Chin. Phys. B

Rational solutions and interaction solutions for (2 + 1)-dimensional nonlocal Schrödinger equation Suggested by editors

Mi Chen(陈觅) and Zhen Wang(王振)

Chin. Phys. B, 2020, 29 (12): 120201. DOI: 10.1088/1674-1056/abc165

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A chain of novel higher order rational solutions with some parameters and interaction solutions of a (2+1)-dimensional reverse space-time nonlocal Schrödinger (NLS) equation was derived by a generalized Darboux transformation (DT) which is derived by Taylor expansion and determinants. We obtained a series of higher-order rational solutions by one spectral parameter and we could get the periodic wave solution and three kinds of interaction solutions, singular breather and periodic wave interaction solution, singular breather and traveling wave interaction solution, bimodal breather and periodic wave interaction solution by two spectral parameters. We found a general formula for these solutions in the form of determinants. We also analyzed the complex wave structures of the dynamic behaviors and the effects of special parameters and presented exact solutions for the (2+1)-dimensional reverse space-time nonlocal NLS equation.

Double differential cross sections for ionization of H by 75 keV proton impact: Assessing the role of correlated wave functions Suggested by editors

Jungang Fan(范军刚), Xiangyang Miao(苗向阳), and Xiangfu Jia(贾祥福)

Chin. Phys. B, 2020, 29 (12): 120301. DOI: 10.1088/1674-1056/abb7f8

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The effect of final-state dynamic correlation is investigated for ionization of atomic hydrogen by 75-keV proton impact by analyzing double differential cross sections. The final state is represented by a continuum correlated wave (CCW-PT) function which accounts for the interaction between the projectile and the target nucleus (PT interaction). The correlated final state is nonseparable solutions of the wave equation combining the dynamics of the electron motion relative to the target and projectile, satisfying the Redmond's asymptotic conditions corresponding to long range interactions. The transition matrix is evaluated using the CCW-PT function and the undistorted initial state. Both the correlation effects and the PT interaction are analyzed by the present calculations. The convergence of the continuous correlated final state is examined carefully. Our results are compared with the absolute experimental data measured by Laforge et al. [Phys. Rev. Lett. 103, 053201 (2009)] and Schulz et al. [Phys. Rev. A 81, 052705 (2010)], as well as other theoretical models (especially the results of the latest non perturbation theory). We have shown that the dynamic correlation plays an important role in the ionization of atomic hydrogen by proton impact. While overall agreement between theory and the experimental data is encouraging, detailed agreement is still lacking. However, such an analysis is meaningful because it provides valuable information about the dynamical correlation and PT interaction in the CCW-PT theoretical model.

Chaotic dynamics of complex trajectory and its quantum signature

Wen-Lei Zhao(赵文垒), Pengkai Gong(巩膨恺), Jiaozi Wang(王骄子), and Qian Wang(王骞)

Chin. Phys. B, 2020, 29 (12): 120302. DOI: 10.1088/1674-1056/abc0dc

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We investigate both the quantum and classical dynamics of a non-Hermitian system via a kicked rotor model with $\mathcalPT$ symmetry. For the quantum dynamics, both the mean momentum and mean square of momentum exhibit the staircase growth with time when the system parameter is in the neighborhood of the $\mathcalPT$ symmetry breaking point. If the system parameter is much larger than the $\mathcalPT$ symmetry breaking point, the accelerator mode results in the directed spreading of the wavepackets as well as the ballistic diffusion in momentum space. For the classical dynamics, the non-Hermitian kicking potential leads to the exponentially-fast increase of classical complex trajectories. As a consequence, the imaginary part of the trajectories exponentially diffuses with time, while the real part exhibits the normal diffusion. Our analytical prediction of the exponential diffusion of imaginary momentum and its breakdown time is in good agreement with numerical results. The quantum signature of the chaotic diffusion of the complex trajectories is reflected by the dynamics of the out-of-time-order correlators (OTOC). In the semiclassical regime, the rate of the exponential increase of the OTOC is equal to that of the exponential diffusion of the complex trajectories.

Optimal parameter estimation of open quantum systems

Yinghua Ji(嵇英华), Qiang Ke(柯强), and Juju Hu(胡菊菊)

Chin. Phys. B, 2020, 29 (12): 120303. DOI: 10.1088/1674-1056/abc0d1

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In quantum information technologies, quantum weak measurement is beneficial for protecting coherence of systems. In order to further improve the protection effect of quantum weak measurement on coherence, we propose an optimization scheme of quantum Fisher information (QFI) protection in an open quantum system by combing no-knowledge quantum feedback control with quantum weak measurement. On the basis of solving the dynamic equations of a stochastic two-level quantum system under feedback control, we compare the effects of different feedback Hamiltonians on QFI and find that via no-knowledge quantum feedback, the observation operator σ _x (or σ _x and σ _z ) can protect QFI for a long time. Namely, no-knowledge quantum feedback can improve the estimation precision of feedback coefficient as well as that of detection coefficient.

Unconventional photon blockade in a three-mode system with double second-order nonlinear coupling

Hong-Yu Lin(林宏宇), Hui Yang(杨慧), and Zhi-Hai Yao(姚治海)

Chin. Phys. B, 2020, 29 (12): 120304. DOI: 10.1088/1674-1056/abab82

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The unconventional photon blockade (UPB) for low-frequency mode is investigated in a three-mode system with double second-order nonlinearity. By analyzing the Hamiltonian of the system, the optimal analytic condition of UPB in low-frequency mode is obtained. The numerical results are calculated by solving the master equation in a truncated Fock space, which agrees well with the analytic conditions. Through the numerical analysis of the system, it is found that the weak driving strength is favorable for the system to realize the UPB effect, and the system is insensitive to the changes of attenuation rate and environmental temperature. The comparison with the two-mode system and another similar three-mode system shows that, under similar system parameters, the UPB effect of this double two-order nonlinear system is more obvious.

Peierls-phase-induced topological semimetals in an optical lattice: Moving of Dirac points, anisotropy of Dirac cones, and hidden symmetry protection ^Hot!

Jing-Min Hou(侯净敏)

Chin. Phys. B, 2020, 29 (12): 120305. DOI: 10.1088/1674-1056/abc0de

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We propose a square optical lattice in which some of neighbor hoppings have a Peierls phase. The Peierls phase makes the lattice have a special band structure and induces the existence of Dirac points in the Brillouin zone, which means that topological semimetals exist in the system. The Dirac points move with the change of the Peierls phase and the Dirac cones are anisotropic for some vales of the Peierls phase. The lattice has a novel hidden symmetry, which is a composite antiunitary symmetry composed of a translation operation, a sublattice exchange, a complex conjugation, and a local U(1) gauge transformation. We prove that the Dirac points are protected by the hidden symmetry and perfectly explain the moving of Dirac points with the change of the Peierls phase based on the hidden symmetry protection.

A note on the definition of gravitational energy for quadratic curvature gravity via topological regularization

Meng-Liang Wang(王梦亮) and Jun-Jin Peng(彭俊金)

Chin. Phys. B, 2020, 29 (12): 120401. DOI: 10.1088/1674-1056/abb3e0

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Within the framework of four-dimensional quadratic curvature gravities in the appearance of a negative cosmological constant, a definition for the gravitational energy of solutions with anti-de Sitter (AdS) asymptotics was put forward by Giribet et al. [Phys. Rev. D 98 044046 (2018)]. This was achieved by adding proper topological invariant terms to the gravity action to render the variation problem well-posed. We prove that the definition via the procedure of topological regularization can be covered by our previous work [Int. J. Mod. Phys. A 35 2050102 (2020)] in four dimensions. Motivated by this, we further generalize the results to generic diffeomorphism invariant theories of gravity in arbitrary even dimensions.

Nonlinear resonances phenomena in a modified Josephson junction model

Pernel Nguenang, Sandrine Takam Mabekou, Patrick Louodop, Arthur Tsamouo Tsokeng, and Martin Tchoffo

Chin. Phys. B, 2020, 29 (12): 120501. DOI: 10.1088/1674-1056/aba9cd

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In this paper, the equivalent circuit of the non-autonomous Josephson junction (JJ) is presented and the effect of the proper frequency on the phase φ is studied. We also study nonlinear resonance phenomena in the oscillations of a modified Josephson junction (MJJ). These oscillations are probed through a system of nonlinear differential equations and the multiple time scale method is employed to investigate all different types of resonance that occur. The results of primary, superharmonic and subharmonic resonances are obtained analytically. We show that the system exhibits hardening and softening behaviors, as well as hysteresis and amplitude hopping phenomena in primary and superharmonic resonances, and only the hysteresis phenomenon in subharmonic resonance. In addition, the stabilities and the steady state solutions in each type of resonances are kindly evaluated. The number of equilibrium points that evolve with time and their stabilities are also studied. Finally, the equations of motion are numerically integrated to check the correctness of analytical calculations. We further show that the dynamics of the MJJ is strongly influenced by its parameters.

Localized characteristics of lump and interaction solutions to two extended Jimbo-Miwa equations

Yu-Hang Yin(尹宇航), Si-Jia Chen(陈思佳), and Xing Lü(吕兴)

Chin. Phys. B, 2020, 29 (12): 120502. DOI: 10.1088/1674-1056/aba9c4

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We focus on the localized characteristics of lump and interaction solutions to two extended Jimbo-Miwa equations. Based on the Hirota bilinear method and the test function method, we construct the exact solutions to the extended equations including lump solutions, lump-kink solutions, and two other types of interaction solutions, by solving the under-determined nonlinear system of algebraic equations for associated parameters. Finally, analysis and graphical simulation are presented to show the dynamical characteristics of our solutions and the interaction behaviors are revealed.

Energy relaxation in disordered lattice φ⁴ system: The combined effects of disorder and nonlinearity

Jianjin Wang(汪剑津), Yong Zhang(张勇), and Daxing Xiong(熊大兴)

Chin. Phys. B, 2020, 29 (12): 120503. DOI: 10.1088/1674-1056/abc15b

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We address the issue of how disorder together with nonlinearity affect energy relaxation in the lattice φ⁴ system. The absence of nonlinearity leads such a model to only supporting fully localized Anderson modes whose energies will not relax. However, through exploring the time decay behavior of each Anderson mode's energy-energy correlation, we find that adding nonlinearity, three distinct relaxation details can occur. (i) A small amount of nonlinearity causes a rapid exponential decay of the correlation for all modes. (ii) In the intermediate value of nonlinearity, this exponential decay will turn to power-law with a large scaling exponent close to -1. (iii) Finally, all Anderson modes' energies decay in a power-law manner but with a quite small exponent, indicating a slow long-time tail decay. Obviously, the last two relaxation details support a new localization mechanism. As an application, we show that these are relevant to the nonmonotonous nonlinearity dependence of thermal conductivity. Our results thus provide new information for understanding the combined effects of disorder and nonlinearity on energy relaxation.

