Table of contents

    05 January 2020, Volume 29 Issue 1 Previous issue    Next issue
    TOPICAL REVIEW—Strong-field atomic and molecular physics
    Bohmian trajectory perspective on strong field atomic processes
    Xuan-Yang Lai(赖炫扬), Xiao-Jun Liu(柳晓军)
    Chin. Phys. B, 2020, 29 (1):  013205.  DOI: 10.1088/1674-1056/ab5c0f
    Abstract ( 256 )   HTML   PDF (1701KB) ( 317 )  
    The interaction of an atom with an intense laser field provides an important approach to explore the ultrafast electron dynamics and extract the information of the atomic and molecular structures with unprecedented attosecond temporal and angstrom spatial resolution. To well understand the strong field atomic processes, numerous theoretical methods have been developed, including solving the time-dependent Schrödinger equation (TDSE), classical and semiclassical trajectory method, quantum S-matrix theory within the strong-field approximation, etc. Recently, an alternative and complementary quantum approach, called Bohmian trajectory theory, has been successfully used in the strong-field atomic physics and an exciting progress has been achieved in the study of strong-field phenomena. In this paper, we provide an overview of the Bohmian trajectory method and its perspective on two strong field atomic processes, i.e., atomic and molecular ionization and high-order harmonic generation, respectively.
    Review on non-dipole effects in ionization and harmonic generation of atoms and molecules
    Mu-Xue Wang(王慕雪), Si-Ge Chen(陈思格), Hao Liang(梁昊), Liang-You Peng(彭良友)
    Chin. Phys. B, 2020, 29 (1):  013302.  DOI: 10.1088/1674-1056/ab5c10
    Abstract ( 202 )   HTML   PDF (2540KB) ( 398 )  
    In this review, we will focus on recent progress on the investigations of nondipole effects in few-electron atoms and molecules interacting with light fields. We first briefly survey several popular theoretical methods and relevant concepts in strong field and attosecond physics beyond the dipole approximation. Physical phenomena stemming from the breakdown of the dipole approximation are then discussed in various topics, including the radiation pressure and photon-momentum transfer, the atomic stabilization, the dynamic interference, and the high-order harmonic generation. Whenever available, the corresponding experimental observations of these nondipole effects are also introduced respectively in each topics.
    TOPICAL REVIEW—Fundamental research under high magnetic fields
    Specific heat in superconductors
    Hai-Hu Wen(闻海虎)
    Chin. Phys. B, 2020, 29 (1):  017401.  DOI: 10.1088/1674-1056/ab5a3d
    Abstract ( 287 )   HTML   PDF (6693KB) ( 382 )  
    Specific heat is a powerful tool to investigate the physical properties of condensed materials. Superconducting state is achieved through the condensation of paired electrons, namely, the Cooper pairs. The condensed Cooper pairs have lower entropy compared with that of electrons in normal metal, thus specific heat is very useful in detecting the low lying quasiparticle excitations of the superconducting condensate and the pairing symmetry of the superconducting gap. In this brief overview, we will give an introduction to the specific heat investigation of the physical properties of superconductors. We show the data obtained in cuprate and iron based superconductors to reveal the pairing symmetry of the order parameter.
    TOPICAL REVIEW—Advanced calculation & characterization of energy storage materials & devices at multiple scale
    Neutron-based characterization techniques for lithium-ion battery research
    Enyue Zhao(赵恩岳), Zhi-Gang Zhang(张志刚), Xiyang Li(李西阳), Lunhua He(何伦华), Xiqian Yu(禹习谦), Hong Li(李泓), Fangwei Wang(王芳卫)
    Chin. Phys. B, 2020, 29 (1):  018201.  DOI: 10.1088/1674-1056/ab5d07
    Abstract ( 230 )   HTML   PDF (7218KB) ( 154 )  
    During the past decades, Li-ion batteries have been one of the most important energy storage devices. Large-scale energy storage requires Li-ion batteries which possess high energy density, low cost, and high safety. Other than advanced battery materials, in-depth understanding of the intrinsic mechanism correlated with cell reaction is also essential for the development of high-performance Li-ion battery. Advanced characterization techniques, especially neutron-based techniques, have greatly promoted Li-ion battery researches. In this review, the characteristics or capabilities of various neutron-based characterization techniques, including elastic neutron scattering, quasi-elastic neutron scattering, neutron imaging, and inelastic neutron scattering, for the related Li-ion-battery researches are summarized. The design of in-situ/operando environment is also discussed. The comprehensive survey on neutron-based characterizations for mechanism understanding will provide guidance for the further study of high-performance Li-ion batteries.
    SPECIAL TOPIC—Advanced calculation & characterization of energy storage materials & devices at multiple scale
    Photon-in/photon-out endstation for studies of energy materials at beamline 02B02 of Shanghai Synchrotron Radiation Facility
    Guoxi Ren(任国玺), Nian Zhang(张念), Xuefei Feng(冯雪飞), Hui Zhang(章辉), Pengfei Yu(于鹏飞), Shun Zheng(郑顺), Deng Zhou(周櫈), Zongwang Tian(田宗旺), Xiaosong Liu(刘啸嵩)
    Chin. Phys. B, 2020, 29 (1):  016101.  DOI: 10.1088/1674-1056/ab5d04
    Abstract ( 121 )   HTML   PDF (2039KB) ( 83 )  
    A new photon-in/photon-out endstation at beamline 02B02 of the Shanghai Synchrotron Radiation Facility for studying the electronic structure of energy materials has been constructed and fully opened to users. The endstation has the capability to perform soft x-ray absorption spectroscopy in total electron yield and total fluorescence yield modes simultaneously. The photon energy ranges from 40 eV to 2000 eV covering the K-edge of most low Z-elements and the L-edge of 3d transition-metals. The new self-designed channeltron detector allows us to achieve good fluorescence signals at the low photon flux. In addition, we synchronously collect the signals of a standard reference sample and a gold mesh on the upstream to calibrate the photon energy and monitor the beam fluctuation, respectively. In order to cross the pressure gap, in situ gas and liquid cells for soft x-ray absorption spectroscopy are developed to study the samples under realistic working conditions.
    SPECIAL TOPIC—Topological semimetals
    Electronic structure of correlated topological insulator candidate YbB6 studied by photoemission and quantum oscillation
    T Zhang(张腾), G Li(李岗), S C Sun(孙淑翠), N Qin(秦娜), L Kang(康璐), S H Yao(姚淑华), H M Weng(翁红明), S K Mo, L Li(李璐), Z K Liu(柳仲楷), L X Yang(杨乐仙), Y L Chen(陈宇林)
    Chin. Phys. B, 2020, 29 (1):  017304.  DOI: 10.1088/1674-1056/ab6206
    Abstract ( 220 )   HTML   PDF (1772KB) ( 187 )  
    Angle-resolved photoemission spectroscopy (ARPES) and torque magnetometry (TM) measurements have been carried out to study the electronic structures of a correlated topological insulator (TI) candidate YbB6. We observed clear surface states on the [001] surface centered at the Γ and M points of the surface Brillouin zone. Interestingly, the fermiology revealed by the quantum oscillation of TM measurements agrees excellently with ARPES measurements. Moreover, the band structures we observed suggest that the band inversion in YbB6 happens between the Yb5d and B2p bands, instead of the Yb5d and Yb4f bands as suggested by previous theoretical investigation, which will help settle the heavy debate regarding the topological nature of samarium/ytterbium hexaborides.
    SPECIAL TOPIC—Optical field manipulation
    Dynamic shaping of vectorial optical fields based on two-dimensional blazed holographic grating
    Xinyi Wang(王心怡), Yuan Gao(高源), Zhaozhong Chen(陈召忠), Jianping Ding(丁剑平), Hui-Tian Wang(王慧田)
    Chin. Phys. B, 2020, 29 (1):  014208.  DOI: 10.1088/1674-1056/ab5a3b
    Abstract ( 178 )   HTML   PDF (2767KB) ( 115 )  
    We propose a vectorial optical field generation system based on two-dimensional blazed grating to high-efficiently generate structured optical fields with prescribed amplitude, phase, and polarization. In this system, an optimized blazed grating hologram is written on a spatial light modulator (SLM) and can diffract the majority of the incident light into the first-order diffractions of the x and y directions, which then serve as base vectors for synthesizing desired vector beams. Compared with the conventional cosine grating used in the previous work, the proposed two-dimensional, blazed grating has a much higher efficiency. Both computer simulation and optical experiment validate that a conversion efficiency up to 5 times that of the former work is achieved. Our method can facilitate applications of the optical field manipulation.
    SPECIAL TOPIC—High-throughput screening and design of optoelectronic materials
    High-throughput fabrication and semi-automated characterization of oxide thin film transistors
    Yanbing Han(韩炎兵), Sage Bauers, Qun Zhang(张群), Andriy Zakutayev
    Chin. Phys. B, 2020, 29 (1):  018502.  DOI: 10.1088/1674-1056/ab5d05
    Abstract ( 130 )   HTML   PDF (4344KB) ( 120 )  
    High throughput experimental methods are known to accelerate the rate of research, development, and deployment of electronic materials. For example, thin films with lateral gradients in composition, thickness, or other parameters have been used alongside spatially-resolved characterization to assess how various physical factors affect the material properties under varying measurement conditions. Similarly, multi-layer electronic devices that contain such graded thin films as one or more of their layers can also be characterized spatially in order to optimize the performance. In this work, we apply these high throughput experimental methods to thin film transistors (TFTs), demonstrating combinatorial channel layer growth, device fabrication, and semi-automated characterization using sputtered oxide TFTs as a case study. We show that both extrinsic and intrinsic types of device gradients can be generated in a TFT library, such as channel thickness and length, channel cation compositions, and oxygen atmosphere during deposition. We also present a semi-automated method to measure the 44 devices fabricated on a 50 mm×50 mm substrate that can help to identify properly functioning TFTs in the library and finish the measurement in a short time. Finally, we propose a fully automated characterization system for similar TFT libraries, which can be coupled with high throughput data analysis. These results demonstrate that high throughput methods can accelerate the investigation of TFTs and other electronic devices.
    Attosecond pulse trains driven by IR pulses spectrally broadened via supercontinuum generation in solid thin plates
    Yu-Jiao Jiang(江昱佼), Yue-Ying Liang(梁玥瑛), Yi-Tan Gao(高亦谈), Kun Zhao(赵昆), Si-Yuan Xu(许思源), Ji Wang(王佶), Xin-Kui He(贺新奎), Hao Teng(滕浩), Jiang-Feng Zhu(朱江峰), Yun-Lin Chen(陈云琳), Zhi-Yi Wei(魏志义)
    Chin. Phys. B, 2020, 29 (1):  013206.  DOI: 10.1088/1674-1056/ab6315
    Abstract ( 155 )   HTML   PDF (1233KB) ( 162 )  
    We utilized a set of fused silica thin plates to broaden the spectrum of 1 kHz, 30 fs Ti:sapphire amplified laser pulses to an octave. Following the compression by chirped mirror pairs, the generated few-cycle pulses were focused onto an argon filled gas cell. We detected high order harmonics corresponding to a train of 209 as pulses, characterized by the reconstruction of attosecond beating by interference of two-photon transition (RABITT) technique. Compared with the conventional attosecond pulse trains, the broad harmonics in such pulse trains cover more energy range, so it is more efficient in studying some typical cases, such as resonances, with frequency resolved RABITT. As the solid thin plates can support high power supercontinuum generation, it is feasible to tailor the spectrum to have different central wavelength and spectral width, which will make the RABITT source work in different applications.
