mining are well consistent with the measured ones. The high-temperature permittivity can be well predicted for SiO2/SiO2 by the as-proposed model and the data-mining method.