The landscape and flux of a minimum network motif, Wu Xing Suggested by editors

Kun Zhang(张坤), Ashley Xia(夏月), and Jin Wang(汪劲)

Chin. Phys. B, 2020, 29 (12): 120504. DOI: 10.1088/1674-1056/abc2bf

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Wu-Xing theory is an ancient philosophy that serves as a guiding principle in the traditional Chinese medicine (TCM). It has been used to explain the unbalance among the TCM organ systems in disease states and provide treatment philosophy qualitatively. Until now, it is still a challenge to explore the Wu-Xing theory beyond its philosophical nature. In this study, we established a quantitative framework using the landscape and flux theory to characterize the nature of the Wu-Xing theory from a perspective of a minimal network motif and leave certain specific functional aspects of Wu-Xing theory for future exploration. We uncovered the irregular ring shape of projection landscape for the Wu-Xing network with several local basins and barriers. We found that the dynamics of the self-organized Wu-Xing system was determined by the underlying negative landscape gradient force and the nonequilibrium rotational flux. While the shape of the Wu-Xing landscape determines the stabilities of the states, the rotational flux guarantees the persistent periodic oscillation and the stability of the flow. This provides a physical and quantitative basis for Yin-Yang duality of the driving forces for determining the dynamics and behaviors of the living systems. Applying landscape and flux analysis, we can identify the key parameter for the dynamics/function of Wu-Xing network. These findings allow us to have a deeper understanding of the scientific merits of the ancient Wu-Xing theory from the network motif perspective.

Nonequilibrium reservoir engineering of a biased coherent conductor for hybrid energy transport in nanojunctions

"Bing-Zhong Hu(胡柄中), Lei-Lei Nian(年磊磊), and Jing-Tao Lü(吕京涛)

Chin. Phys. B, 2020, 29 (12): 120505. DOI: 10.1088/1674-1056/abb3ee

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We show that a current-carrying coherent electron conductor can be treated as an effective bosonic energy reservoir involving different types of electron-hole pair excitations. For weak electron-boson coupling, hybrid energy transport between nonequilibrium electrons and bosons can be described by a Landauer-like formula. This allows for unified account of a variety of heat transport problems in hybrid electron-boson systems. As applications, we study the non-reciprocal heat transport between electrons and bosons, thermoelectric current from a cold-spot, and electronic cooling of the bosons. Our unified framework provides an intuitive way of understanding hybrid energy transport between electrons and bosons in their weak coupling limit. It opens the way of nonequilibrium reservoir engineering for efficient energy control between different quasi-particles at the nanoscale.

Quantum quenches in the Dicke model: Thermalization and failure of the generalized Gibbs ensemble

Xiao-Qiang Su(苏晓强) and You-Quan Zhao(赵有权)

Chin. Phys. B, 2020, 29 (12): 120506. DOI: 10.1088/1674-1056/abc679

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Quantum quenches in the Dicke model were studied both in the thermodynamic limit and the finite systems. For the integrable situation in the thermodynamic limit, the generalized Gibbs ensemble can effectively describe the energy-level occupations for the quench within the normal phase, but it fails for the quench to the superradiant phase. For the finite systems which are considered non-integrable, the post quench systems were studied by comparing with the thermal ensembles. The canonical ensembles are directly available for the quench within the normal phase. With the increasing of the target coupling strength over the equilibrium phase transition critical point, sudden changes take place for the effective temperature and the distance to the thermal ensembles. The thermalization was also studied by comparing with the results of the microcanonical ensembles.

Fiber cladding SPR bending sensor characterized by two parameters

Chunlan Liu(刘春兰), Jiangxi Hu(胡江西), Yong Wei(魏勇), Yudong Su(苏于东), Ping Wu(吴萍), Lingling Li(李玲玲), and Xiaoling Zhao(赵晓玲)

Chin. Phys. B, 2020, 29 (12): 120701. DOI: 10.1088/1674-1056/aba9c1

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A fiber cladding surface plasmon resonance (SPR) bending sensor is realized by the cladding of the fiber structure. By employing coating film, the sensing zone is protected and the toughness of the sensor increases. Three different sensing probes are tested, the experiment results indicate that the two parameters (wavelength sensitivity and light intensity sensitivity) sensing performances of the eccentric butt joint structures are superior to that of hetero-core structure, and the SPR bending sensor based on hetero-core structure is stable and uneasy to damage. By employing hetero-core fiber and silver film, a fiber cladding SPR bending sensor with better stabilization and sensing performance is realized. The proposed fabricating method of sensing probe with coating film provides a new approach for fiber SPR-distributed bending sensor.

Pressure-dependent physical properties of cubic Sr BO₃ ( B=Cr, Fe) perovskites investigated by density functional theory

Md Zahid Hasan, Md Rasheduzzaman, and Khandaker Monower Hossain

Chin. Phys. B, 2020, 29 (12): 123101. DOI: 10.1088/1674-1056/abab7f

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We perform the first-principles investigations of the structural, elastic, electronic, and optical properties of SrBO₃ (B =Cr, Fe) perovskites under pressure based on density functional theory (DFT). This is the first detailed pressure-dependent study of the physical properties for these compounds. The calculated structural parameters are consistent with the existing experimental results and slightly decrease with the application of pressure. The mechanical properties are discussed in detail and reveal that the SrCrO₃ is harder than SrFeO₃. Without pressure, these compounds behave like half-metals, confirmed by their band structure and density of states. Although the SrCrO₃ retains its half-metallic nature under pressure, SrFeO₃ becomes metallic for both up-spin and down-spin configuration. Both charge density and bond overlap population reveal the covalent nature of Cr-O bond and Fe-O bond in the studied compounds. The optical properties of SrBO₃, also discussed for the first time, reveal some interesting results.

Imprint of transient electron localization in H₂⁺ using circularly-polarized laser pulse Suggested by editors

Jianghua Luo(罗江华), Jun Li(李军), and Huafeng Zhang(张华峰)

Chin. Phys. B, 2020, 29 (12): 123201. DOI: 10.1088/1674-1056/abbbe1

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Photoelectron momentum distribution of hydrogen molecular ion in a circularly polarized laser pulse is calculated by solving the three-dimensional time-dependent Schrödinger equation (3D-TDSE). At the intermediate internuclear distance, an unusual multi-peak structure is observed in the angular distribution, which is proved to be a signature of the transient localization of the electron upon alternating nucleus. By tracing the time-dependent ionization rate and bound state populations, we provide a clear evidence that the transient electron localization still exists in circularly polarized pulse and the corresponding multiple ionization bursts are directly mapped onto observable angular distributions. In addition, we introduce an intuitive strong-field approximation model which incorporates laser-induced subcycle internal electron dynamics to isolate the effect of the Coulomb potential of the parent ions. In this way, the timing of each ionization burst can be directly read out from the angular distributions. Our results suggest that the ionization time serves as a sensitive tool encoding intramolecular electron dynamics and can be measured using attoclock technique.

Interference properties of a trapped atom interferometer in two asymmetric optical dipole traps

Li-Yong Wang(王立勇), Xiao Li(李潇), Kun-Peng Wang(王坤鹏), Yin-Xue Zhao(赵吟雪), Ke Di(邸克), Jia-Jia Du(杜佳佳), and Jian-Gong Hu(胡建功)

Chin. Phys. B, 2020, 29 (12): 123701. DOI: 10.1088/1674-1056/aba9c9

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We investigate interference properties of a trapped atom interferometer where two symmetric optical dipole traps (ODTs) act as the atomic wave-packets splitter and combiner with internal state labelling. After the preparation of initial superposition states, the atomic wave-packet is adiabatically split and moves into two spatially separate asymmetric ODTs. The atomic wave-packets in two ODTs are then adiabatically recombined after a duration of free evolving in traps, completing the interference cycle of this atom interferometer. We show that the interferogram exhibits a series of periodic revivals in interference visibility. Furthermore, the revival period decreases as the asymmetry of two dipole potentials increases. By introducing an echo sequence to the interferometer, we show that while the echo effect is not influenced by the asymmetry of the two ODTs, the onset of periodic revivals changes by the echo sequence. Our study provides an effective method to cancel or compensate the phase shift caused by position and time correlated force.

Two-step phase-shifting Fresnel incoherent correlation holography based on discrete wavelet transform

Meng-Ting Wu(武梦婷), Yu Zhang(张雨), Ming-Yu Tang(汤明玉), Zhi-Yong Duan(段智勇), Feng-Ying Ma(马凤英), Yan-Li Du(杜艳丽), Er-Jun Liang(梁二军), and Qiao-Xia Gong(弓巧侠)

Chin. Phys. B, 2020, 29 (12): 124201. DOI: 10.1088/1674-1056/abab7d

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Fresnel incoherent correlation holography (FINCH) has the ability to generate three-dimensional images with a super-resolution by using incoherent sources. However, there are unwanted direct current term and twin image in interferograms, so it is of great significance to find a method to eliminate them. Phase-shifting technology is a most widely used technique for this task, but its three-step phase-shifting is not suitable for the instantaneous measurement of dynamic objects, and the quality of reconstructed image with the traditional two-step phase-shifting is lower. In this paper, we present a method of enhancing the resolution through using a two-step phase-shifting technology based on the discrete wavelet transform. After two-step phase-shifting, the resulting hologram is a superposition of multiple forms. The frequency of the resulting hologram is decomposed into different levels through using discrete wavelet transform, then the image is reconstructed after retrieving the low frequency band. Various experiments have verified the effectiveness of this method.

Chaotic state as an output of vacuum state evolving in diffusion channel and generation of displaced chaotic state for quantum controlling

Feng Chen(陈锋), Wei Xiong(熊伟), Bao-Long Fang(方保龙) , and Hong-Yi Fan(范洪义)

Chin. Phys. B, 2020, 29 (12): 124202. DOI: 10.1088/1674-1056/abab81

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We show that chaotic state can be produced as an output of vacuum state evolving in diffusion channel, while displaced chaotic state is output of a coherent state evolving in diffusion channel. We also introduce the thermo vaccum state for the displaced chaotic state and evaluate the average photon number. The displaced chaotic state may be used exhibiting quantum controlling.

Quantum speed limit time and entanglement in a non-Markovian evolution of spin qubits of coupled quantum dots

M. Bagheri Harouni

Chin. Phys. B, 2020, 29 (12): 124203. DOI: 10.1088/1674-1056/abab75

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Quantum speed limit time and entanglement in a system composed of coupled quantum dots are investigated. The excess electron spin in each quantum dot constitutes the physical system (qubit). Also the spin interaction is modeled through the Heisenberg model and the spins are imposed by an external magnetic field. Taking into account the spin relaxation as a non-Markovian process, the quantum speed limit and entanglement evolution are discussed. Our findings reveal that increasing the magnetic field leads to the faster quantum evolution. In addition, the temperature increment causes the longer quantum speed limit time as well as the entanglement degradation.

High-dimensional atomic microscopy in surface plasmon polaritons

Akhtar Munir, Abdul Wahab, and Munsif Jan

Chin. Phys. B, 2020, 29 (12): 124204. DOI: 10.1088/1674-1056/abbbeb

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We develop a new scheme of two-dimensional (2D) and three-dimensional (3D) atom localization via absorption and gain spectra of surface plasmon polaritons (SPPs) in a closed loop four-level atomic system. For the atom-field interaction, we construct a spatially dependent field by superimposing two (three) standing-wave fields (SWFs) in 2D (3D) atom localization, respectively. We achieve high-precision and high spatial resolution of an atom localization by appropriately adjusting the system parameters such as probe field detuning and phase shifts of the SWFs. The absorption and gain spectra are used to attain information about the position of an atom in SPPs. Our proposed scheme opens up a fascinating way to improve the atom localization that supplies some practical applications in a high-dimensional SPPs.