    Supersonic boundary layer transition induced by self-sustaining dual jets
    Qiang Liu(刘强), Zhenbing Luo(罗振兵), Xiong Deng(邓雄), Zhiyong Liu(刘志勇), Lin Wang(王林), Yan Zhou(周岩)
    Chin. Phys. B, 2020, 29 (1):  014704.  DOI: 10.1088/1674-1056/ab5ef7
    Abstract ( 114 )   HTML   PDF (10375KB) ( 89 )  
    To promote high-speed boundary layer transition, this paper proposes an active self-sustaining dual jets (SDJ) actuator utilizing the energy of supersonic mainflow. Employing the nanoparticle-based planar laser scattering (NPLS), supersonic flat-plate boundary layer transition induced by SDJ is experimentally investigated in an Ma-2.95 low-turbulence wind tunnel. Streamwise and spanwise NPLS images are obtained to analyze fine flow structures of the whole transition process. The results reveal the transition control mechanisms that on the one hand, the jet-induced shear layer produces unstable Kelvin-Helmholtz instabilities in the wake flow, on the other hand, the jets also generates an adverse pressure gradient in the boundary layer and induce unstable streak structures, which gradually break down into turbulence downstream. The paper provides a new method for transition control of high-speed boundary layer, and have prospect both in theory and engineering application.
    Epitaxial growth and air-stability of monolayer Cu2Te Hot!
    K Qian(钱凯), L Gao(高蕾), H Li(李航), S Zhang(张帅), J H Yan(严佳浩), C Liu(刘晨), J O Wang(王嘉鸥), T Qian(钱天), H Ding(丁洪), Y Y Zhang(张余洋), X Lin(林晓), S X Du(杜世萱), H-J Gao(高鸿钧)
    Chin. Phys. B, 2020, 29 (1):  018104.  DOI: 10.1088/1674-1056/ab5781
    Abstract ( 311 )   HTML   PDF (1491KB) ( 237 )  
    A new two-dimensional atomic crystal, monolayer cuprous telluride (Cu2Te) has been fabricated on a graphene-SiC(0001) substrate by molecular beam epitaxy (MBE). The low-energy electron diffraction (LEED) characterization shows that the monolayer Cu2Te forms a √3×√3 superstructure with respect to the graphene substrate. The atomic structure of the monolayer Cu2Te is investigated through a combination of scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations. The stoichiometry of the Cu2Te sample is verified by x-ray photoelectron spectroscopy (XPS) measurement. The angle-resolved photoemission spectroscopy (ARPES) data present the electronic band structure of the sample, which is in good agreement with the calculated results. Furthermore, air-exposure experiments reveal the chemical stability of the monolayer Cu2Te. The fabrication of this new 2D material with a particular structure may bring new physical properties for future applications.
    Visualization of tunnel magnetoresistance effect in single manganite nanowires Hot!
    Yang Yu(郁扬), Wenjie Hu(胡雯婕), Qiang Li(李强), Qian Shi(时倩), Yinyan Zhu(朱银燕), Hanxuan Lin(林汉轩), Tian Miao(苗田), Yu Bai(白羽), Yanmei Wang(王艳梅), Wenting Yang(杨文婷), Wenbin Wang(王文彬), Hangwen Guo(郭杭闻), Lifeng Yin(殷立峰), Jian Shen(沈健)
    Chin. Phys. B, 2020, 29 (1):  018501.  DOI: 10.1088/1674-1056/ab5932
    Abstract ( 218 )   HTML   PDF (675KB) ( 150 )  
    We reported a study of tunnel magnetoresistance (TMR) effect in single manganite nanowire via the combination of magnetotransport and magnetic force microscopy imaging. TMR value up to 290% has been observed in single (La1-yPry)1-xCaxMnO3 nanowires with varying width. We find that the TMR effect can be explained in the scenario of opening and blockade of conducting channels from inherent magnetic domain evolutions. Our findings provide a new route to fabricate TMR junctions and point towards future improvements in complex oxide-based TMR spintronics.
    Quantum intelligence on protein folding pathways Hot!
    Wen-Wen Mao(毛雯雯), Li-Hua Lv(吕丽花), Yong-Yun Ji(季永运), You-Quan Li(李有泉)
    Chin. Phys. B, 2020, 29 (1):  018702.  DOI: 10.1088/1674-1056/ab5fbe
    Abstract ( 247 )   HTML   PDF (1526KB) ( 105 )  
    We study the protein folding problem on the base of our quantum approach by considering the model of protein chain with nine amino-acid residues. We introduce the concept of distance space and its projections on a XY-plane, and two characteristic quantities, one is called compactness of protein structure and another is called probability ratio involving shortest path. The concept of shortest path enables us to reduce the 388×388 density matrix to a 2×2 one from which the von Neumann entropy reflecting certain quantum coherence feature is naturally defined. We observe the time evolution of average distance and compactness solved from the classical random walk and quantum walk, we also compare the features of the time-dependence of Shannon entropy and von Neumann entropy. All the results not only reveal the fast quantum folding time but also unveil the existence of quantum intelligence hidden behind in choosing protein folding pathways.
    Coherence measures based on sandwiched Rényi relative entropy
    Jianwei Xu(胥建卫)
    Chin. Phys. B, 2020, 29 (1):  010301.  DOI: 10.1088/1674-1056/ab5930
    Abstract ( 140 )   HTML   PDF (345KB) ( 105 )  
    Coherence is a fundamental ingredient for quantum physics and a key resource for quantum information theory. Baumgratz, Cramer and Plenio established a rigorous framework (BCP framework) for quantifying coherence[Baumgratz T, Cramer M and Plenio M B Phys. Rev. Lett. 113 140401 (2014)]. In the present paper, under the BCP framework we provide two classes of coherence measures based on the sandwiched Rényi relative entropy. We also prove that we cannot get a new coherence measure f(C(·)) by a function f acting on a given coherence measure C.
    A new way to construct topological invariants of non-Hermitian systems with the non-Hermitian skin effect
    J S Liu(刘建森), Y Z Han(韩炎桢), C S Liu(刘承师)
    Chin. Phys. B, 2020, 29 (1):  010302.  DOI: 10.1088/1674-1056/ab5937
    Abstract ( 148 )   HTML   PDF (560KB) ( 206 )  
    The non-Hermitian skin effect breaks the conventional bulk-boundary correspondence and leads to non-Bloch topological invariants. Inspired by the fact that the topological protected zero modes are immune to perturbations, we construct a partner of a non-Hermitian system by getting rid of the non-Hermitian skin effect. Through adjusting the imbalance hopping, we find that the existence of zero-energy boundary states still dictate the bulk topological invariants based on the band-theory framework. Two non-Hermitian Su-Schrieffer-Heeger (SSH) models are used to illuminate the ideas. Specially, we obtain the winding numbers in analytical form without the introduction of the generalized Brillouin zone. The work gives an alternative method to calculate the topological invariants of non-Hermitian systems.
    Landau-like quantized levels of neutral atom induced by a dark-soliton shaped electric field
    Yueming Wang(王月明), Zhen Jin(靳祯)
    Chin. Phys. B, 2020, 29 (1):  010303.  DOI: 10.1088/1674-1056/ab5938
    Abstract ( 171 )   HTML   PDF (340KB) ( 94 )  
    Motivated by the fascinating progresses in the cold atom experiments and theories, especially the artificial gauge field induced spin-orbit coupling of neutral atoms, we present a novel dispersion of neutral atoms carrying a non-vanishing magnetic moment in a special gauge field, an external electric field of dark-soliton shaped profile. By means of WKB approximation, we obtain discrete quantized landau-like energy levels, which is instructive for the quantum Hall effect of neutral particles. The observability of the results is also discussed.
    Fault tolerant controlled quantum dialogue against collective noise
    Li-Wei Chang(常利伟), Yu-Qing Zhang(张宇青), Xiao-Xiong Tian(田晓雄), Yu-Hua Qian(钱宇华), Shi-Hui Zheng(郑世慧)
    Chin. Phys. B, 2020, 29 (1):  010304.  DOI: 10.1088/1674-1056/ab5786
    Abstract ( 149 )   HTML   PDF (462KB) ( 107 )  
    Quantum system is inevitably affected by the external environment in the real world. Two controlled quantum dialogue protocols are put forward based on logical χ-type states under collective noise environment. One is against collective-dephasing noise, while the other is against collective-rotation noise. Compared with existing protocols, there exist several outstanding advantages in our proposed protocols:Firstly, the χ-type state is utilized as quantum channels, it possesses better entanglement properties than GHZ state, W state as well as cluster state, which make it difficult to be destroyed by local operations. Secondly, two kinds of logical χ-type states are constructed by us in theory, which can be perfectly immune to the effects of collective noise. Thirdly, the controller can be offline after quantum distribution and permission announcement, without waiting for all the participants to complete the information coding. Fourthly, the security analysis illuminates that our protocols can not only be free from the information leakage, but also resist against the intercept-and-resend attack, the entanglement-and-measure attack, the modification attack, the conspiring attack, and especially the dishonest controller's attacks.
    Heralded entanglement purification protocol using high-fidelity parity-check gate based on nitrogen-vacancy center in optical cavity
    Lu-Cong Lu(陆路聪), Guan-Yu Wang(王冠玉), Bao-Cang Ren(任宝藏), Mei Zhang(章梅), Fu-Guo Deng(邓富国)
    Chin. Phys. B, 2020, 29 (1):  010305.  DOI: 10.1088/1674-1056/ab5939
    Abstract ( 174 )   HTML   PDF (786KB) ( 132 )  
    The decoherence of entangled states caused by the noisy channel is a salient problem for reducing the fidelity of quantum communication. Here we present a heralded two-photon entanglement purification protocol (EPP) using heralded high-fidelity parity-check gate (HH-PCG), which can increase the entanglement of nonlocal two-photon polarization mixed state. The HH-PCG is constructed by the input-output process of nitrogen-vacancy (NV) center in diamond embedded in a single-sided optical cavity, where the errors caused by the imperfect interaction between the NV center-cavity system and the photon can be heralded by the photon detector. As the unwanted components can be filtrated due to the heralded function, the fidelity of the EPP scheme can be enhanced considerably, which will increase the fidelity of quantum communication processing.