High-precision three-dimensional atom localization via probe absorption at room temperature Suggested by editors

Mengmeng Luo(罗萌萌), Wenxiao Liu(刘文晓), Dingyu Cai(蔡定宇), and Shaoyan Gao(高韶燕)

Chin. Phys. B, 2020, 29 (12): 124205. DOI: 10.1088/1674-1056/abb3df

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A scheme is used to explore the behavior of three-dimensional (3D) atom localization in a Y-type hot atomic system. We can obtain the position information of the atom due to the position-dependent atom-field interaction. We study the influences of the system parameters and the temperature on the atom localization. More interestingly, the atom can be localized in a subspace when the temperature is equal to 323 K. Moreover, a method is proposed to tune multiparameter for localizing the atom in a subspace. The result is helpful to achieve atom nanolithography, photonic crystal and measure the center-of-mass wave function of moving atoms.

Generation of atomic spin squeezing via quantum coherence: Heisenberg-Langevin approach

Xuping Shao(邵旭萍)

Chin. Phys. B, 2020, 29 (12): 124206. DOI: 10.1088/1674-1056/abab7c

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Taking into account the dephasing process in the realistic atomic ensemble, we theoretically study the generation of atomic spin squeezing via atomic coherence induced by the coupling and probe fields. Using the Heisenberg-Langevin approach, we find that the perfect spin squeezing in the X component can be obtained while the coupling and probe fields produce the maximum coherence between the ground state sublevels 1 and 2. Moreover, the degree of atomic spin squeezing in the X component can be strengthened with the increasing atomic density and/or Rabi frequency of the mixing field. The theoretical results provide a proof-of-principle demonstration of generating the atomic spin squeezing via quantum coherence in the realistic atomic ensemble which may find potential applications in quantum information processing and quantum networks.

Realization of ultralow power phase locking by optimizing Q factor of resonant photodetector ^Hot!

Jin-Rong Wang(王锦荣), Hong-Yu Zhang(张宏宇), Zi-Lin Zhao(赵子琳), and Yao-Hui Zheng(郑耀辉)

Chin. Phys. B, 2020, 29 (12): 124207. DOI: 10.1088/1674-1056/abbbfb

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We design and construct a resonant photodetector (RPD) with a Q factor of 320.83 at the resonant frequency of 38.5 MHz on the basis of a theoretical analysis. Compared with the existing RPD under the same conditions, the signal-to-noise-ratio of the error signal is increased by 15 dB and the minimum operation power is reduced from -55 dBm to -70 dBm. By comparing the standard deviations of the stability curves, we confirm that the RPD has a dramatic improvement on ultralow power extraction. In virtue of the RPD, we have completed the demonstration of channel multiplexing quantum communication.

Compound-induced transparency in three-cavity coupled structure

Hao-Ye Qin(秦昊烨), Yi-Heng Yin(尹贻恒), and Ming Ding(丁铭)

Chin. Phys. B, 2020, 29 (12): 124208. DOI: 10.1088/1674-1056/abab7e

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We propose a three-cavity coupled cavity optomechanical (COM) structure with tunable system parameters and theoretically investigate the probe-light transmission rate. Numerical calculation of the system's spectra demonstrates distinctive compound-induced transparency (CIT) characteristics, including multiple transparency windows and sideband dips, which can be explained by a coupling between optomechanically-induced transparency (OMIT) and electromagnetically-induced transparency. The effects of optical loss (gain) in the cavity, number and topology of active cavity, tunneling ratio, and pump laser power on the CIT spectrum are evaluated and analyzed. Moreover, the optical group delay of CIT is highly controllable and fast-slow light inter-transition can be achieved. The proposed structure makes possible the advantageous tuning freedom and provides a potential platform for controlling light propagation and fast-slow light switching.

Effect of the distance between focusing lens and target surface on quantitative analysis of Mn element in aluminum alloys by using filament-induced breakdown spectroscopy

Xue-Tong Lu(陆雪童), Shang-Yong Zhao(赵上勇), Xun Gao(高勋), Kai-Min Guo(郭凯敏), and Jing-Quan Lin(林景全)

Chin. Phys. B, 2020, 29 (12): 124209. DOI: 10.1088/1674-1056/abb3ef

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Ultrafast laser filament-induced breakdown spectroscopy (FIBS) is a potential technique for quantitative analysis of trace elements. In this work, we investigate the effect of the distance between focusing lens and target surface on the FIBS quantitative analysis of Mn element in aluminum alloys, and several major parameters are calculated such as the linear correlation coefficient (R²), limits of detection (LOD), relative standard deviation (RSD), and root-mean-square error of cross-validations (RMSECV). The results show that the quantitative analysis parameter values before and after filament position are different. The optimal value can be obtained at the filament region, the average values of total 23 positions of R², LOD, RSD, and RMAECV were 99.45%, 1.41 mg/kg, 7.12%, and 0.56%, respectively. Besides, the spatial distributions of quantitative analysis parameter values in filament region are noticeable, and this is essentially due to intensity clamping effect in a filament.

Decoherence of fiber light sources using a single-trench fiber

Huahui Zhang(张华辉), Weili Zhang(张伟利), Zhao Wang(王昭), Hongyang Zhu(朱洪杨), Chao Yu(余超), Jiayu Guo(郭佳宇), Shanshan Wang(王珊珊), and Yunjiang Rao(饶云江)

Chin. Phys. B, 2020, 29 (12): 124210. DOI: 10.1088/1674-1056/abb65f

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Decoherence of fiber laser sources is of great importance in imaging applications, and most current studies use ordinary multi-mode fibers (MMFs). Here, a newly designed single-trench fiber (STF) is investigated to reduce the spatial coherence of fiber light source and compared with MMFs. By bending two fibers with different turns, speckle contrast of a 0.8-m-long STF can be reduced from 0.13 to 0.08, while a 0.8-m-long MMF shows an inverse result. Through speckle contrast and decoupling-mode analysis, the reason of this inverse trend is revealed. Firstly, the STF supports more modes than the MMF due to its larger core diameter. Secondly, mode leak from the first core of the STF can couple to the second core when bending the STF. Thus, power distribution among high and low-order modes become more even, reducing the spatial coherence considerably. However, in the MMF, high-order modes become leaky modes and decrease slightly when bending the fiber. This work provides a new method to modulate coherence of light source and a new angle to study decoherence principle using special fibers.

Interference effect on the liquid-crystal-based Stokes polarimeter Suggested by editors

Jun-Feng Hou(侯俊峰), Dong-Guang Wang(王东光), Yuan-Yong Deng(邓元勇), Zhi-Yong Zhang(张志勇), and Ying-Zi Sun(孙英姿)

Chin. Phys. B, 2020, 29 (12): 124211. DOI: 10.1088/1674-1056/abbbf4

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The Stokes polarimeter based on liquid crystal variable retarders (LCVRs) is envisaged as a promising novel technique for polarization measurement in space applications due to the inherent advantage of eliminating the need for conventional rotating polarizing optics and increasing the measuring speed. However, the intrinsic multi-beam interference in LCVRs limits its polarization accuracy by several percent. How to eliminate the influence of the interference effect becomes an urgent issue for the liquid-crystal-based Stokes polarimeter. The present study introduces a simplified but effective interference model based on the thin-film optics and polarized light theory to simulate the relationship between the interference effect of the LCVRs-based Stokes polarimeter and the polarization accuracy. The simulation results show that the transmittance variation of LCVR with the derived voltage is caused by multi beam interference between the indium tin oxide (ITO) film and the liquid crystal within LCVR, which produces a few percent of instrumental polarization. The instrumental polarization is about 0.01 and different for different wavelengths. An optimization method was proposed to reduce the instrumental polarization to 0.002, effectively improving the polarization sensitivity of the Stokes polarimeter limited by the interference. In addition, an experimental setup was built up to measure and analyze the influence of the interference effect of the LCVRs-based Stokes polarimeter on the polarization accuracy before and after the optimization. The experiment results are in good agreement with the simulation.

Absorption, quenching, and enhancement by tracer in acetone/toluene laser-induced fluorescence

Guang Chang(常光), Xin Yu(于欣), Jiangbo Peng(彭江波), Yang Yu(于杨), Zhen Cao(曹振), Long Gao(高龙), Minghong Han(韩明宏), and Guohua Wu(武国华)

Chin. Phys. B, 2020, 29 (12): 124212. DOI: 10.1088/1674-1056/abb3e1

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To measure the equivalent ratio distribution of the two-stage lean premixed (DLP) flame, we propose using acetone/toluene planar laser-induced fluorescence (PLIF) technology to simultaneously measure the concentrations of the two components. Appropriate excitation laser wavelength and filters are used to assess the influence of acetone and toluene on each other's fluorescence signal at room temperature. Experimental results show that acetone has a strong absorption effect on toluene's fluorescence signal, the effective absorption cross-section is 5.77× 10^-20 cm^-2. Acetone has an obvious quenching effect on the toluene fluorescence signal, and the Stern-Volmer coefficient is 0.50 kPa^-1. The collisions between the molecules of toluene and acetone will lead to the enhancement of the fluorescence signal of acetone, and the enhancement coefficient is exponential with the acetone's concentration. The quantitative relationship between the fluorescence intensity and the concentrations of the two tracers is obtained by establishing the photophysical model of toluene and acetone's fluorescence signals.

Nonclassicality of photon-modulated atomic coherent states in the Schwinger bosonic realization

Jisuo Wang(王继锁), Xiangguo Meng(孟祥国), and Xiaoyan Zhang(张晓燕)

Chin. Phys. B, 2020, 29 (12): 124213. DOI: 10.1088/1674-1056/abb3e8

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We theoretically introduce two new photon-modulated atomic coherent states (ACSs) via using the Schwinger bosonic representation of the angular momentum operators (the sequential operations Jⁿ) on an ACS, and investigate their nonclassicality using the Wigner distribution, photon number distribution, and entanglement entropy. It is found that photon-modulated ACSs possess more stronger nonclassicality than the original ACS in certain regions of τ , the nonclassicality enhances with increasing number n of the operations J and the operation J_+(-)ⁿ enhances the entanglement in the region of small (large) τ .

Impact vibration properties of locally resonant fluid-conveying pipes

Bing Hu(胡兵), Fu-Lei Zhu(朱付磊), Dian-Long Yu(郁殿龙), Jiang-Wei Liu(刘江伟), Zhen-Fang Zhang(张振方), Jie Zhong(钟杰), and Ji-Hong Wen(温激鸿)

Chin. Phys. B, 2020, 29 (12): 124301. DOI: 10.1088/1674-1056/abb312

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Fluid-conveying pipe systems are widely used in various equipments to transport matter and energy. Due to the fluid-structure interaction effect, the fluid acting on the pipe wall is easy to produce strong vibration and noise, which have a serious influence on the safety and concealment of the equipment. Based on the theory of phononic crystals, this paper studies the vibration transfer properties of a locally resonant (LR) pipe under the condition of fluid-structure interaction. The band structure and the vibration transfer properties of a finite periodic pipe are obtained by the transfer matrix method. Further, the different impact excitation and fluid-structure interaction effect on the frequency range of vibration attenuation properties of the LR pipe are mainly considered and calculated by the finite element model. The results show that the existence of a low-frequency vibration bandgap in the LR pipe can effectively suppress the vibration propagation under external impact and fluid impact excitation, and the vibration reduction frequency range is near the bandgap under the fluid-structure interaction effect. Finally, the pipe impact experiment was performed to verify the effective attenuation of the LR structure to the impact excitation, and to validate the finite element model. The research results provide a technical reference for the vibration control of the fluid-conveying pipe systems that need to consider blast load and fluid impact.

Calculation of radiative heat flux on irregular boundaries in participating media

Yu-Jia Sun(孙玉佳) and Shu Zheng(郑树)

Chin. Phys. B, 2020, 29 (12): 124401. DOI: 10.1088/1674-1056/abb22a

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Radiative heat flux at wall boundaries is important for its thermal design. Numerical methods based on structured grids are becoming trendy due to their simplicity and efficiency. Existing radiative transfer equation solvers produce oscillating radiative heat flux at the irregular boundary if they are based on structured grids. Reverse Monte Carlo method and analytical discrete ordinates method are adopted to calculate the radiative heat flux at complex boundaries. The results show that the reverse Monte Carlo method can generate a smooth radiative heat flux profile and it is smoother with larger energy bundles. The results from the analytical discrete ordinates method show that the fluctuations are due to the ray effect. For the total or the mean radiative heat flux, the results from the analytical discrete ordinates method are very close to those from the reverse Monte Carlo method.

A phononic rectifier based on carbon schwarzite host-guest system

Zhongwei Zhang(张忠卫), Yulou Ouyang(欧阳宇楼), Jie Chen(陈杰), and Sebastian Volz

Chin. Phys. B, 2020, 29 (12): 124402. DOI: 10.1088/1674-1056/abbbf9

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Thermal rectification is a promising way to manipulate the heat flow, in which thermal phonons are spectrally and collectively controlled. As phononic devices are mostly relying on monochromatic phonons, in this work we propose a phononic rectifier based on the carbon schwarzite host-guest system. By using molecular dynamic simulations, we demonstrate that the phononic rectification only happens at a specific frequency of the hybridized mode for the host-guest system, due to its strong confinement effect. Moreover, a significant rectification efficiency, ∼ 134 %, is observed, which is larger than most of the previously observed efficiencies. The study of length and temperature effects on the phononic rectification shows that the monochromaticity and frequency of the rectified thermal phonons depend on the intrinsic anharmonicity of the host-guest system and that the on-center rattling configuration with weak anharmonicity is preferable. Our study provides a new perspective on the rectification of thermal phonons, which would be important for controlling monochromatic thermal phonons in phononic devices.

The (3+1)-dimensional generalized mKdV-ZK equation for ion-acoustic waves in quantum plasmas as well as its non-resonant multiwave solution

Xiang-Wen Cheng(程香雯), Zong-Guo Zhang(张宗国), and Hong-Wei Yang(杨红卫)

Chin. Phys. B, 2020, 29 (12): 124501. DOI: 10.1088/1674-1056/abb3e2

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The quantum hydrodynamic model for ion-acoustic waves in plasmas is studied. First, we design a new disturbance expansion to describe the ion fluid velocity and electric field potential. It should be emphasized that the piecewise function perturbation form is new with great difference from the previous perturbation. Then, based on the piecewise function perturbation, a (3+1)-dimensional generalized modified Korteweg-de Vries Zakharov-Kuznetsov (mKdV-ZK) equation is derived for the first time, which is an extended form of the classical mKdV equation and the ZK equation. The (3+1)-dimensional generalized time-space fractional mKdV-ZK equation is constructed using the semi-inverse method and the fractional variational principle. Obviously, it is more accurate to depict some complex plasma processes and phenomena. Further, the conservation laws of the generalized time-space fractional mKdV-ZK equation are discussed. Finally, using the multi-exponential function method, the non-resonant multiwave solutions are constructed, and the characteristics of ion-acoustic waves are well described.

Alternative constitutive relation for momentum transport of extended Navier-Stokes equations

Guo-Feng Han(韩国锋), Xiao-Li Liu(刘晓丽), Jin Huang(黄进), Kumar Nawnit, and Liang Sun(孙亮)

Chin. Phys. B, 2020, 29 (12): 124701. DOI: 10.1088/1674-1056/abb3e5

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The classical Navier-Stokes equation (NSE) is the fundamental partial differential equation that describes the flow of fluids, but in certain cases, like high local density and temperature gradient, it is inconsistent with the experimental results. Some extended Navier-Stokes equations with diffusion terms taken into consideration have been proposed. However, a consensus conclusion on the specific expression of the additional diffusion term has not been reached in the academic circle. The models adopt the form of the generalized Newtonian constitutive relation by substituting the convection velocity with a new term, or by using some analogy. In this study, a new constitutive relation for momentum transport and a momentum balance equation are obtained based on the molecular kinetic theory. The new constitutive relation preserves the symmetry of the deviation stress, and the momentum balance equation satisfies Galilean invariance. The results show that for Poiseuille flow in a circular micro-tube, self-diffusion in micro-flow needs considering even if the local density gradient is very low.

Gravity-capillary waves modulated by linear shear flow in arbitrary water depth

Shaofeng Li(李少峰), Jinbao Song(宋金宝), and Anzhou Cao(曹安州)

Chin. Phys. B, 2020, 29 (12): 124702. DOI: 10.1088/1674-1056/abb3e4

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Considering that the fluid is inviscid and incompressible and the flow is irrotational in a fixed frame of reference and using the multiple scale analysis method, we derive a nonlinear Schrödinger equation (NLSE) describing the evolution dynamics of gravity-capillary wavetrains in arbitrary constant depth. The gravity-capillary waves (GCWs) are influenced by a linear shear flow (LSF) which consists of a uniform flow and a shear flow with constant vorticity. The modulational instability (MI) of GCWs with the LSF is analyzed using the NLSE. The MI is effectively modified by the LSF. In infinite depth, there are four asymptotes which are the boundaries between MI and modulational stability (MS) in the instability diagram. In addition, the dimensionless free surface elevation as a function of time for different dimensionless water depth, surface tension, uniform flow and vorticity is exhibited. It is found that the decay of free surface elevation and the steepness of free surface amplitude change over time, which are greatly affected by the water depth, surface tension, uniform flow and vorticity.

Revealing stepping forces in sub-mg tiny insect walking Suggested by editors

Yelong Zheng(郑叶龙), Wei Yin(尹维), Hongyu Lu(鲁鸿宇), and Yu Tian(田煜)

Chin. Phys. B, 2020, 29 (12): 124703. DOI: 10.1088/1674-1056/abb7ff

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Measuring walking forces of small or tiny insects can help the comprehension of their locomotion principles. However, as their size and force are generally too small, walking forces of small insects in sub-mg mass have never been actually measured. In this work, a convenient multi-lens and jelly surface based shadow method was developed for simultaneous multiple walking forces measuring, ranged from nN to mN with a sensitivity of sub-nN/pixel under ambient conditions. Walking force of six legs of a 0.3 mg water treader was demonstrated. The obtained results disclosed a rapid and extending middle leg strategy of water treader in walking forward above a jelly surface. This method is cost-effective and high-resolution, which could be easily used in measuring other tiny forces.

Electronic shell study of prolate Li_n(n =15-17) clusters: Magnetic superatomic molecules

Lijuan Yan(闫丽娟), Jianmei Shao(邵健梅), and Yongqiang Li(李永强)

Chin. Phys. B, 2020, 29 (12): 125101. DOI: 10.1088/1674-1056/abb669

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The non-spherical lowest-lying Li_n (n=15-17) isomers were found with high symmetric compact structures, of which the stability was not rationalized in a previous report (J. Chem. Phys. 119 9444 (2003)). Based on the newly proposed super-valence bond model, the three prolate lithium clusters can be viewed as magnetic superatomic molecules, which are composed by sharing valence electron pairs and nuclei between two superatom units, namely, Li₁₀ or Li₁₁, and thus their stability can be given a good understanding. Molecular orbital and chemical bonding analysis clearly reveal that the Li_n (n=15-17) clusters with prolate shapes are magnetic superatomic molecules. Our work may aid in the developments of the cluster-assembled materials or superatom-bonds.

Characteristics of DC arcs in a multi-arc generator and their application in the spheroidization of SiO₂ Suggested by editors

Qifu Lin(林启富), Yanjun Zhao(赵彦君), Wenxue Duan(段文学), Guohua Ni(倪国华), Xingyue Jin(靳兴月), Siyuan Sui(隋思源), Hongbing Xie(谢洪兵), and Yuedong Meng(孟月东)

Chin. Phys. B, 2020, 29 (12): 125201. DOI: 10.1088/1674-1056/ab9de9

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We investigate characteristics of multi-arc torches with three pairs of electrodes (three cathodes and three anodes) and their performance on the spheroidization of SiO₂ powder. The effect of electrode arrangement, including adjacent pattern (AD pattern, adjacent electrodes powered by one power supply) and opposite pattern (OP pattern, opposite electrodes powered by one power supply), on the dynamics of arc plasma is investigated based on synchronous acquisition of electrical and optical signals. The results show that both the voltage and spatial distribution of each arc of multiple arcs are more stable compared with those of a single arc. The fluctuation of an arc in multiple arcs mainly comes from the small-scale arc-to-arc restrikes among multiple arcs. Moreover, these arc-to-arc restrikes occur more frequently among multiple arc columns in OP pattern than in AD pattern. Moreover, the high-temperature area of the central region of arc chamber in OP pattern is larger than that in AP pattern. For the spheroidization of SiO₂ in this multi-arc generator, the spheronization degrees of plasma treated silica in OP pattern are at least 20% higher than those in AD pattern.

Propagation properties of the chirped Airy-Gaussian vortex electron plasma wave

Lican Wu(吴利灿), Jinhong Wu(吴锦鸿), Yujun Liu(刘煜俊), and Dongmei Deng(邓冬梅)

Chin. Phys. B, 2020, 29 (12): 125202. DOI: 10.1088/1674-1056/aba9cc

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We introduce a new class of the chirped Airy-Gaussian vortex electron plasma (CAiGVEP) wave which constitutes the exact and continuous transition modes between the chirped Airy vortex and the chirped Gaussian vortex electron plasma wave. The intensity, the phase, and the angular momentum density flow of the CAiGVEP wave are discussed under different distribution factors and different chirp modes.