    Collapses-revivals phenomena induced by weak magnetic flux in diamond chain
    Na-Na Chang(常娜娜), Wen-Quan Jing(景文泉), Yu Zhang(张钰), Ai-Xia Zhang(张爱霞), Ju-Kui Xue(薛具奎), Su-Peng Kou(寇谡鹏)
    Chin. Phys. B, 2020, 29 (1):  010306.  DOI: 10.1088/1674-1056/ab6087
    Abstract ( 106 )   HTML   PDF (2592KB) ( 102 )  
    We investigate the quantum dynamical behaviors of bosons in a diamond chain with weak magnetic flux (WMF), including Landau-Zener tunnelling, Bloch oscillations, localization phenomenon, and collapses-revivals phenomena. We observed that collapses-revivals phenomena can occur in diamond chain with WMF and cannot exist in the strong magnetic flux case as the previous study (Chang N N and Xue J K, 2018, Chin. Phys. B 27 105203). Induced by WMF, the energy band for the system varies from gapless to gapped structure. The position of the extrema of probability amplitude for ground state can also be altered by WMF within a single diamond plaquette. As a consequence, the transitions between different dynamical behaviors of bosons in diamond chain can be manipulated by WMF, depending on its initial configurations.
    Cyclotron dynamics of neutral atoms in optical lattices with additional magnetic field and harmonic trap potential
    Ai-Xia Zhang(张爱霞), Ying Zhang(张莹), Yan-Fang Jiang(姜艳芳), Zi-Fa Yu(鱼自发), Li-Xia Cai(蔡丽霞), Ju-Kui Xue(薛具奎)
    Chin. Phys. B, 2020, 29 (1):  010307.  DOI: 10.1088/1674-1056/ab5efc
    Abstract ( 117 )   HTML   PDF (2997KB) ( 66 )  
    We analytically and numerically discuss the stability and dynamics of neutral atoms in a two-dimensional optical lattice subjected to an additional harmonic trap potential and artificial magnetic field. The harmonic trap potential plays a key role in modifying the equilibrium state properties of the system and stabilizing the cyclotron orbits of the condensate. Meanwhile, the presence of the harmonic trap potential and lattice potential results in rich cyclotron dynamics of the condensate. The coupling effects of lattice potential, artificial magnetic field, and harmonic trap potential lead to single periodic, multi-periodic or quasi-periodic cyclotron orbits of the condensate. So we can control the cyclotron dynamics of neutral atoms in optical lattice by manipulating the strength of harmonic confinement, artificial magnetic field, and initial conditions. Our results provide a direct theoretical evidence for the cyclotron dynamics of neutral atoms in optical lattices exposed to the artificial gauge magnetic field and harmonic trap potential.
    Quantum adiabatic algorithms using unitary interpolation
    Shuo Zhang(张硕), Qian-Heng Duan(段乾恒), Tan Li(李坦), Xiang-Qun Fu(付向群), He-Liang Huang(黄合良), Xiang Wang(汪翔), Wan-Su Bao(鲍皖苏)
    Chin. Phys. B, 2020, 29 (1):  010308.  DOI: 10.1088/1674-1056/ab5f02
    Abstract ( 109 )   HTML   PDF (409KB) ( 95 )  
    We present two efficient quantum adiabatic algorithms for Bernstein-Vazirani problem and Simon's problem. We show that the time complexities of the algorithms for Bernstein-Vazirani problem and Simon's problem are O(1) and O(n), respectively, which are the same complexities as the corresponding algorithms in quantum circuit model. In these two algorithms, the adiabatic Hamiltonians are realized by unitary interpolation instead of standard linear interpolation. Comparing with the adiabatic algorithms using linear interpolation, the energy gaps of our algorithms keep constant. Therefore, the complexities are much easier to analyze using this method.
    Analyzing floor-stair merging flow based on experiments and simulation
    Yu Zhu(朱萸), Tao Chen(陈涛), Ning Ding(丁宁), Wei-Cheng Fan(范维澄)
    Chin. Phys. B, 2020, 29 (1):  010401.  DOI: 10.1088/1674-1056/ab5788
    Abstract ( 119 )   HTML   PDF (645KB) ( 99 )  
    In most situations, staircase is the only egress to evacuate from high-rise buildings. The merging flow on the stair landing has a great influence on the evacuation efficiency. In this paper, we develop an improved cellular automaton model to describe the merging behavior, and the model is validated by a series of real experiments. It is found that the flow rate of simulation results is similar to the drills, which means that the improved model is reasonable and can be used to describe the merging behavior on stairs. Furthermore, some scenarios with different door locations and building floor numbers are simulated by the model. The results show that (i) the best door location is next to the upward staircase; (ii) the total evacuation time and the building floor number are linearly related to each other; (iii) the pedestrians on upper floors have a negative influence on the evacuation flow rate.
    Fluctuation theorem for entropy production at strong coupling
    Y Y Xu(徐酉阳), J Liu(刘娟), M Feng(冯芒)
    Chin. Phys. B, 2020, 29 (1):  010501.  DOI: 10.1088/1674-1056/ab592d
    Abstract ( 131 )   HTML   PDF (353KB) ( 88 )  
    Fluctuation theorems have been applied successfully to any system away from thermal equilibrium, which are helpful for understanding the thermodynamic state evolution. We investigate fluctuation theorems for strong coupling between a system and its reservoir, by path-dependent definition of work and heat satisfying the first law of thermodynamics. We present the fluctuation theorems for two kinds of entropy productions. One is the informational entropy production, which is always non-negative and can be employed in either strong or weak coupling systems. The other is the thermodynamic entropy production, which differs from the informational entropy production at strong coupling by the effects regarding the reservoir. We find that, it is the negative work on the reservoir, rather than the nonequilibrium of the thermal reservoir, which invalidates the thermodynamic entropy production at strong coupling. Our results indicate that the effects from the reservoir are essential to understanding thermodynamic processes at strong coupling.
    Microfluidic temperature sensor based on temperature-dependent dielectric property of liquid
    Qi Liu(刘琦), Yu-Feng Yu(俞钰峰), Wen-Sheng Zhao(赵文生), Hui Li(李慧)
    Chin. Phys. B, 2020, 29 (1):  010701.  DOI: 10.1088/1674-1056/ab593c
    Abstract ( 173 )   HTML   PDF (950KB) ( 77 )  
    We propose a low-cost compact microfluidic temperature sensor by virtue of the temperature-dependent permittivity of liquid. The sensor is composed of a coplanar waveguide (CPW) transmission line loaded with three resonators and a microfluidic plate with three channels. The resonant frequency of each resonator relies on the temperature-dependent dielectric property of liquid in corresponding channel, which therefore can be used to extract the temperature. The proposed sensor features a compact size and low cost since it requires only micro fluid volume instead of additional electronic components to produce significant frequency shift with changing temperature. Moreover, it exhibits decent accuracy and stability in a temperature sensing range from 30 ^oC to 95 ^oC. A theoretical analysis of the sensor is provided, followed by the detailed characterization method, and a prototype is designed, manufactured, and measured to verify the theoretical analysis.
    A new technology for controlling in-situ oxygen fugacity in diamond anvil cells and measuring electrical conductivity of anhydrous olivine at high pressures and temperatures
    Wen-Shu Shen(沈文舒), Lei Wu(吴雷), Tian-Ji Ou(欧天吉), Dong-Hui Yue(岳冬辉), Ting-Ting Ji(冀婷婷), Yong-Hao Han(韩永昊), Wen-Liang Xu(许文良), Chun-Xiao Gao(高春晓)
    Chin. Phys. B, 2020, 29 (1):  010702.  DOI: 10.1088/1674-1056/ab5934
    Abstract ( 97 )   HTML   PDF (1958KB) ( 89 )  
    We present a novel technique for controlling oxygen fugacity, which is broadly used to in-situ measure the electrical conductivities in minerals and rocks during diamond anvil cell experiments. The electrical conductivities of olivine are determined under controlled oxygen fugacity conditions (Mo-MoO2) at pressures up to 4.0 GPa and temperatures up to 873 K. The advantages of this new technique enable the measuring of the activation enthalpy, activation energy, and activation bulk volume in the Arrhenius relationship. This provides an improved understanding of the mechanism of conduction in olivine. Electrical conduction in olivine is best explained by small polaron movement, given the oxygen fugacity-dependent variations in conductivity.
    Low temperature photoluminescence study of GaAs defect states
    Jia-Yao Huang(黄佳瑶), Lin Shang(尚林), Shu-Fang Ma(马淑芳), Bin Han(韩斌), Guo-Dong Wei(尉国栋), Qing-Ming Liu(刘青明), Xiao-Dong Hao(郝晓东), Heng-Sheng Shan(单恒升), Bing-She Xu(许并社)
    Chin. Phys. B, 2020, 29 (1):  010703.  DOI: 10.1088/1674-1056/ab5fb8
    Abstract ( 142 )   HTML   PDF (956KB) ( 110 )  
    Low temperature (77 K) photoluminescence measurements have been performed on different GaAs substrates to evaluate the GaAs crystal quality. Several defect-related luminescence peaks have been observed, including 1.452 eV, 1.476 eV, 1.326 eV peaks deriving from 78 meV GaAs antisite defects, and 1.372 eV, 1.289 eV peaks resulting from As vacancy related defects. Changes in photoluminescence emission intensity and emission energy as a function of temperature and excitation power lead to the identification of the defect states. The luminescence mechanisms of the defect states were studied by photoluminescence spectroscopy and the growth quality of GaAs crystal was evaluated.
    Atmospheric N2O gas detection based on an inter-band cascade laser around 3.939 μm
    Chun-Yan Sun(孙春艳), Yuan Cao(曹渊), Jia-Jin Chen(陈家金), Jing-Jing Wang(王静静), Gang Cheng(程刚), Gui-Shi Wang(王贵师), Xiao-Ming Gao(高晓明)
    Chin. Phys. B, 2020, 29 (1):  010704.  DOI: 10.1088/1674-1056/ab5ef6
    Abstract ( 110 )   HTML   PDF (894KB) ( 109 )  
    N2O is a significant atmospheric greenhouse gas that contributes to global warming and climate change. In this work, the high sensitivity detection of atmospheric N2O is achieved using wavelength modulation spectroscopy (WMS) with an inter-band cascade laser operating around 3.939 μm. A LabVIEW-based software signal generator and software lock-in amplifiers are designed to simplify the system. In order to eliminate the interference from water vapor, the detection was performed at a pressure of 0.1 atm (1 atm=1.01325×105 Pa) and a drying tube was added to the system. To improve the system performance for long term detection, a novel frequency locking method and 2f/1f calibration-free method were employed to lock the laser frequency and calibrate the power fluctuations, respectively. The Allan deviation analysis of the results indicates a detection limit of ~20 ppb (1 ppb=1.81205 μg/m3) for a 1 s integration time, and the optimal detection limit is ~5 ppb for a 40-s integration time.
    Study of highly excited vibrational dynamics of HCP integrable system with dynamic potential methods
    Aixing Wang(王爱星), Lifeng Sun(孙立风), Chao Fang(房超), Yibao Liu(刘义保)
    Chin. Phys. B, 2020, 29 (1):  013101.  DOI: 10.1088/1674-1056/ab593a
    Abstract ( 126 )   HTML   PDF (3734KB) ( 55 )  
    Highly excited vibrational dynamics of phosphaethyne (HCP) integrable system are investigated based on its dynamic potentials. Taking into consideration the 2:1 Fermi resonance between H-C-P bending vibrational mode and C-P stretching vibrational mode, it is found that the effects of H-C stretching vibrational mode on vibrational dynamic features of the HCP integrable system are significant and regularly vary with Polyad numbers (P number). The geometrical profiles of the dynamic potentials and the corresponding fixed points are sensitive to the variation of H-C stretching vibrational strength when P numbers are small, but are not sensitive when P numbers become larger and the corresponding threshold values become lower. The phase space trajectories of different energy levels in a designated dynamic potential (P=28) were studied and the results indicated that the dynamic potentials govern the various dynamic environments in which the vibrational states lie. Furthermore, action integrals of the energy levels contained in dynamic potential (P=28) were quantitatively analyzed and elucidated. It was determined that the dynamic environments could be identified by the numerical values of the action integrals of trajectories of phase space, which is equivalent with dynamic potentials.
    Benchmarking PBE+D3 and SCAN+rVV10 methods using potential energy surfaces generated with MP2+ ΔCCSD(T) calculation Hot!
    Jie Chen(陈劼), Weiyu Xie(谢炜宇), Kaihang Li(李开航), Shengbai Zhang(张绳百), Yi-Yang Sun(孙宜阳)
    Chin. Phys. B, 2020, 29 (1):  013102.  DOI: 10.1088/1674-1056/ab5fbb
    Abstract ( 295 )   HTML   PDF (714KB) ( 139 )  
    We develop a benchmark system for van der Waals interactions obtained with MP2+ΔCCSD(T) method at complete basis set limit. With this benchmark, we examine the widely used PBE+D3 method and recently developed SCAN+rVV10 method for density functional theory calculations. Our benchmark is based on two molecules:glycine (or Gly, an amino acid) and uracil (or U, an RNA base). We consider six dimer configurations of the two monomers and their potential energy surfaces as a function of relative distance and rotation angle. The Gly-Gly, Gly-U, and U-U pairs represent London dispersion, hydrogen bonding, and π-π stacking interactions, respectively. Our results show that both PBE+D3 and SCAN+rVV10 methods can yield accuracy better than 1 kcal/mol, except for the cases when the distance between the two monomers is significantly smaller than the equilibrium distance. In such a case, neither of these methods can yield uniformly accurate results for all the configurations. In addition, it is found that the SCAN and SCAN+rVV10 methods can reproduce some subtle features in a rotational potential energy curve, while the PBE, PBE+D3, and the local density approximation fail.
    Highly sensitive detection of Rydberg atoms with fluorescence loss spectrum in cold atoms
    Xuerong Shi(师雪荣), Hao Zhang(张好), Mingyong Jing(景明勇), Linjie Zhang(张临杰), Liantuan Xiao(肖连团), Suotang Jia(贾锁堂)
    Chin. Phys. B, 2020, 29 (1):  013201.  DOI: 10.1088/1674-1056/ab593b
    Abstract ( 121 )   HTML   PDF (1087KB) ( 106 )  
    Fluorescence loss spectrum for detecting cold Rydberg atoms with high sensitivity has been obtained based on lock-in detection of fluorescence of 6P3/2 state when cooling lasers of the magneto-optical trap are modulated. The experiment results show that the signal to noise ratio has been improved by 32.64 dB when the modulation depth (converted to laser frequency) and frequency are optimized to 4 MHz and 6 kHz, respectively. This technique enables us to perform a highly sensitive non-destructive detection of Rydberg atoms.
    Quantum interference of a time-dependent wave packet of atom irradiated by an ultra-short laser pulse
    Wen-Min Yan(闫文敏), Ji-Gen Chen(陈基根), Jun Wang(王俊), Fu-Ming Guo(郭福明), Yu-Jun Yang(杨玉军)
    Chin. Phys. B, 2020, 29 (1):  013202.  DOI: 10.1088/1674-1056/ab5a3c
    Abstract ( 143 )   HTML   PDF (2819KB) ( 119 )  
    The wave packet evolution of an atom irradiated by an intense laser pulse is systematically investigated by using the numerical solution of the time-dependent Schrödinger equation. There are two types of spatial interference structures in the time-dependent evolution of the atomic wave packet. With the increasing of the evolution time, the interference fringe spacing for type I (type II) becomes larger (smaller). As the wavelength of the incident laser increases, the interference of the wave packet is changed from type II to type I, and the shift of interference type can be attributed to the contribution of excited states by using the energy analysis of the time-dependent wave function.
    Relative phase effect of nonsequential double ionization in Ar by two-color elliptically polarized laser field
    Jia-He Chen(陈佳贺), Tong-Tong Xu(徐彤彤), Tao Han(韩涛), Yue Sun(孙悦), Qing-Yun Xu(徐清芸), Xue-Shen Liu(刘学深)
    Chin. Phys. B, 2020, 29 (1):  013203.  DOI: 10.1088/1674-1056/ab5d03
    Abstract ( 150 )   HTML   PDF (1458KB) ( 82 )  
    We investigated the nonsequential double ionization (NSDI) in Ar by two-color elliptically polarized laser field with a three-dimensional (3D) classical ensemble method. We study the relative phase effect of NSDI and distinguish two particular recollision channels in NSDI, which are recollision-impact ionization (RII) and recollision-induced excitation with subsequent ionization (RESI), according to the delay-time between the recollision and the final double ionization. The numerical results indicate that the ion momentum distribution is changed and the triangle structure is more obvious with the decrease of the relative phase. We also demonstrate that the RESI process always dominates in the whole double ionization process and the ratio of RESI and RII channels can be influenced by the relative phase.
    Tunable multistability and nonuniform phases in a dimerized two-dimensional Rydberg lattice
    Han-Xiao Zhang(张焓笑), Chu-Hui Fan(范楚辉), Cui-Li Cui(崔淬砺), Jin-Hui Wu(吴金辉)
    Chin. Phys. B, 2020, 29 (1):  013204.  DOI: 10.1088/1674-1056/ab5d06
    Abstract ( 98 )   HTML   PDF (2357KB) ( 122 )  
    We study the multistability of fixed points for a dimerized system of Rydberg atoms driven by two laser fields and trapped in a two-dimensional (2D) square lattice. For identical driving fields, the fixed points of this system exhibit stable uniform, unstable uniform, stable nonuniform, or oscillating nonuniform phases in the presence of a bistable region. For different driving fields, however, all (stable, unstable, or oscillating) phases become nonuniform instead, which then results in two islets isolated from the mainland of Rydberg excitation. We also show that a tristable region may stretch out from the (nonuniform) bistable region near the islets, indicating that a richer phase diagram can be attained by tuning the Rabi frequencies and/or detunings of the driving fields. Last but not least, the fixed points can adiabatically evolve from the islets to the mainland but can not inversely evolve from the mainland to the islets.
    Spectral attenuation of a 400-nm laser pulse propagating through a plasma filament induced by an intense femtosecond laser pulse
    Quan-Jun Wang(王全军), Rao Chen(陈娆), Jia-Chen Zhao(赵家琛), Chun-Lin Sun(孙春霖), Xiao-Zhen Wang(王小珍), Jing-Jie Ding(丁晶洁), Zuo-Ye Liu(刘作业), Bi-Tao Hu(胡碧涛)
    Chin. Phys. B, 2020, 29 (1):  013301.  DOI: 10.1088/1674-1056/ab5a39
    Abstract ( 136 )   HTML   PDF (646KB) ( 116 )  
    The spectral attenuation of a 400-nm probe laser propagating through a femtosecond plasma in air is studied. Defocusing effect of the low-density plasma is an obvious effect by examining the far-field patterns of the 400-nm pulse. Besides, the energy of 400-nm pulse drops after interaction with the plasma, which is found to be another effect leading to the attenuation. To reveal the physical origin behind the energy loss, we measure fluorescence emissions of the interaction area. The fluorescence is hardly detected with the weak 400-nm laser pulse, and the line spectra from the plasma filament induced by the 800-nm pump pulse are clearly shown. However, when the 400-nm pulse propagates through the plasma filament, the fluorescence at 391 nm from the first negative band system of N2+ is enhanced, while that from the second positive band of neutral N2 at 337 nm remains constant. Efficient near-resonant absorption of the 400-nm pulse by the first negative band system occurs inside the plasma, which results in the enhanced fluorescence. Furthermore, the spectral attenuation of the 400-nm probe laser is measured as a function of the pump-probe time delay as well as the pump-pulse energy.
    Electron capture in collisions of Li3+ ions with ground andexcited states of Li atoms
    M X Ma(马茗萱), B H Kou(寇博珩), L Liu(刘玲), Y Wu(吴勇), J G Wang(王建国)
    Chin. Phys. B, 2020, 29 (1):  013401.  DOI: 10.1088/1674-1056/ab577f
    Abstract ( 126 )   HTML   PDF (629KB) ( 64 )  
    The electron capture processes in collisions of Li3+ ion with Li(1s22s) and Li(1s22p0,1) are investigated by using the two-center atomic orbital close-coupling method in the energy range from 0.1 keV/u to 300 keV/u. The interaction of the active electrons with the target ion is represented by a model potential. The present results for the Li3+-Li(1s22s) system are compared with the available theoretical data and general agreement is obtained for the high collision energies. It is also found that the total and partial electron capture cross sections are sensitive to the initial charge cloud alignment in the low energy region.
    Broadband visible light absorber based on ultrathin semiconductor nanostructures
    Lin-Jin Huang(黄林锦), Jia-Qi Li(李嘉麒), Man-Yi Lu(卢漫仪), Yan-Quan Chen(陈彦权), Hong-Ji Zhu(朱宏基), Hai-Ying Liu(刘海英)
    Chin. Phys. B, 2020, 29 (1):  014201.  DOI: 10.1088/1674-1056/ab5787
    Abstract ( 121 )   HTML   PDF (1648KB) ( 124 )  
    It is desirable to have electromagnetic wave absorbers with ultrathin structural thickness and broader spectral absorption bandwidth with numerous applications in optoelectronics. In this paper, we theoretically propose and numerically demonstrate a novel ultrathin nanostructure absorber composed of semiconductor nanoring array and a uniform gold substrate. The results show that the absorption covers the entire visible light region, achieving an average absorption rate more than 90% in a wavelength range from 300 nm to 740 nm and a nearly perfect absorption from 450 nm to 500 nm, and the polarization insensitivity performance is particularly great. The absorption performance is mainly caused by the electrical resonance and magnetic resonance of semiconductor nanoring array as well as the field coupling effects. Our designed broadband visible light absorber has wide application prospects in the fields of thermal photovoltaics and photodetectors.