Anti-oxidation characteristics of Cr-coating on surface of Ti-45Al-8.5Nb alloy by plasma surface metallurgy technique

Bing Zhou(周兵), Ya-Rong Wang(王亚榕), Ke Zheng(郑可), Yong Ma(马永), Yong-Sheng Wang(王永胜), Sheng-Wang Yu(于盛旺), and Yu-Cheng Wu(吴玉程)

Chin. Phys. B, 2020, 29 (12): 126101. DOI: 10.1088/1674-1056/aba9c2

Abstract ( 350 )

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TiAl-based alloys have received extensive attention recently due to their excellent properties. However, the weak oxidation resistance at temperatures higher than 800 ^°C can limit their further high-temperature structural applications. To improve the oxidation resistance of a high-Nb-content γ -TiAl alloy (Ti-45Al-8.5Nb, in units of at.%), a chromium (Cr) coating is prepared by using the plasma surface alloying technique, separately, at 800 ^°C and 1000 ^°C. The x-ray diffraction (XRD) patterns reveal that an oxide surface layer consisting of Cr₂O₃, Al₂O₃, and TiO₂ is produced on the Cr-coated Nb containing γ -TiAl substrates during the initial oxidation. However, the Cr₂O₃ is dominated in the oxide surface layer after being isothermally oxidized for 300 h. The oxidation kinetic curves are composed of a parabolic law stage ( ≤ 90 h) and a biquadratic law stage ( ≥ 90 h), fit by weight-gain curves. Due to diffusion in the fabrication process and oxidation process, the Cr-coated specimens have an adhesion force after being isothermally oxidized, specifically 69 N for a specimen after oxidation for 300 h. These results demonstrate that the Cr coating enhances the oxidation resistance and adhesion of a Ti-45Al-8.5Nb alloy, which may provide a new feasible scheme for designing oxidation protection layers.

Nonperturbative effects of attraction on dynamical behaviors of glass-forming liquids Suggested by editors

Xiaoyan Sun(孙晓燕), Haibo Zhang(张海波), Lijin Wang(王利近), Zexin Zhang(张泽新), and Yuqiang Ma(马余强)\ccclink

Chin. Phys. B, 2020, 29 (12): 126201. DOI: 10.1088/1674-1056/abbbdd

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We investigate systematically the effects of the inter-particle attraction on the structure and dynamical behaviors of glass-forming liquids via molecular dynamics simulations. We find that the inter-particle attraction does not influence the structure, but greatly affects the dynamics and dynamical heterogeneity of the system. After the system changes from a purely repulsive glass-forming liquid to an attractive one, the dynamics slows down and the dynamical heterogeneity becomes greater, which is found interestingly to be associated with larger cooperative rearrangement regions (CRRs). Additionally, the structures of CRRs are observed to be compact in attractive glass-forming liquids but string-like in purely repulsive ones. Our findings constitute an important contribution to the ongoing study of the role of attractions in properties of glasses and glass-forming liquids.

Electronic structure and optical properties of Ge-and F-doped α -Ga₂O₃: First-principles investigations

Ti-Kang Shu(束体康), Rui-Xia Miao(苗瑞霞), San-Dong Guo(郭三栋), Shao-Qing Wang(王少青), Chen-He Zhao(赵晨鹤), and Xue-Lan Zhang(张雪兰)

Chin. Phys. B, 2020, 29 (12): 126301. DOI: 10.1088/1674-1056/abbbff

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The prospect of α -Ga₂O₃in optical and electrical devices application is fascinating. In order to obtain better performance, Ge and F elements with similar electronegativity and atomic size are selected as dopants. Based on density functional theory (DFT), we systematically research the electronic structure and optical properties of doped α -Ga₂O₃ by GGA+U calculation method. The results show that Ge atoms and F atoms are effective n-type dopants. For Ge-doped α -Ga₂O₃, it is probably obtained under O-poor conditions. However, for F-doped α -Ga₂O₃, it is probably obtained under O-rich conditions. The doping system of F element is more stable due to the lower formation energy. In this investigation, it is found that two kinds of doping can reduce the α -Ga₂O₃ band gap and improve the conductivity. What is more, it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region. Through the whole scale of comparison, Ge doping is more suitable for the application of transmittance materials, yet F doping is more appropriate for the application of deep ultraviolet devices. We expect that our research can provide guidance and reference for preparation of α -Ga₂O₃ thin films and photoelectric devices.

Jamming in confined geometry: Criticality of the jamming transition and implications of structural relaxation in confined supercooled liquids Suggested by editors

Jun Liu(柳军), Hua Tong(童华), Yunhuan Nie(聂运欢), and Ning Xu(徐宁)

Chin. Phys. B, 2020, 29 (12): 126302. DOI: 10.1088/1674-1056/abc160

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In marginally jammed solids confined by walls, we calculate the particle and ensemble averaged value of an order parameter, $\left<\varPsi(r)\right>$, as a function of the distance to the wall, r. Being a microscopic indicator of structural disorder and particle mobility in solids, $\varPsi$ is by definition the response of the mean square particle displacement to the increase of temperature in the harmonic approximation and can be directly calculated from the normal modes of vibration of the zero-temperature solids. We find that, in confined jammed solids, $\left<\varPsi(r)\right>$ curves at different pressures can collapse onto the same master curve following a scaling function, indicating the criticality of the jamming transition. The scaling collapse suggests a diverging length scale and marginal instability at the jamming transition, which should be accessible to sophisticatedly designed experiments. Moreover, $\left<\varPsi(r)\right>$ is found to be significantly suppressed when approaching the wall and anisotropic in directions perpendicular and parallel to the wall. This finding can be applied to understand the r-dependence and anisotropy of the structural relaxation in confined supercooled liquids, providing another example of understanding or predicting behaviors of supercooled liquids from the perspective of the zero-temperature amorphous solids.

Reduction of interfacial thermal resistance of overlapped graphene by bonding carbon chains

Yuwen Huang(黄钰文), Wentao Feng(冯文韬), Xiaoxiang Yu(余晓翔), Chengcheng Deng(邓程程), and Nuo Yang(杨诺)

Chin. Phys. B, 2020, 29 (12): 126303. DOI: 10.1088/1674-1056/abc677

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Exploring the mechanism of interfacial thermal transport and reducing the interfacial thermal resistance are of great importance for thermal management and modulation. Herein, the interfacial thermal resistance between overlapped graphene nanoribbons is largely reduced by adding bonded carbon chains as shown by molecular dynamics simulations. And the analytical model (phonon weak couplings model, PWCM) is utilized to analyze and explain the two-dimensional thermal transport mechanism at the cross-interface. An order of magnitude reduction of the interfacial thermal resistance is found as the graphene nanoribbons are bonded by just one carbon chain. Interestingly, the decreasing rate of the interfacial thermal resistance slows down gradually with the increasing number of carbon chains, which can be explained by the proposed theoretical relationship based on analytical model. Moreover, by the comparison of PWCM and the traditional simplified model, the accuracy of PWCM is demonstrated in the overlapped graphene nanoribbons. This work provides a new way to improve the interfacial thermal transport and reveal the essential mechanism for low-dimensional materials applied in thermal management.

Low lattice thermal conductivity and high figure of merit in p-type doped K₃IO

Weiqiang Wang(王巍强), Zhenhong Dai(戴振宏), Qi Zhong(钟琦), Yinchang Zhao(赵银昌), and Sheng Meng(孟胜)

Chin. Phys. B, 2020, 29 (12): 126501. DOI: 10.1088/1674-1056/abab83

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Based on first-principles calculations, Boltzmann transport equation and semiclassical analysis, we conduct a detailed study on the lattice thermal conductivity $\kappa_\rm L$, Seebeck coefficient S, electrical conductivity σ, power factor S²σ and dimensionless figure of merit, zT, for K₃IO. It is found that K₃IO exhibits relatively low lattice thermal conductivity of 0.93 Wm^-1K^-1 at 300 K, which is lower than the value 1.26 Wm^-1K^-1 of the classical TE material PbTe. This is due to the smaller phonon group velocity Ν_g and smaller relaxation time τ_Λ. The low lattice thermal conductivity can lead to excellent thermoelectric properties. Thus maximum zT of 2.87 is obtained at 700 K, and the zT=0.41 at 300 K indicate that K₃IO is a potential excellent room temperature TE material. Our research on K₃IO shows that it has excellent thermoelectric properties, and it is a promising candidate for applications in fields in terms of thermoelectricity.

Tuning thermal transport via phonon localization in nanostructures

Dengke Ma(马登科), Xiuling Li(李秀玲), and Lifa Zhang(张力发)

Chin. Phys. B, 2020, 29 (12): 126502. DOI: 10.1088/1674-1056/abb7fa

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Localization, one of the basic phenomena for wave transport, has been demonstrated to be an effective strategy to manipulate electronic, photonic, and acoustic properties of materials. Due to the wave nature of phonons, the tuning of thermal properties through phonon localization would also be expected, which is beneficial to many applications such as thermoelectrics, electronics, and phononics. With the development of nanotechnology, nanostructures with characteristic length about ten nanometers can give rise to phonon localization, which has attracted considerable attention in recent years. This review aims to summarize recent advances with theoretical, simulative, and experimental studies toward understanding, prediction, and utilization of phonon localization in disordered nanostructures, focuses on the effect of phonon localization on thermal conductivity. Based on previous researches, perspectives regarding further researches to clarify this hectic-investigated and immature topic and its exact effect on thermal transport are given.

Lattice thermal conductivity of β₁₂ and χ₃ borophene

Jia He(何佳), Yulou Ouyang(欧阳宇楼), Cuiqian Yu(俞崔前), Pengfei Jiang(蒋鹏飞), Weijun Ren(任卫君), and Jie Chen(陈杰)

Chin. Phys. B, 2020, 29 (12): 126503. DOI: 10.1088/1674-1056/abbbe6

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Borophene allotropes have many unique physical properties due to their polymorphism and similarity between boron and carbon. In this work, based on the density functional theory and phonon Boltzmann transport equation, we investigate the lattice thermal conductivity $\kappa $ of both β ₁₂ and χ₃ borophene. Interestingly, these two allotropes with similar lattice structures have completely different thermal transport properties. β₁₂ borophene has almost isotropic $\kappa $ around 90 W/(mK) at 300 K, while $\kappa $ of χ₃ borophene is much larger and highly anisotropic. The room temperature $\kappa $ of χ ₃ borophene along the armchair direction is 512 W/(mK), which is comparable to that of hexagonal boron nitride but much higher than most of the two-dimensional materials. The physical mechanisms responsible for such distinct thermal transport behavior are discussed based on the spectral phonon analysis. More interestingly, we uncover a unique one-dimensional transport feature of transverse acoustic phonon in χ₃ borophene along the armchair direction, which results in a boost of phonon relaxation time and thus leads to the significant anisotropy and ultrahigh thermal conductivity in χ₃ borophene. Our study suggests that χ ₃ borophene may have promising application in heat dissipation, and also provides novel insights for enhancing the thermal transport in two-dimensional systems.

Evaporation of nanoscale water on solid surfaces

Rongzheng Wan(万荣正) and Haiping Fang(方海平)

Chin. Phys. B, 2020, 29 (12): 126601. DOI: 10.1088/1674-1056/abc0d3

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The evaporation of water is essential in the macroscopic world. Recent researches show that, on solid surfaces, the evaporation of nanoscale water is quite different from that on bulk water surfaces. In this review, we show the theoretical progress in the study of nanoscale water evaporation on various solid surfaces: the evaporation rate of nanoscale water does not show a monotonic decrease when the solid surface changes from hydrophobic to hydrophilic; the evaporation of nanoscale water on hydrophobic-hydrophilic patterned surfaces is unexpectedly faster than that on uniform surface; the evaporation of nanoscale water on patterned graphene oxide is faster than that on homogeneous one; how temperature affects the evaporation of nanoscale water on solid surface; how ions affect the evaporation of nanoscale water on graphene oxide.

Temperature-dependent Gilbert damping in Co₂ FeAl thin films with different B2 ordering degrees

Gesang Dunzhu(格桑顿珠), Yi-Bing Zhao(赵逸冰), Ying Jin(金莹), Cai Zhou(周偲), and Chang-Jun Jiang(蒋长军)

Chin. Phys. B, 2020, 29 (12): 126701. DOI: 10.1088/1674-1056/abb231

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The temperature-dependent Gilbert damping in Co₂FeAl thin film grown on a Pb(Mg_{1 / 3}Nb_{2 / 3})O₃-30%PbTiO₃ substrate is investigated by the systematic measurement of physical property measurement system (PPMS) on a series of samples with different substrate temperatures. Varying the substrate temperatures from 350 ^°C to 500 ^°C, the B2 ordering degrees of Co₂FeAl thin films increase, which can lead the Gilbert damping to decrease, indicated by the field-sweep in-plane PPMS measurements. In addition, the measurement result of PPMS demonstrates that the Gilbert damping decreases first with measurement temperature decreasing down to about 150 K, then increases at a measurement temperature of ∼ 50 K, and decreases again with the measurement temperature decreasing. There are two independent damping manners, namely bulk damping and surface damping, which contribute to the Gilbert damping. Moreover, the observed peak of Gilbert damping at ∼ 50 K can be attributed to the spin re-orientation transition at the Co₂FeAl surface, which is similar to the result of the effective magnetization as a function of measurement temperature. The result presents the evidence for further studying the Gilbert damping in Co₂FeAl thin film.

Characterization and optimization of AlGaN/GaN metal-insulator semiconductor heterostructure field effect transistors using supercritical CO₂/H₂O technology

Meihua Liu(刘美华), Zhangwei Huang(黄樟伟), Kuan-Chang Chang(张冠张), Xinnan Lin(林信南), Lei Li(李蕾), and Yufeng Jin(金玉丰)

Chin. Phys. B, 2020, 29 (12): 127101. DOI: 10.1088/1674-1056/abb22f

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The impact of supercritical CO₂/H₂O technology on the threshold-voltage instability of AlGaN/GaN metal-insulator semiconductor high-electron-mobility transistors (MIS-HEMTs) is investigated. The MIS-HEMTs were placed in a supercritical fluid system chamber at 150 ^°C for 3 h. The chamber was injected with CO₂ and H₂O at pressure of 3000 psi (1 psi≈6.895 kPa). Supercritical H₂O fluid has the characteristics of liquid H₂O and gaseous H₂O at the same time, that is, high penetration and high solubility. In addition, OH^- produced by ionization of H₂O can fill the nitrogen vacancy near the Si₃N₄/GaN/AlGaN interface caused by high temperature process. After supercritical CO₂/H₂O treatment, the threshold voltage shift is reduced from 1 V to 0.3 V. The result shows that the threshold voltage shift of MIS-HEMTs could be suppressed by supercritical CO₂/H₂O treatment.

Density wave and topological superconductivity in the magic-angle-twisted bilayer-graphene

Ming Zhang(张铭), Yu Zhang(张渝), Chen Lu(卢晨), Wei-Qiang Chen(陈伟强), and Fan Yang(杨帆)

Chin. Phys. B, 2020, 29 (12): 127102. DOI: 10.1088/1674-1056/abc7b5

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The model dependence in the study of the magic-angle twisted bilayer-graphene (MA-TBG) is an important issue in the research area. It has been argued previously that the two-band tight-binding (TB) model (per spin and valley) cannot serve as a start point for succeeding studies as it cannot correctly describe the topological aspect of the continuum-theory model near the Dirac nodes in the mini Brillouin zone (MBZ). For this purpose, we adopt the faithful TB model [Phys. Rev. B 99 195455 (2019)] with five bands (per spin and valley) as our start point, which is further equipped with extended Hubbard interactions. Then after systematic random-phase-approximation (RPA) based calculations, we study the electron instabilities of this model, including the density wave (DW) and superconductivity (SC), near the van Hove singularity (VHS). Our results are as follows. In the case neglecting the tiny inter-valley exchange interaction, the exact $SU(2)_K\times SU(2)_K'$ symmetry leads to the degeneracy between the inter-valley charge DW (CDW) and the spin DW (SDW) (which would be mixed then), and that between the singlet $d+id$-wave and triplet $p+ip$-wave topological SCs. When a realistic tiny inter-valley exchange interaction is turned on with nonzero coefficient (J_H≠ 0), the SDW or CDW is favored respectively at the critical point, determined by $J_\rm H\to 0^-$ or $J_\rm H\to 0^+$. In the mean time, the degeneracy between the singlet $d+id$-wave and triplet $p+ip$-wave topological SCs is also lifted up by the tiny J_H. These results are highly similar to the results of our previous study [arXiv:2003.09513] adopting the two-band TB model, with the reason lying in that both models share the same symmetry and Fermi-surface (FS) nesting character near the VHS. Such a similarity suggests that the low-energy physics of the doped MA-TBG is mainly determined by the symmetry and the shape of the FS of the doped system, and is insensitive to other details of the band structure, including the topological aspects near the Dirac nodes in the MBZ.

Different noncollinear magnetizations on two edges of zigzag graphene nanoribbons

Yang Xiao(肖杨), Qiaoli Ye(叶巧利), Jintao Liang(梁锦涛), Xiaohong Yan(颜晓红), and Ying Zhang(张影)

Chin. Phys. B, 2020, 29 (12): 127201. DOI: 10.1088/1674-1056/abc0e4

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Based on density functional theory and non-equilibrium Green's function method, we studied noncollinear magnetism and spin transport in a 180^° domain wall made of zigzag graphene nanoribbon (ZGNR) with different noncollinear magnetic profiles on the top and bottom edges. Our results show that a helical domain wall on the top (bottom) edge and an abrupt domain wall on the bottom (top) edge can survive in the ZGNR. This indicates that such characteristic magnetization distribution can be obtained by some means, e.g., the introduction of impurity on one edge. Compared to a wide ZGNR, a narrow ZGNR presents obvious coupling between the two edges which changes the magnetization and transmission greatly. As for the above-mentioned distinct magnetic profile, the spin transport is blocked in the abrupt domain wall due to strong spin flip scattering while remains unaffected in the helical domain wall due to the spin mixing effect. We deduce a formula of the transmission for various magnetic profiles of the ZGNRs. A new result based on this formula is that the transmission at the Fermi level can be zero, one, and two by tuning the edge magnetization. Our results provide insights into the noncollinear spin transport of the ZGNR-based devices.

Bound in continuum states and induced transparency in mesoscopic demultiplexer with two outputs

Z Labdouti, T Mrabti, A Mouadili, E H El Boudouti, F Fethi, and B Djafari-Rouhani

Chin. Phys. B, 2020, 29 (12): 127301. DOI: 10.1088/1674-1056/abad23

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We investigate the electronic transport in a simple mesoscopic cross structure made of two wires (stubs) grafted at the same point along a quantum waveguide. We show that the structure may exhibit important phenomena such as bound in continuum (BIC) states. These states are transformed into electromagnetically induced transparency (EIT) resonance by detuning slightly the lengths of the stubs. The last phenomenon is used to propose and study a mesoscopic demultiplexer device with an input waveguide and two output waveguides. We give closed-form expressions of the geometrical parameters that allow a selective transfer of a given state in the first waveguide without perturbing the second waveguide. The effect of temperature on the transmission resonances is also examined by using Landauer-Büttiker formula. The analytical results of the dispersion relation and transmission and reflection coefficient are obtained using the Green's function method.

Electron dynamics of active mode-locking terahertz quantum cascade laser

Qiushi Hou(侯秋实), Chang Wang(王长), and Juncheng Cao(曹俊诚)

Chin. Phys. B, 2020, 29 (12): 127302. DOI: 10.1088/1674-1056/abc0da

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The pulse generation from active mode-locking terahertz quantum cascade laser is studied by Maxwell-Bloch equations. It is shown that longer dephasing time will lead to multiple pulses generation from the laser. The dependence of output field on modulation length and radio-frequency parameters is obtained. In order to achieve short pulse generation, the DC bias should close to threshold value and modulation length should be shorter than 0.256 mm. The output pulse is unstable and the envelope shows many oscillations in the presence of spatial hole burning, resulting destabilization of mode-locking.

Tunable metal-insulator transition in LaTiO₃/CaVO₃ superlattices: A theoretical study

Ya-Kui Weng(翁亚奎), Meng-Lan Shen(沈梦兰), Jie Li(李杰), and Xing-Ao Li(李兴鳌)

Chin. Phys. B, 2020, 29 (12): 127303. DOI: 10.1088/1674-1056/abc237

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As one of intriguing physical results of electronic reconstruction, the metal-insulator transition plays an important role in exploring new electronic devices. In this study, the density functional theory is employed to investigate the metal-insulator transition in (LaTiO₃)_m/(CaVO₃)_n superlattices. Herein, three kinds of physical avenues, i.e., stacking orientation, epitaxial strain, and thickness periods, are used to tune the metal-insulator transition. Our calculations find that the [001]-and [110]-oriented (LaTiO₃)₁/(CaVO₃)₁ superlattices on SrTiO₃ substrate are insulating, while [111]-oriented case is metallic. Such metallic behavior in [111] orientation can also be modulated by epitaxial strain. Besides the structural orientation and strain effect, the highly probable metal-insulator transition is presented in (LaTiO₃)_m/(CaVO₃)_n superlattices with increasing thickness. In addition, several interesting physical phenomena have also been revealed, such as selective charge transfer, charge ordering, and orbital ordering.

Progress on band structure engineering of twisted bilayer and two-dimensional moirè heterostructures

Wei Yao(姚维), Martin Aeschlimann, and Shuyun Zhou(周树云)

Chin. Phys. B, 2020, 29 (12): 127304. DOI: 10.1088/1674-1056/abc7b6

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Artificially constructed van der Waals heterostructures (vdWHs) provide an ideal platform for realizing emerging quantum phenomena in condensed matter physics. Two methods for building vdWHs have been developed: stacking two-dimensional (2D) materials into a bilayer structure with different lattice constants, or with different orientations. The interlayer coupling stemming from commensurate or incommensurate superlattice pattern plays an important role in vdWHs for modulating the band structures and generating new electronic states. In this article, we review a series of novel quantum states discovered in two model vdWH systems -graphene/hexagonal boron nitride (hBN) hetero-bilayer and twisted bilayer graphene (tBLG), and discuss how the electronic structures are modified by such stacking and twisting. We also provide perspectives for future studies on hetero-bilayer materials, from which an expansion of 2D material phase library is expected.