    Noise-like rectangular pulses in a mode-locked double-clad Er:Yb laser with a record pulse energy
    Tianyi Wu(吴田宜), Zhiyuan Dou(窦志远), Bin Zhang(张斌), Jing Hou(侯静)
    Chin. Phys. B, 2020, 29 (1):  014202.  DOI: 10.1088/1674-1056/ab578a
    Abstract ( 146 )   HTML   PDF (974KB) ( 95 )  
    Generation of noise-like rectangular pulse was investigated systematically in an Er-Yb co-doped fiber laser based on an intra-cavity coupler with different coupling ratios. When the coupling ratio was 5/95, stable mode-locked pulses could be obtained with the pulse packet duration tunable from 4.86 ns to 80 ns. The repetition frequency was 1.186 MHz with the output spectrum centered at 1.6 μ. The average output power and single pulse energy reached a record 1.43 W and 1.21 μJ, respectively. Pulse characteristics under different coupling ratios (5/95, 10/90, 20/80, 30/70, 40/60) were also presented and discussed.
    Propagation characteristics of parallel dark solitons in silicon-on-insulator waveguide
    Zhen Liu(刘振), Weiguo Jia(贾维国), Yang Wang(汪洋), Hongyu Wang(王红玉), Neimule Men-Ke(门克内木乐), Jun-Ping Zhang(张俊萍)
    Chin. Phys. B, 2020, 29 (1):  014203.  DOI: 10.1088/1674-1056/ab577d
    Abstract ( 122 )   HTML   PDF (4913KB) ( 81 )  
    The propagation characteristic of two identical and parallel dark solitons in a silicon-on-insulator (SOI) waveguide is simulated numerically using the split-step Fourier method. The parallel dark solitons imposed by the initial chirp are investigated mainly by changing their power, their relative time delay. The simulation shows that the time delay deforms the parallel dark soliton pulse, forming a bright-like soliton in the transmission process and making the transmission quality down. By increasing the power of one dark soliton, the energy of the other dark soliton can be increased, and larger increase in a soliton's power leads to larger increase in the energy of the other. When the initial chirp is introduced into one of the dark solitons, higher energy consumption is observed. In particular, positive chirps resulting in pulse broadening width while negative chirps narrowing, with an obvious compression effect on the other dark soliton. Finally, large negative chirps are found to have a profound impact on parallel and nonparallel dark solitons.
    Soliton evolution and control in a two-mode fiber with two-photon absorption
    Qianying Li(李倩颖)
    Chin. Phys. B, 2020, 29 (1):  014204.  DOI: 10.1088/1674-1056/ab5784
    Abstract ( 148 )   HTML   PDF (2007KB) ( 109 )  
    Soliton dynamics are numerically investigated in a two-mode fiber with the two-photon absorption, and the effects of the two-photon absorption on the soliton propagation and interaction are demonstrated in different dispersion regimes. Soliton dynamics depend strictly on the sign and magnitude of the group velocity dispersion (GVD) coefficient of each mode and the strength (coefficient) of the two-photon absorption. The two-photon absorption leads to the soliton collapse, enhances the neighboring soliton interaction in both modes, and increases the energy exchange between the two modes. Finally, an available control is proposed to suppress the effects by the use of the nonlinear gain with filter.
    Acquisition performance analysis for intersatellite optical communications with vibration influence
    Jing Ma(马晶), Gaoyuan Lu(陆高原), Siyuan Yu(于思源), Liying Tan(谭立英), Yulong Fu(付玉龙), Fajun Li(黎发军)
    Chin. Phys. B, 2020, 29 (1):  014205.  DOI: 10.1088/1674-1056/ab577e
    Abstract ( 106 )   HTML   PDF (474KB) ( 71 )  
    A stable and accurate pointing, acquisition system is an important part of initially building intersatellite optical communication links. Satellite platform vibration can cause the system instability and reduce the system precision in building and maintenance of a satellite optical communication system. In this paper, vibration influence is consciously discussed by acquisition time for intersatellite optical communications. Analytical expression of acquisition possibility is derived, taking the scan parameters and platform vibration into account, and vibration influence on the multi-scan acquisition time is also presented. The theoretical result calculated by the proposed analytical expression is approximate to the result by the Monte Carlo simulation.
    Unitary transformation of general nonoverlapping-image multimode interference couplers with any input and output ports
    Ze-Zheng Li(李泽正), Wei-Hua Han(韩伟华), Zhi-Yong Li(李智勇)
    Chin. Phys. B, 2020, 29 (1):  014206.  DOI: 10.1088/1674-1056/ab5783
    Abstract ( 95 )   HTML   PDF (857KB) ( 114 )  
    An explanation of optical unitary transformation is presented for general nonoverlapping-image multimode interference (MMI) couplers with any number of input and output ports. The light transformation in the MMI coupler can be considered as an optical field matrix acting on an input light column vector. We investigate the general phase principle of output light image. The complete proof of nonoverlapping-image MMI coupler's optical unitarity along with the phase analysis of matrix element is provided. Based on a two-dimensional finite-difference time-domain (2D-FDTD) simulation, the unitary transformation is obtained for a 4×4 nonoverlapping-image MMI coupler within a deviation of 4×10-2 for orthogonal invariance and 8×10-2 for transvection invariance in the C-band spectral range. A compact 1×4 splitter based on cascaded MMI coupler is proposed, showing a phase deviation less than 5.4° while maintaining a low-loss performance in C-band spectra.
    A novel particle tracking velocimetry method for complex granular flow field Hot!
    Bi-De Wang(王必得), Jian Song(宋健), Ran Li(李然), Ren Han(韩韧), Gang Zheng(郑刚), Hui Yang(杨晖)
    Chin. Phys. B, 2020, 29 (1):  014207.  DOI: 10.1088/1674-1056/ab5936
    Abstract ( 206 )   HTML   PDF (4750KB) ( 110 )  
    Particle tracking velocimetry (PTV) is one of the most commonly applied granular flow velocity measurement methods. However, traditional PTV methods may have issues such as high mismatching rates and a narrow measurement range when measuring granular flows with large bulk density and high-speed contrast. In this study, a novel PTV method is introduced to solve these problems using an optical flow matching algorithm with two further processing steps. The first step involves displacement correction, which is used to solve the mismatching problem in the case of high stacking density. The other step is trajectory splicing, which is used to solve the problem of a measurement range reduction in the case of high-speed contrast The hopper flow experimental results demonstrate superior performance of this proposed method in controlling the number of mismatched particles and better measuring efficiency in comparison with the traditional PTV method.
    Linear optical approach to supersymmetric dynamics
    Yong-Tao Zhan(詹颙涛), Xiao-Ye Xu(许小冶), Qin-Qin Wang(王琴琴), Wei-Wei Pan(潘维韦), Munsif Jan, Fu-Ming Chang(常弗鸣), Kai Sun(孙凯), Jin-Shi Xu(许金时), Yong-Jian Han(韩永建), Chuan-Feng Li(李传锋), Guang-Can Guo(郭光灿)
    Chin. Phys. B, 2020, 29 (1):  014209.  DOI: 10.1088/1674-1056/ab5efe
    Abstract ( 173 )   HTML   PDF (1129KB) ( 120 )  
    The concept of supersymmetry developed in particle physics has been applied to various fields of modern physics. In quantum mechanics, the supersymmetric systems refer to the systems involving two supersymmetric partner Hamiltonians, whose energy levels are degeneracy except one of the systems has an extra ground state possibly, and the eigenstates of the partner systems can be mapped onto each other. Recently, an interferometric scheme has been proposed to show this relationship in ultracold atoms[Phys. Rev. A 96 043624 (2017)]. Here this approach is generalized to linear optics for observing the supersymmetric dynamics with photons. The time evolution operator is simulated approximately via Suzuki-Trotter expansion with considering the realization of the kinetic and potential terms separately. The former is realized through the diffraction nature of light and the later is implemented using a phase plate. Additionally, we propose an interferometric approach which can be implemented perfectly using an amplitude alternator to realize the non-unitary operator. The numerical results show that our scheme is universal and can be realized with current technologies.
    Displacement damage in optocouplers induced by high energy neutrons at back-n in China Spallation Neutron Source
    Rui Xu(徐瑞), Zu-Jun Wang(王祖军), Yuan-Yuan Xue(薛院院), Hao Ning(宁浩), Min-Bo Liu(刘敏波), Xiao-Qiang Guo(郭晓强), Zhi-Bin Yao(姚志斌), Jiang-Kun Sheng(盛江坤), Wu-Ying Ma(马武英), Guan-Tao Dong(董观涛)
    Chin. Phys. B, 2020, 29 (1):  014210.  DOI: 10.1088/1674-1056/ab5efb
    Abstract ( 97 )   HTML   PDF (1272KB) ( 63 )  
    Neutron radiation experiments of optocouplers at back-streaming white neutrons (back-n) in China Spallation Neutron Source (CSNS) are presented. The displacement damages induced by neutron radiation are analyzed. The performance degradations of two types of optocouplers are compared. The degradations of current transfer ratio (CTR) are analyzed, and the mechanisms induced by radiation are also demonstrated. With the increase of the accumulated fluence, the CTR is degrading linearly with neutron fluence. The radiation hardening of optocouplers can be improved when the forward current is increased. Other parameters related to CTR degradation of optocouplers are also analyzed.
    Dielectric or plasmonic Mie object at air-liquid interface: The transferred and the traveling momenta of photon
    M R C Mahdy, Hamim Mahmud Rivy, Ziaur Rahman Jony, Nabila Binte Alam, Nabila Masud, Golam Dastegir Al Quaderi, Ibraheem Muhammad Moosa, Chowdhury Mofizur Rahman, M Sohel Rahman
    Chin. Phys. B, 2020, 29 (1):  014211.  DOI: 10.1088/1674-1056/ab5efa
    Abstract ( 129 )   HTML   PDF (3531KB) ( 108 )  
    Considering the inhomogeneous or heterogeneous background, we have demonstrated that if the background and the half-immersed object are both non-absorbing, the transferred photon momentum to the pulled object can be considered as the one of Minkowski exactly at the interface. In contrast, the presence of loss inside matter, either in the half-immersed object or in the background, causes optical pushing of the object. Our analysis suggests that for half-immersed plasmonic or lossy dielectric, the transferred momentum of photon can mathematically be modeled as the type of Minkowski and also of Abraham. However, according to a final critical analysis, the idea of Abraham momentum transfer has been rejected. Hence, an obvious question arises:whence the Abraham momentum? It is demonstrated that though the transferred momentum to a half-immersed Mie object (lossy or lossless) can better be considered as the Minkowski momentum, Lorentz force analysis suggests that the momentum of a photon traveling through the continuous background, however, can be modeled as the type of Abraham. Finally, as an interesting sidewalk, a machine learning based system has been developed to predict the time-averaged force within a very short time avoiding time-consuming full wave simulation.