Multiple reversals of vortex ratchet effects in a superconducting strip with inclined dynamic pinning landscape

An He(何安) and Cun Xue(薛存)

Chin. Phys. B, 2020, 29 (12): 127401. DOI: 10.1088/1674-1056/abbbe5

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Using time-dependent Ginzburg-Landau formalism, we investigate the multiple reversals of ratchet effects in an unpatterned superconducting strip by the tilted dynamic pinning potential. In the case of collinear sliding potential and Lorentz force, vortices are always confined in the channels induced by sliding potential. However, due to the inclination angle of sliding pinning potential with respect to the Lorentz force, vortices could be driven out of the channels, and unexpected results with multiple reversals of vortex rectifications are observed. The mechanism of multiple reversals of vortex rectifications is explored by analyzing different vortex motion scenarios with increasing ac current amplitudes. The multiple reversals of transverse and longitudinal ratchet effects can be highly controlled by ac amplitude and dynamic pinning velocity. What's more, at certain large current the ratchet effect reaches strongest within a wide range of pinning sliding velocity.

Phase-field simulation of superconductor vortex clustering in the vicinity of ferromagnetic domain bifurcations

Hasnain Mehdi Jafri, Jing Wang(王静), Chao Yang(杨超), Jun-Sheng Wang(王俊升), and Hou-Bing Huang(黄厚兵)

Chin. Phys. B, 2020, 29 (12): 127402. DOI: 10.1088/1674-1056/abb22c

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Superconductors and ferromagnets are highly non-compatible materials due to the natures of their respective electronic states. But when artificially brought together, they develop interesting characteristics, one of which, vortex clustering, is discussed here in this paper. Phase-field and micromagnetic simulations are performed to investigate the superconductor and ferromagnet bilayer, respectively. The ferromagnet with uniaxial anisotropy is observed to develop the maze domain, whereas the superconductor subjected to the influence of the ferromagnetic stray field displays a vortex pattern. Clustered vortices in superconductors at certain locations are observed to be precisely located over magnetic domain bifurcations. The enhanced out-of-plane stray field at bifurcations around the curved domain walls and the convergent Lorentz force due to screening currents in superconductor are attributed to the formation of clusters at bifurcation sites. Segregation of the inter-vortex spacing between straight and bifurcated domain is clearly observed. More importantly, inter-vortex spacing is predicted to serve as a precise tool to map local ferromagnet domain shapes.

Thermal stability and thermoelectric properties of Cd-doped nano-layered Cu₂Se prepared using NaCl flux method

Jianhua Lu(陆建华), Decong Li(李德聪), Wenting Liu(刘文婷), Lanxian Shen(申兰先), Jiali Chen(陈家莉), Wen Ge(葛文), and Shukang Deng(邓书康)

Chin. Phys. B, 2020, 29 (12): 127403. DOI: 10.1088/1674-1056/abbbf5

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Cu₂Se is a promising "phonon liquid-electron crystal" thermoelectric material with excellent thermoelectric performance. In this work, Cd-doped Cu_{2 -x}SeCd_x (x = 0, 0.0075, 0.01, and 0.02) samples were prepared using NaCl flux method. The solubility of Cd in Cu₂Se at room temperature was less than 6%, and a second phase of CdSe was found in the samples with large initial Cd content (x = 0.01 and 0.02). Field-emission scanning electron microscopic image showed that the arranged lamellae formed a large-scale layered structure with an average thickness of approximately 100 nm. Transmission electron microscopy demonstrated that doping of Cd atoms did not destroy the crystal integrity of Cu₂Se. A small amount of Cd in Cu₂Se could reduce the electrical and thermal conductivities of the material, thus significantly enhancing its thermoelectric performance. With the increase in Cd content in the sample, the carrier concentration decreased and the mobility increased gradually. Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point. Excessive Cd doping led to the emergence of the second phase of CdSe in the sample, thus significantly increasing the thermal conductivity of the material. A maximum ZT value of 1.67 at 700 K was obtained in the Cu_1.9925SeCd_0.0075 sample.

Structural and electrical transport properties of Cu-doped Fe_{1 -x}Cu_xSe single crystals ^Hot!

He Li(李贺), Ming-Wei Ma(马明伟), Shao-Bo Liu(刘少博), Fang Zhou(周放), and Xiao-Li Dong(董晓莉)

Chin. Phys. B, 2020, 29 (12): 127404. DOI: 10.1088/1674-1056/abc3af

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We report the structural and electrical transport properties of Fe_{1 -x}Cu_xSe (x = 0, 0.02, 0.05, 0.10) single crystals grown by a chemical vapor transport method. Substituting Cu for Fe suppresses both the nematicity and superconductivity of FeSe single crystal, and provokes a metal-insulator transition. Our Hall measurements show that the Cu substitution also changes an electron dominance at low temperature of un-doped FeSe to a hole dominance of Cu-doped Fe_{1 -x}Cu_xSe at x = 0.02 and 0.1, and reduces the sign-change temperature (T_R) of the Hall coefficient (R_H).

Improvement of the low-field-induced magnetocaloric effect in EuTiO₃ compounds

Shuang Zeng(曾爽), Wen-Hao Jiang(姜文昊), Hui Yang(杨慧), Zhao-Jun Mo(莫兆军) Jun Shen(沈俊), and Lan Li(李岚)

Chin. Phys. B, 2020, 29 (12): 127501. DOI: 10.1088/1674-1056/abb230

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The magnetocaloric effect of Mn, Ni, and Mn-Ni-doped EuTiO₃ compounds are studied in the near-liquid-helium-temperature range. The Eu(Ti_0.9375Mn_0.0625)O₃, Eu(Ti_0.975Ni_0.025)O₃, and Eu(Ti_0.9125Mn_0.0625Ni_0.025)O₃ are prepared by the sol-gel method. The Eu(Ti_0.9375Mn_0.0625)O₃ and Eu(Ti_0.9125Mn_0.0625Ni_0.025)O₃ exhibit ferromagnetism with second-order phase transition, and the Eu(Ti_0.975Ni_0.025)O₃ displays antiferromagnetic behavior. Under the magnetic field change of 10 kOe (1 Oe=79.5775 Am^-1), the values of magnetic entropy change are 8.8 Jkg^-1K^-1, 12 Jkg^-1K^-1, and 10.9 Jkg^-1K^-1 for Eu(Ti_0.9375Mn_0.0625)O₃, Eu(Ti_0.975Ni_0.025)O₃, and Eu(Ti_0.9125Mn_0.0625Ni_0.025)O₃, respectively. The co-substitution of Mn and Ni can not only improve the magnetic entropy change, but also widen the refrigeration temperature window, which greatly enhances the magnetic refrigeration capacity. Under the magnetic field change of 10 kOe, the refrigerant capacity value of Eu(Ti_0.9125Mn_0.0625Ni_0.025)O₃ is 62.6 Jkg^-1 more than twice that of EuTiO₃ (27 Jkg^-1), indicating that multi-component substitution can lead to better magnetocaloric performance.

Crystal structure and electromagnetic responses of tetragonal GdAlGe Suggested by editors

Cong Wang(王聪), Yong-Quan Guo(郭永权), Tai Wang(王泰), and Shuo-Wang Yang(杨硕望)

Chin. Phys. B, 2020, 29 (12): 127502. DOI: 10.1088/1674-1056/abad25

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The ternary rare-earth aluminum germanide GdAlGe with tetragonal structure is systematically studied by x-ray diffraction, magnetic and electric measurements. The magnetic and electric properties of GdAlGe are strongly related to its special magnetic structure formed by magnetic Gd3 isosceles triangles $\vartriangle $s. The GdAlGe orders ferromagnetically at 21 K due to the exchanging interaction of Gd3 $\vartriangle \uparrow $-$\vartriangle \uparrow $ Gd3. The mechanism of magnetic transport originates from the slip scattering induced by Stoner spin fluctuation in the magnetic ordering region and the spin wave scattering induced by the thermal photon excitation and phonon scattering in the paramagnetic region. The positive magnetoresistance is observed in GdAlGe, which might be due to the disordered magnetic scatter induced by magnetic anisotropy in GdAlGe.

A novel high breakdown voltage and high switching speed GaN HEMT with p-GaN gate and hybrid AlGaN buffer layer for power electronics applications

Yong Liu(刘勇), Qi Yu(于奇), and Jiang-Feng Du(杜江锋)

Chin. Phys. B, 2020, 29 (12): 127701. DOI: 10.1088/1674-1056/abaee5

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A novel p-GaN gate GaN high-electron-mobility transistor (HEMT) with an AlGaN buffer layer and hybrid dielectric zone (H-HEMT) is proposed. The hybrid dielectric zone is located in the buffer and composed of horizontal arranged HfO₂ zone and SiN_x zone. The proposed H-HEMT is numerically simulated and optimized by the Silvaco TCAD tools (ATLAS), and the DC, breakdown, C-V and switching properties of the proposed device are characterized. The breakdown voltage of the proposed HEMT is significantly improved with the introduction of the hybrid dielectric zone, which can effectively modulate the electric field distribution in the GaN channel and the buffer. High breakdown voltage of 1490 V, low specific on-state resistance of 0.45 mΩ cm² and high Baliga's figure of merit (FOM) of 5.3 GW/cm², small R_onQ_oss of 212 mΩ nC, high turn-on speed 627 V/ns and high turn-off speed 87 V/ns are obtained at the same time with the gate-to-drain distance L_gd of 6 μ m.

Improved water oxidation via Fe doping of CuWO₄ photoanodes: Influence of the Fe source and concentration

Yue Sun(孙岳), Fenqi Du(杜粉琦), Donghang Xie(谢东航), Dongmei Yang(杨冬梅), Yang Jiao(焦阳), Lichao Jia(贾丽超), and Haibo Fan(范海波)

Chin. Phys. B, 2020, 29 (12): 127801. DOI: 10.1088/1674-1056/aba9cb

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Iron (Fe) was successfully doped in CuWO₄ photoanode films with a combined liquid-phase spin-coating method via the dopant sources of Fe(NO₃)₃, FeSO₄ and FeCl₃. The microstructure of the prepared films was characterized by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The light absorption and photoelectric conversion properties were evaluated by the UV-visible absorption spectra and monochromatic incident photon-to-electron conversion efficiency. The chemical composition and element combination of the samples were examined by x-ray photoelectron spectroscopy. A linear sweep voltammetric and stability test (I-t) were performed with an electrochemical workstation. The results show that the samples are uniform with a thickness of approximately 800 nm and that the photoelectrochemical performance of the doped films is heavily dependent on the Fe source and dopant concentration. Upon optimizing the doping conditions of Fe(NO₃)₃ and the optimal source, the photocurrent density in the Fe-doped CuWO₄ photoanode film is improved by 78% from 0.267 mA/cm² to 0.476 mA/cm² at 1.23 V vs reversible hydrogen electrode. The underlying causes are discussed.