    Orientation-dependent depolarization of supercontinuum in BaF2 crystal
    Zi-Xi Li(李子熙), Cheng Gong(龚成), Tian-Jiao Shao(邵天骄), Lin-Qiang Hua(华林强), Xue-Bin Bian(卞学滨), Xiao-Jun Liu(柳晓军)
    Chin. Phys. B, 2020, 29 (1):  014212.  DOI: 10.1088/1674-1056/ab5fc7
    Abstract ( 124 )   HTML   PDF (1095KB) ( 106 )  
    We present a systematic investigation of the depolarization properties of a supercontinuum accompanied with femtosecond laser filamentation in barium fluoride (BaF2) crystal. It is found that the depolarization of the supercontinuum depends strongly on the crystal orientations with respect to the incident laser polarization. At most crystal orientations, the depolarization of the supercontinuum rises with the increase of the input laser energies and finally saturates. While at 45°, the depolarization of the supercontinuum is not changed and keeps nearly negligible with the increase of the input laser energies. These peculiar depolarization properties of the supercontinuum can be ascribed to the orientation dependence of the cross-polarized wave (XPW) generation and ionization-induced plasma scattering in the BaF2 crystal.
    Noise properties of multi-combination information in x-ray grating-based phase-contrast imaging
    Wali Faiz, Ji Li(李冀), Kun Gao(高昆), Zhao Wu(吴朝), Yao-Hu Lei(雷耀虎), Jian-Heng Huang(黄建衡), Pei-Ping Zhu(朱佩平)
    Chin. Phys. B, 2020, 29 (1):  014301.  DOI: 10.1088/1674-1056/ab5780
    Abstract ( 122 )   HTML   PDF (864KB) ( 90 )  
    Grating-based x-ray phase contrast imaging has attracted increasing interest in recent decades as multimodal and laboratory source usable method. Specific efforts have been focused on establishing a new extraction method to perform practical applications. In this work, noise properties of multi-combination information of newly established information extraction method, so-called angular signal radiography method, are investigated to provide guidelines for targeted and specific applications. The results show that how multi-combination of images can be used in targeted practical applications to obtain a high-quality image in terms of signal-to-noise ratio. Our conclusions can also hold true for upcoming targeted practical applications such as biomedical imaging, non-destructive imaging, and materials science.
    Micro-crack detection of nonlinear Lamb wave propagation in three-dimensional plates with mixed-frequency excitation
    Wei-Guang Zhu(祝伟光), Yi-Feng Li(李义丰), Li-Qiang Guan(关立强), Xi-Li Wan(万夕里), Hui-Yang Yu(余辉洋), Xiao-Zhou Liu(刘晓宙)
    Chin. Phys. B, 2020, 29 (1):  014302.  DOI: 10.1088/1674-1056/ab5931
    Abstract ( 125 )   HTML   PDF (2114KB) ( 128 )  
    We propose a nonlinear ultrasonic technique by using the mixed-frequency signals excited Lamb waves to conduct micro-crack detection in thin plate structures. Simulation models of three-dimensional (3D) aluminum plates and composite laminates are established by ABAQUS software, where the aluminum plate contains buried crack and composite laminates comprises cohesive element whose thickness is zero to simulate delamination damage. The interactions between the S0 mode Lamb wave and the buried micro-cracks of various dimensions are simulated by using the finite element method. Fourier frequency spectrum analysis is applied to the received time domain signal and fundamental frequency amplitudes, and sum and difference frequencies are extracted and simulated. Simulation results indicate that nonlinear Lamb waves have different sensitivities to various crack sizes. There is a positive correlation among crack length, height, and sum and difference frequency amplitudes for an aluminum plate, with both amplitudes decreasing as crack thickness increased, i.e., nonlinear effect weakens as the micro-crack becomes thicker. The amplitudes of sum and difference frequency are positively correlated with the length and width of the zero-thickness cohesive element in the composite laminates. Furthermore, amplitude ratio change is investigated and it can be used as an effective tool to detect inner defects in thin 3D plates.
    Sound propagation in inhomogeneous waveguides with sound-speed profiles using the multimodal admittance method
    Qi Li(李琪), Juan Liu(刘娟), Wei Guo(郭威)
    Chin. Phys. B, 2020, 29 (1):  014303.  DOI: 10.1088/1674-1056/ab5940
    Abstract ( 119 )   HTML   PDF (1548KB) ( 108 )  
    The multimodal admittance method and its improvement are presented to deal with various aspects in underwater acoustics, mostly for the sound propagation in inhomogeneous waveguides with sound-speed profiles, arbitrary-shaped liquid-like scatterers, and range-dependent environments. In all cases, the propagation problem governed by the Helmholtz equation is transformed into initial value problems of two coupled first-order evolution equations with respect to the modal components of field quantities (sound pressure and its derivative), by projecting the Helmholtz equation on a constructed orthogonal and complete local basis. The admittance matrix, which is the modal representation of Direchlet-to-Neumann operator, is introduced to compute the first-order evolution equations with no numerical instability caused by evanescent modes. The fourth-order Magnus scheme is used for the numerical integration of differential equations in the numerical implementation. The numerical experiments of sound field in underwater inhomogeneous waveguides generated by point sources are performed. Besides, the numerical results computed by simulation software COMSOL Multiphysics are given to validate the correction of the multimodal admittance method. It is shown that the multimodal admittance method is an efficient and stable numerical method to solve the wave propagation problem in inhomogeneous underwater waveguides with sound-speed profiles, liquid-like scatterers, and range-dependent environments. The extension of the method to more complicated waveguides such as horizontally stratified waveguides is available.
    Theoretical estimation of sonochemical yield in bubble cluster in acoustic field
    Zhuang-Zhi Shen(沈壮志)
    Chin. Phys. B, 2020, 29 (1):  014304.  DOI: 10.1088/1674-1056/ab6108
    Abstract ( 118 )   HTML   PDF (784KB) ( 121 )  
    In order to learn more about the physical phenomena occurring in cloud cavitation, the nonlinear dynamics of a spherical cluster of cavitation bubbles and cavitation bubbles in cluster in an acoustic field excited by a square pressure wave are numerically investigated by considering viscosity, surface tension, and the weak compressibility of the liquid. The theoretical prediction of the yield of oxidants produced inside bubbles during the strong collapse stage of cavitation bubbles is also investigated. The effects of acoustic frequency, acoustic pressure amplitude, and the number of bubbles in cluster on bubble temperature and the quantity of oxidants produced inside bubbles are analyzed. The results show that the change of acoustic frequency, acoustic pressure amplitude, and the number of bubbles in cluster have an effect not only on temperature and the quantity of oxidants inside the bubble, but also on the degradation types of pollutants, which provides a guidance in improving the sonochemical degradation of organic pollutants.
    Evaporation of saline colloidal droplet and deposition pattern
    Hong-Hui Sun(孙弘辉), Wei-Bin Li(李伟斌), Wen-Jie Ji(纪文杰), Guo-Liang Dai(戴国亮), Yong Huan(郇勇), Yu-Ren Wang(王育人), Ding Lan(蓝鼎)
    Chin. Phys. B, 2020, 29 (1):  014701.  DOI: 10.1088/1674-1056/ab5782
    Abstract ( 112 )   HTML   PDF (1643KB) ( 110 )  
    The dynamic process of the evaporation and the desiccation of sessile saline colloidal droplets, and their final deposition are investigated. During the evaporation, the movement of the colloidal particles shows a strong dependence on the salt concentration and the droplet shape. The final deposition pattern indicates a weakened coffee-ring effect in this mixed droplet system. The microscopic observation reveals that as evaporation proceeds, the particle motion trail is affected by the salt concentration of the droplet boundary. The Marangoni flow, which is induced by surface tension gradient originating from the local evaporative peripheral salt enrichment, suppresses the compensation flow towards the contact line of the droplet. The inhomogeneous density and concentration field induced by evaporation or crystallization can be the major reason for various micro-flows. At last stage, the distribution and crystallization of NaCl are affected by the colloidal particles during the drying of the residual liquid film.
    Mechanism from particle compaction to fluidization of liquid-solid two-phase flow
    Yue Zhang(张悦), Jinchun Song(宋锦春), Lianxi Ma(马连喜), Liancun Zheng(郑连存), Minghe Liu(刘明贺)
    Chin. Phys. B, 2020, 29 (1):  014702.  DOI: 10.1088/1674-1056/ab5789
    Abstract ( 102 )   HTML   PDF (1479KB) ( 75 )  
    A new model of particle yield stress including cohesive strength is proposed, which considers the friction and cohesive strength between particles. A calculation method for the fluidization process of liquid-solid two-phase flow in compact packing state is given, and the simulation and experimental studies of fluidization process are carried out by taking the sand-water two-phase flow in the jet dredging system as an example, and the calculation method is verified.
    Acoustic characteristics of pulse detonation engine sound propagating in enclosed space
    Yang Kang(康杨), Ning Li(李宁), Chun-Sheng Weng(翁春生), Xiao-Long Huang(黄孝龙)
    Chin. Phys. B, 2020, 29 (1):  014703.  DOI: 10.1088/1674-1056/ab5b88
    Abstract ( 101 )   HTML   PDF (2810KB) ( 126 )  
    Acoustic characteristics of pulse detonation engine (PDE) sound propagating in enclosed space are numerically and experimentally investigated. The finite element software LS-DYNA is utilized to numerically simulate the PDE sound propagating in enclosed space. Acoustic measurement systems are established for testing the PDE sound in enclosed space, and the time-frequency characteristics of PDE sound in enclosed space are reported in detail. The experimental results show that the sound waveform of PDE sound in enclosed space are quite different from those in open space, and the reflection and superposition of PDE sound on the walls of enclosed space results in the sound pressure oscillating obviously. It is found that the peak sound pressure level (PSPL) and overall sound pressure level (OASPL) of PDE sound in enclosed space are higher than those in open space and their difference increases with the rise of propagation distance. The results of the duration of PDE sound indicate that the A duration of PDE sound in enclosed space is higher than that in open space except at measuring points located at 2-m and 5-m while the B duration is higher at each of all measuring points. Results show that the enclosed space has a great influence on the acoustic characteristic of PDE sound. This research is helpful in performing PDE experiments in enclosed laboratories to prevent the PDE sound from affecting the safety of laboratory environment, equipment, and staffs.
    Beryllium carbide as diffusion barrier against Cu: First-principles study
    Hua-Liang Cao(曹华亮), Xin-Lu Cheng(程新路), Hong Zhang(张红)
    Chin. Phys. B, 2020, 29 (1):  016601.  DOI: 10.1088/1674-1056/ab593e
    Abstract ( 129 )   HTML   PDF (4920KB) ( 154 )  
    Beryllium carbide is used in inertial confinement fusion (ICF) capsule ablation material due to its low atomic number, low opacity, and high melting point properties. We used the method of climbing image nudged elastic band (CINEB) to calculate the diffusion barrier of copper atom in the crystal of beryllium and beryllium carbide. The diffusion barrier of copper atom in crystal beryllium is only 0.79 eV, and the barrier in beryllium carbide is larger than 2.85 eV. The three structures of beryllium carbide:anti-fluorite Be2C, Be2C-I, and Be2C-III have a good blocking effect to the diffusion of copper atom. Among them, the Be2C-III structure has the highest diffusion barrier of 6.09 eV. Our research can provide useful help for studying Cu diffusion barrier materials.
    Sodium decorated net-Y nanosheet for hydrogen storage and adsorption mechanism: A first-principles study
    Yunlei Wang(王云蕾), Yuhong Chen(陈玉红), Yunhui Wang(王允辉)
    Chin. Phys. B, 2020, 29 (1):  016801.  DOI: 10.1088/1674-1056/ab5785
    Abstract ( 137 )   HTML   PDF (1906KB) ( 89 )  
    Using first-principles calculations based on density functional theory (DFT), we investigate the potential hydrogen storage capacity of the Na-decorated net-Y single layer nanosheet. For double-side Na decoration, the average binding energy is 1.54 eV, which is much larger than the cohesive energy of 1.13 eV for bulk Na. A maximum of four H2 molecules can be adsorbed around each Na with average adsorption energies of 0.25-0.32 eV/H2. Also, H2 storage gravimetric of 8.85 wt% is obtained, and this meets the U.S. Department of Energy (DOE) ultimate target. These results are instrumental in seeking a promising hydrogen energy carrier.
    First-principles study of high performance lithium/sodium storage of Ti3C2T2 nanosheets as electrode materials
    Li-Na Bai(白丽娜), Ling-Ying Kong(孔令莹), Jing Wen(温静), Ning Ma(马宁), Hong Gao(高红), Xi-Tian Zhang(张喜田)
    Chin. Phys. B, 2020, 29 (1):  016802.  DOI: 10.1088/1674-1056/ab592e
    Abstract ( 131 )   HTML   PDF (4563KB) ( 115 )  
    Ti3C2Tx nanosheet, the first synthesized MXene with high capacity performance and charge/discharge rate, has attracted increasingly attention in renewable energy storage applications. By performing systematic density functional theory calculations, the theoretical capacity of the intrinsic structure of single- and multi-layered Ti3C2T2 (T=F or O) corresponding to M (M=Li and Na) atoms are investigated. Theoretical volumetric capacity and gravimetric capacity are obtained, which are related to the stacking degree. The optimal ratios of capacity to structure are determined under different stacking degrees for understanding the influence of surface functional groups on energy storage performance. Its performance can be tuned by performing surface modification and increasing the interlayer distance. In addition, the reason for theoretical capacity differences of M atoms is analyzed, which is attributed to difference in interaction between the M-ions and substrate and the difference in electrostatic exclusion between adsorbed M-ions. These results provide an insight into the understanding of the method of efficiently increasing the energy storage performance, which will be useful for designing and using high performance electrode materials.
    Giant topological Hall effect of ferromagnetic kagome metal Fe3Sn2 Hot!
    Qi Wang(王琦), Qiangwei Yin(殷蔷薇), Hechang Lei(雷和畅)
    Chin. Phys. B, 2020, 29 (1):  017101.  DOI: 10.1088/1674-1056/ab5fbc
    Abstract ( 307 )   HTML   PDF (671KB) ( 362 )  
    We present the experiment observation of a giant topological Hall effect (THE) in a frustrated kagome bilayer magnet Fe3Sn2. The negative topologically Hall resistivity appears when the field is below 1.3 T and it increases with increasing temperature up to 300 K. Its maximum absolute value reaches ~2.01 μΩ·cm at 300 K and 0.76 T. The origins of the observed giant THE can be attributed to the coexistence of the field-induced skyrmion state and the non-collinear spin configuration, possibly related to the magnetic frustration interaction in Fe3Sn2.
    Improvement of radiative recombination rate in deep ultraviolet laser diodes with step-like quantum barrier and aluminum-content graded electron blocking layer
    Yi-Fu Wang(王一夫), Mussaab I Niass, Fang Wang(王芳), Yu-Huai Liu(刘玉怀)
    Chin. Phys. B, 2020, 29 (1):  017301.  DOI: 10.1088/1674-1056/ab592c
    Abstract ( 165 )   HTML   PDF (723KB) ( 95 )  
    The design of the active region structures, including the modifications of structures of the quantum barrier (QB) and electron blocking layer (EBL), in the deep ultraviolet (DUV) AlGaN laser diode (LD) is investigated numerically with the Crosslight software. The analyses focus on electron and hole injection efficiency, electron leakage, hole diffusion, and radiative recombination rate. Compared with the reference QB structure, the step-like QB structure provides high radiative recombination and maximum output power. Subsequently, a comparative study is conducted on the performance characteristics with four different EBLs. For the EBL with different Al mole fraction layers, the higher Al-content AlGaN EBL layer is located closely to the active region, leading the electron current leakage to lower, the carrier injection efficiency to increase, and the radiative recombination rate to improve.
    Tetraalkyl-substituted zinc phthalocyanines used as anode buffer layers for organic light-emitting diodes
    Qian Chen(陈潜), Songhe Yang(杨松鹤), Lei Dong(董磊), Siyuan Cai(蔡思源), Jiaju Xu(许家驹), Zongxiang Xu(许宗祥)
    Chin. Phys. B, 2020, 29 (1):  017302.  DOI: 10.1088/1674-1056/ab5933
    Abstract ( 100 )   HTML   PDF (2018KB) ( 72 )  
    Two soluble tetraalkyl-substituted zinc phthalocyanines (ZnPcs) for use as anode buffer layer materials in tris(8-hydroxyquinoline)aluminum (Alq3)-based organic light-emitting diodes (OLEDs) are presented in this work. The hole-blocking properties of these ZnPc layers slowed the hole injection process into the Alq3 emissive layer greatly and thus reduced the production of unstable cationic Alq3 (Alq3+) species. This led to the enhanced brightness and efficiency when compared with the corresponding properties of OLEDs based on the popular poly-(3, 4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer. Furthermore, because of the high thermal and chemical stabilities of these ZnPcs, a nonaqueous film fabrication process was realized together with improved charge balance in the OLEDs and enhanced OLED lifetimes.
    Tunneling magnetoresistance in ferromagnet/organic-ferromagnet/metal junctions
    Yan-Qi Li(李彦琪), Hong-Jun Kan(阚洪君), Yuan-Yuan Miao(苗圆圆), Lei Yang(杨磊), Shuai Qiu(邱帅), Guang-Ping Zhang(张广平), Jun-Feng Ren(任俊峰), Chuan-Kui Wang(王传奎), Gui-Chao Hu(胡贵超)
    Chin. Phys. B, 2020, 29 (1):  017303.  DOI: 10.1088/1674-1056/ab5d02
    Abstract ( 164 )   HTML   PDF (1378KB) ( 141 )  
    Spin-dependent transport in ferromagnet/organic-ferromagnet/metal junctions is investigated theoretically. The results reveal a large tunneling magnetoresistance up to 3230% by controlling the relative magnetization orientation between the ferromagnet and the central organic ferromagnet. The mechanism is explained by distinct efficient spin-resolved tunneling states in the ferromagnet between the parallel and antiparallel spin configurations. The key role of the organic ferromagnet in generating the large magnetoresistance is explored, where the spin selection effect is found to enlarge the difference of the tunneling states between the parallel and antiparallel configurations by comparing with the conventional organic spin valves. The effects of intrinsic interactions in the organic ferromagnet including electron-lattice interaction and spin coupling with radicals on the magnetoresistance are discussed. This work demonstrates a promising potential of organic ferromagnets in the design of high-performance organic spin valves.
    Surface Majorana flat bands in j=3/2 superconductors with singlet-quintet mixing Hot!
    Jiabin Yu(于家斌), Chao-Xing Liu(刘朝星)
    Chin. Phys. B, 2020, 29 (1):  017402.  DOI: 10.1088/1674-1056/ab5b89
    Abstract ( 202 )   HTML   PDF (1444KB) ( 136 )  
    Recent experiments[Science Advances 4 eaao4513 (2018)] have revealed the evidence of nodal-line superconductivity in half-Heusler superconductors, e.g., YPtBi. Theories have suggested the topological nature of such nodal-line superconductivity and proposed the existence of surface Majorana flat bands on the (111) surface of half-Heusler superconductors. Due to the divergent density of states of the surface Majorana flat bands, the surface order parameter and the surface impurity play essential roles in determining the surface properties. We study the effect of the surface order parameter and the surface impurity on the surface Majorana flat bands of half-Heusler superconductors based on the Luttinger model. To be specific, we consider the topological nodal-line superconducting phase induced by the singlet-quintet pairing mixing, classify all the possible translationally invariant order parameters for the surface states according to irreducible representations of C3v point group, and demonstrate that any energetically favorable order parameter needs to break the time-reversal symmetry. We further discuss the energy splitting in the energy spectrum of surface Majorana flat bands induced by different order parameters and non-magnetic or magnetic impurities. We propose that the splitting in the energy spectrum can serve as the fingerprint of the pairing symmetry and mean-field order parameters. Our theoretical prediction can be examined in the future scanning tunneling microscopy experiments.
    Non-parabolic effect for femtosecond laser-induced ultrafast electro-absorption in solids
    Li-Bo Liu(刘利博), Hong-Xiang Deng(邓洪祥), Xiao-Tao Zu(祖小涛), Xiao-Dong Yuan(袁晓东), Wan-Guo Zheng(郑万国)
    Chin. Phys. B, 2020, 29 (1):  017801.  DOI: 10.1088/1674-1056/ab577c
    Abstract ( 160 )   HTML   PDF (542KB) ( 84 )  
    A theoretical study for femtosecond laser-induced ultrafast electro-absorption of bulk solids is presented. Our numerical results show that, in the case of low intensity of the pump laser where the interaction between the pump laser and solids is in the multi-photon regime, the energy band of solids can be approximately taken as a parabolic band and electro-absorption spectrums from the parabolic band and real band are nearly the same. While, in the case of high intensity where the interaction is in the tunneling regime, spectrums from the parabolic band and real band are quite different. The physical mechanism for the difference in the tunneling regime is found. We find that the non-parabolic parts of the real energy band and Bragger scattering of electrons near the first Brillouin zone boundaries, which are neglected in previous studies, strongly influence the electro-absorption spectrum in the tunneling regime. These two physical processes cause the difference of spectrums. Our theoretical results are in accordance with the experiment result.
    Thickness-dependent excitonic properties of atomically thin 2H-MoTe2
    Jin-Huan Li(李金焕), Dan Bing(邴单), Zhang-Ting Wu(吴章婷), Guo-Qing Wu(吴国庆), Jing Bai(白静), Ru-Xia Du(杜如霞), Zheng-Qing Qi(祁正青)
    Chin. Phys. B, 2020, 29 (1):  017802.  DOI: 10.1088/1674-1056/ab5a3a
    Abstract ( 160 )   HTML   PDF (1275KB) ( 234 )  
    Two-dimensional (2D) 2H-MoTe2 is a promising semiconductor because of its small bandgap, strong absorption, and low thermal conductivity. In this paper, we systematically study the optical and excitonic properties of atomically thin 2H-MoTe2 (1-5 layers). Due to the fact that the optical contrast and Raman spectra of 2H-MoTe2 with different thicknesses exhibit distinctly different behaviors, we establish a quantitative method by using optical images and Raman spectra to directly identify the layers of 2H-MoTe2 thin films. Besides, excitonic states and binding energy in monolayer/bilayer 2H-MoTe2 are measured by temperature-dependent photoluminescence (PL) spectroscopy. At temperature T=3.3 K, we can observe an exciton emission at ~1.19 eV and trion emission at ~1.16 eV for monolayer 2H-MoTe2. While at room temperature, the exciton emission and trion emission both disappear for their small binding energy. We determine the exciton binding energy to be 185 meV (179 meV), trion binding energy to be 20 meV (18 meV) for the monolayer (bilayer) 2H-MoTe2. The thoroughly studies of the excitonic states in atomically thin 2H-MoTe2 will provide guidance for future practical applications.
    Growth characteristics of type IIa large single crystal diamond with Ti/Cu as nitrogen getter in FeNi-C system
    Ming-Ming Guo(郭明明), Shang-Sheng Li(李尚升), Mei-Hua Hu(胡美华), Tai-Chao Su(宿太超), Jun-Zuo Wang(王君卓), Guang-Jin Gao(高广进), Yue You(尤悦), Yuan Nie(聂媛)
    Chin. Phys. B, 2020, 29 (1):  018101.  DOI: 10.1088/1674-1056/ab592f
    Abstract ( 148 )   HTML   PDF (1712KB) ( 102 )  
    High-quality type I!Ia large diamond crystals are synthesized with Ti/Cu as nitrogen getter doped in an FeNi-C system at temperature ranging from 1230 ℃ to 1380 ℃ and at pressure 5.3-5.9 GPa by temperature gradient method. Different ratios of Ti/Cu are added to the FeNi-C system to investigate the best ratio for high-quality type I!Ia diamond. Then, the different content of nitrogen getter Ti/Cu (Ti:Cu=4:3) is added to this synthesis system to explore the effect on diamond growth. The macro and micro morphologies of synthesized diamonds with Ti/Cu added, whose nitrogen concentration is determined by Fourier transform infrared (FTIR), are analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. It is found that the inclusions in the obtained crystals are minimal when the Ti/Cu ratio is 4:3. Furthermore, the temperature interval for diamond growth becomes narrower when using Ti as the nitrogen getter. Moreover, the lower edge of the synthesis temperature of type IIa diamond is 25 ℃ higher than that of type Ib diamond. With the increase of the content of Ti/Cu (Ti:Cu=4:3), the color of the synthesized crystals changes from yellow and light yellow to colorless. When the Ti/Cu content is 1.7 wt%, the nitrogen concentration of the crystal is less than 1 ppm. The SEM results show that the synthesized crystals are mainly composed by (111) and (100) surfaces, including (311) surface, when the nitrogen getter is added into the synthesis system. At the same time, there are triangular pits and dendritic growth stripes on the crystal surface. This work will contribute to the further research and development of high-quality type I!Ia diamond.
    Room temperature non-balanced electric bridge ethanol gas sensor based on a single ZnO microwire
    Yun-Zheng Li(李昀铮), Qiu-Ju Feng(冯秋菊), Bo Shi(石博), Chong Gao(高冲), De-Yu Wang(王德煜), Hong-Wei Liang(梁红伟)
    Chin. Phys. B, 2020, 29 (1):  018102.  DOI: 10.1088/1674-1056/ab593f
    Abstract ( 162 )   HTML   PDF (1120KB) ( 88 )  
    In this paper, ultra-long and large-scaled ZnO microwire arrays are grown by the chemical vapor deposition method, and a single ZnO microwire-based non-balanced electric bridge ethanol gas sensor is fabricated. The experimental results show that the gas sensor has good repeatability, high response rate, short response, and recovery time at room temperature (25 ℃). The response rate of the gas sensor exposed to 90-ppm ethanol is about 93%, with a response time and recovery time are 0.3 s and 0.7 s respectively. As a contrast, the traditional resistive gas sensor of a single ZnO microwire shows very small gas response rate. Therefore, ethanol gas sensor based on non-balanced electric bridge can obviously enhance gas sensing characteristics, which provides a feasible method of developing the high performance ZnO-based gas sensor.
    Influences of grain size and microstructure on optical properties of microcrystalline diamond films
    Jia-Le Wang(王家乐), Cheng-Ke Chen(陈成克), Xiao Li(李晓), Mei-Yan Jiang(蒋梅燕), Xiao-Jun Hu(胡晓君)
    Chin. Phys. B, 2020, 29 (1):  018103.  DOI: 10.1088/1674-1056/ab593d
    Abstract ( 110 )   HTML   PDF (1870KB) ( 99 )  
    Microcrystalline diamond (MCD) films with different grain sizes ranging from 160 nm to 2200 nm are prepared by using a hot filament chemical vapor deposition (HFCVD) system, and the influences of grain size and structural features on optical properties are investigated. The results show that the film with grain size in a range of 160 nm-310 nm exhibits a higher refractive index in a range of (2.77-2.92). With grain size increasing to 620±300 nm, the refractive index shows a value between 2.39 and 2.47, approaching to that of natural diamond (2.37-2.55), and a lower extinction coefficient value between 0.08 and 0.77. When the grain size increases to 2200 nm, the value of refractive index increases to a value between 2.66 and 2.81, and the extinction coefficient increases to a value in a range of 0.22-1.28. Visible Raman spectroscopy measurements show that all samples have distinct diamond peaks located in a range of 1331 cm-1-1333 cm-1, the content of diamond phase increases gradually as grain size increases, and the amount of trans-polyacetylene (TPA) content decreases. Meanwhile, the sp2 carbon clusters content and its full-width-at-half-maximum (FWHM) value are significantly reduced in MCD film with a grain size of 620 nm, which is beneficial to the improvement of the optical properties of the films.
    Optical and electrical properties of InGaZnON thin films
    Jian Ke Yao(姚建可), Fan Ye(叶凡), Ping Fan(范平)
    Chin. Phys. B, 2020, 29 (1):  018105.  DOI: 10.1088/1674-1056/ab5fc1
    Abstract ( 138 )   HTML   PDF (1410KB) ( 105 )  
    The substrate temperature (Ts) and N2 partial pressure (PN2) dependent optical and electrical properties of sputtered InGaZnON thin films are studied. With the increased Ts and PN2, the thin film becomes more crystallized and nitrified. The Hall mobility, free carrier concentration (Ne), and electrical conductivity increase with the lowered interfacial potential barrier during crystal growing. The photoluminescence (PL) intensity decreases with the increased Ne. The band gap (Eg) narrows and the linear refractive index (n1) increases with the increasing concentration of N in the thin films. The Stokes shift between the PL peak and absorption edge decreases with Eg. The n1, dispersion energy, average oscillator wavelength, and oscillator length strength all increase with n1. The single oscillator energy decreases with n1. The nonlinear refractive index and third order optical susceptibility increase with n1. The Seebeck coefficient, electron effective mass, mean free path, scattering time, and plasma energy are all Ne dependent.
    Infrared light-emitting diodes based on colloidal PbSe/PbS core/shell nanocrystals
    Byung-Ryool Hyun, Mikita Marus, Huaying Zhong(钟华英), Depeng Li(李德鹏), Haochen Liu(刘皓宸), Yue Xie(谢阅), Weon-kyu Koh, Bing Xu(徐冰), Yanjun Liu(刘言军), Xiao Wei Sun(孙小卫)
    Chin. Phys. B, 2020, 29 (1):  018503.  DOI: 10.1088/1674-1056/ab5fb7
    Abstract ( 140 )   HTML   PDF (1218KB) ( 132 )  
    Colloidal PbSe nanocrystals (NCs) have gained considerable attention due to their efficient carrier multiplication and emissions across near-infrared and short-wavelength infrared spectral ranges. However, the fast degradation of colloidal PbSe NCs in ambient conditions hampers their widespread applications in infrared optoelectronics. It is well-known that the inorganic thick-shell over core improves the stability of NCs. Here, we present the synthesis of PbSe/PbS core/shell NCs showing wide spectral tunability, in which the molar ratio of lead (Pb) and sulfur (S) precursors, and the concentration of sulfur and PbSe NCs in solvent have a significant effect on the efficient PbS shell growth. The infrared light-emitting diodes (IR-LEDs) fabricated with the PbSe/PbS core/shell NCs exhibit an external quantum efficiency (EQE) of 1.3% at 1280 nm. The ligand exchange to optimize the distance between NCs and chloride treatment are important processes for achieving high performance on PbSe/PbS NC-LEDs. Our results provide evidence for the promising potential of PbSe/PbS NCs over the wide range of infrared optoelectronic applications.
    Phase transition of DNA compaction in confined space: Effects of macromolecular crowding are dominant
    Erkun Chen(陈尔坤), Yangtao Fan(范洋涛), Guangju Zhao(赵光菊), Zongliang Mao(毛宗良), Haiping Zhou(周海平), Yanhui Liu(刘艳辉)
    Chin. Phys. B, 2020, 29 (1):  018701.  DOI: 10.1088/1674-1056/ab5941
    Abstract ( 142 )   HTML   PDF (1197KB) ( 97 )  
    With a view of detecting the effects of macromolecular crowding on the phase transition of DNA compaction confined in spherical space, Monte Carlo simulations of DNA compaction in free space, in confined spherical space without crowders and in confined spherical space with crowders were performed separately. The simulation results indicate that macromolecular crowding effects on DNA compaction are dominant over the roles of multivalent counterions. In addition, effects of temperature on the phase transition of DNA compaction have been identified in confined spherical space with different radii. In confined spherical space without crowders, the temperature corresponding to phase transition depends on the radius of the confined spherical space linearly. In contrast, with the addition of crowders to the confined spherical space, effects of temperature on the phase transition of DNA compaction become insignificant, whereas the phase transition at different temperatures strongly depends on the size of crowder, and the critical volume fraction of crowders pertains to the diameter of crowder linearly.
    Major impact of queue-rule choice on the performance of dynamic networks with limited buffer size
    Xiang Ling(凌翔), Xiao-Kun Wang(王晓坤), Jun-Jie Chen(陈俊杰), Dong Liu(刘冬), Kong-Jin Zhu(朱孔金), Ning Guo(郭宁)
    Chin. Phys. B, 2020, 29 (1):  018901.  DOI: 10.1088/1674-1056/ab5935
    Abstract ( 130 )   HTML   PDF (526KB) ( 73 )  
    We investigate the similarities and differences among three queue rules, the first-in-first-out (FIFO) rule, last-in-first-out (LIFO) rule and random-in-random-out (RIRO) rule, on dynamical networks with limited buffer size. In our network model, nodes move at each time step. Packets are transmitted by an adaptive routing strategy, combining Euclidean distance and node load by a tunable parameter. Because of this routing strategy, at the initial stage of increasing buffer size, the network density will increase, and the packet loss rate will decrease. Packet loss and traffic congestion occur by these three rules, but nodes keep unblocked and lose no packet in a larger buffer size range on the RIRO rule networks. If packets are lost and traffic congestion occurs, different dynamic characteristics are shown by these three queue rules. Moreover, a phenomenon similar to Braess' paradox is also found by the LIFO rule and the RIRO rule.
ISSN 1674-1056   CN 11-5639/O4
, Vol. 29, No. 1

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