Photoluminescence of green InGaN/GaN MQWs grown on pre-wells

Shou-Qiang Lai(赖寿强), Qing-Xuan Li(李青璇), Hao Long(龙浩), Jin-Zhao Wu(吴瑾照), Lei-Ying Ying(应磊莹), Zhi-Wei Zheng(郑志威), Zhi-Ren Qiu(丘志仁), and Bao-Ping Zhang(张保平)

Chin. Phys. B, 2020, 29 (12): 127802. DOI: 10.1088/1674-1056/abb65b

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Photoluminescence (PL) characteristics of the structure consisting of green InGaN/GaN multiple quantum wells (MQWs) and low indium content InGaN/GaN pre-wells are investigated. Several PL peaks from pre-wells and green InGaN/GaN MQWs are observed. The peak energy values for both pre-wells and green InGaN/GaN MQWs display an S-shaped variation with temperature. In addition, the differences in the carrier localization effect, defect density, and phonon-exciton interaction between the pre-wells and green InGaN/GaN MQWs, and the internal quantum efficiency of the sample are studied. The obtained results elucidate the mechanism of the luminescence characteristics of the sample and demonstrate the significant stress blocking effect of pre-wells.

Atomistic study on tensile fracture of densified silica glass and its dependence on strain rate

Zhi-Qiang Hu(胡志强), Jian-Li Shao(邵建立), Yi-Fan Xie(谢轶凡), and Yong Mei(梅勇)

Chin. Phys. B, 2020, 29 (12): 128101. DOI: 10.1088/1674-1056/abb3f2

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Densification is a major feature of silica glass that has received widespread attention. This work investigates the fracture behavior of densified silica glass upon uniaxial tension based on atomistic simulations. It is shown that the tensile strength of the silica glass approximately experiences a parabolic reduction with the initial density, while the densified samples show a faster power growth with the increase of strain rate. Meanwhile, the fracture strain and strain energy increase significantly when the densification exceeds a certain threshold, but fracture strain tends to the same value and strain energy becomes closer for different densified samples at extreme high strain rate. Microscopic views indicate that all the cracks are formed by the aggregation of nanoscale voids. The transition from brittleness fracture to ductility fracture can be found with the increase of strain rate, as a few fracture cracks change into a network distribution of many small cracks. Strikingly, for the high densified sample, there appears an evident plastic flow before fracture, which leads to the crack number less than the normal silica glass at the high strain rate. Furthermore, the coordinated silicon analysis suggests that high strain rate tension will especially lead to the transition from 4-to 3-fold Si when the high densified sample is in plastic flow.

Morphological modifications of C₆₀ crystal rods under hydrothermal conditions

Ming-Run Du(杜明润), Shi-Xin Liu(刘士鑫), Jia-Jun Dong(董家君), Ze-Peng Li(李泽朋), Ming-Chao Wang (王明超), Tong Wei(魏通), Qing-Jun Zhou(周青军), Xiong Yang(杨雄), and Peng-fei Shen(申鹏飞)

Chin. Phys. B, 2020, 29 (12): 128102. DOI: 10.1088/1674-1056/abc0d8

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We observed morphological modification of rod-shaped C₆₀ solvate crystals using a facile hydrothermal method. The initial C₆₀ rods were changed from smooth rods to rough rods, porous rods or pieces under different hydrothermal conditions. During the hydrothermal treatment, the initial samples underwent a decomposition-recrystallization process, which can be tuned by the content of alcohol in the hydrothermal solution, thereby leading to modification of the morphological properties of the initial C₆₀ rods. In addition, the rough and porous C₆₀ rods prepared in our work exhibit excellent photoluminescence intensities that are approximately 7 and 3 times higher than those of pure C₆₀ powders, respectively. Our results suggest that the hydrothermal method is a potential route for fabricating fullerene materials with controllable morphologies and novel functions.

Effects of MgSiO₃ on the crystal growth and characteristics of type-Ib gem quality diamond in Fe-Ni-C system Suggested by editors

Zhi-Yun Lu(鲁智云), Yong-Kui Wang(王永奎), Shuai Fang(房帅), Zheng-Hao Cai(蔡正浩), Zhan-Dong Zhao(赵占东), Chun-Xiao Wang(王春晓), Hong-An Ma(马红安), Liang-Chao Chen(陈良超), and Xiao-Peng Jia(贾晓鹏)

Chin. Phys. B, 2020, 29 (12): 128103. DOI: 10.1088/1674-1056/abb800

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We report the effects of MgSiO₃ addition on the crystal growth and characteristics of type-Ib diamonds synthesized in Fe-Ni-C system. The experiments were carried out with pressure at 5.5 GPa, temperature at 1385 ^°C-1405 ^°C, and duration of 23.1 h. As MgSiO₃ increases from 0.0 wt% to 3.0 wt%, the diamond growth temperature increases from 1385 ^°C to 1405 ^°C, the addition of MgSiO₃ and the movement of P-T diagram toward the higher temperature direction result in a series of effects to the Fe-Ni-C system and crystal growth. Firstly, it increases the content of metastable recrystallized graphite and accelerates the competition with the carbon source needed for diamond growth, thus causing the decreased crystal growth rate. Diamond crystals exhibit the combination form of {111}, {100}, {113}, and {110} sectors, the decreased {100} and {113} sectors, dominated {111} sector are all attributed to the higher growth rate in [100] direction caused by the synergy of MgSiO₃ and the movement of P-T diagram. The higher growth rate in [100] direction also increases the metal catalyst and graphite inclusions and leads to the increase of residual tensile stress on the crystal surface. Accompanying with the high growth rate, a higher dissolution rate along [100] and [113] directions than [111] direction occurs at the microstructure and forms the significantly developed (111) stepped growth layer. In addition to the movement of P-T diagram, the addition of MgSiO₃ poisons the catalyst and increases the nitrogen content of diamond from 120 ppm to 227 ppm.

A review of experimental advances in twisted graphene moirè superlattice

Yanbang Chu(褚衍邦), Le Liu(刘乐), Yalong Yuan(袁亚龙), Cheng Shen(沈成), Rong Yang(杨蓉), Dongxia Shi(时东霞), Wei Yang(杨威), and Guangyu Zhang(张广宇)

Chin. Phys. B, 2020, 29 (12): 128104. DOI: 10.1088/1674-1056/abb221

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Twisted moirè superlattice receives tremendous interests since the discovery of correlated insulating states and superconductivity in magic angle twist bilayer graphene (MA-TBG) [Nature 556 80 (2018), Nature 556 43 (2018)], even gives arise to a new field "twistronics" [Science 361 690 (2018)]. It is a new platform hosting strong electron correlations, providing an alternative for understanding unconventional superconductivity. In this article, we provide a review of recent experimental advances in the twisted moirè superlattice, from MA-TBG to twisted double bilayer graphene and other two-dimensional materials based moirè superlattice, covering correlated insulating states, superconductivity, magnetism, et al.

Effect of grain boundary energy anisotropy on grain growth in ZK60 alloy using a 3D phase-field modeling

Yu-Hao Song(宋宇豪), Ming-Tao Wang(王明涛), Jia Ni(倪佳), Jian-Feng Jin(金剑锋), and Ya-Ping Zong(宗亚平)

Chin. Phys. B, 2020, 29 (12): 128201. DOI: 10.1088/1674-1056/abad1f

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A three-dimensional (3D) multiple phase field model, which takes into account the grain boundary (GB) energy anisotropy caused by texture, is established based on real grain orientations and Read-Shockley model. The model is applied to the grain growth process of polycrystalline Mg (ZK60) alloy to investigate the evolution characteristics in different systems with varying proportions of low-angle grain boundary (LAGB) caused by different texture levels. It is found that the GB energy anisotropy can cause the grain growth kinetics to change, namely, higher texture levels (also means higher LAGB proportion) result in lower kinetics, and vice versa. The simulation results also show that the topological characteristics, such as LAGB proportion and distribution of grain size, undergo different evolution characteristics in different systems, and a more serious grain size fluctuation can be caused by a higher texture level. The mechanism is mainly the slower evolution of textured grains in their accumulation area and the faster coarsening rate of non-textured grains. Therefore, weakening the texture level is an effective way for implementing a desired homogenized microstructure in ZK60 Mg alloy. The rules revealed by the simulation results should be of great significance for revealing how the GB anisotropy affects the evolution of polycrystalline during the grain growth after recrystallization and offer the ideas for processing the alloy and optimizing the microstructure.

Performance optimization of self-powered visible photodetectors based on Cu₂O/electrolyte heterojunctions

Zhi-Ming Bai(白智明), Ying-Hua Zhang(张英华), Zhi-An Huang(黄志安), Yu-Kun Gao(高玉坤), and Jia Liu(刘佳)

Chin. Phys. B, 2020, 29 (12): 128202. DOI: 10.1088/1674-1056/abab7b

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The performance of the self-powered photodetectors based on the Cu₂O/electrolyte heterojunctions is optimized by adjusting morphology and structure of the Cu₂O film. The Cu₂O film with a deposition time of 2000 s possesses a largest current density of 559.6 μ A/cm² under visible light illumination at zero bias, with a rising time of 5.2 ms and a recovering time of 9.0 ms. This optimized Cu₂O film has a highest responsivity of about 25.8 mA/W for visible light, and a negligible responsivity for UV light. The high crystallinity and excellent charge transfer property are responsible for the improved photodetection performance.

Compact NbN resonators with high kinetic inductance ^Hot!

Xing-Yu Wei(魏兴雨), Jia-Zheng Pan(潘佳政), Ya-Peng Lu(卢亚鹏), Jun-Liang Jiang(江俊良), Zi-Shuo Li(李子硕), Sheng Lu(卢盛), Xue-Cou Tu(涂学凑), Qing-Yuan Zhao(赵清源), Xiao-Qing Jia(贾小氢), Lin Kang(康琳), Jian Chen(陈健), Chun-Hai Cao(曹春海), Hua-Bing Wang(王华兵), Wei-Wei Xu(许伟伟), Guo-Zhu Sun(孙国柱), and Pei-Heng Wu(吴培亨)

Chin. Phys. B, 2020, 29 (12): 128401. DOI: 10.1088/1674-1056/abc2b8

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We design and fabricate Λ/2 coplanar waveguide NbN resonators, the thickness and length of which are only several nanometers and hundred microns, respectively. The quality factor of such compact resonators can reach up to 7.5×10⁴ at single photon power level at 30 mK with the resonance frequency around 6.835 GHz. In order to tune the resonant frequency, the resonator is terminated to the ground with a dc-SQUID. By tuning the magnetic flux in the dc-SQUID, the effective inductance of the dc-SQUID is varied, which leads to the change in the resonant frequency of the resonator. The tunability range is more than 30 MHz and the quality factor is about 3×10³. These compact and tunable NbN resonators have potential applications in the quantum information processing, such as in the precision measurement, coupling and/or reading out the quantum states of qubits.

PBTI stress-induced 1/ f noise in n-channel FinFET

Dan-Yang Chen(陈丹旸), Jin-Shun Bi(毕津顺), Kai Xi(习凯), and Gang Wang(王刚)

Chin. Phys. B, 2020, 29 (12): 128501. DOI: 10.1088/1674-1056/abaee4

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The influence of positive bias temperature instability (PBTI) on 1/f noise performance is systematically investigated on n-channel fin field-effect transistor (FinFET). The FinFET with long and short channel (L=240 nm, 16 nm respectively) is characterized under PBTI stress from 0 s to 10⁴ s. The 1/f noise features are analyzed by using the unified physical model taking into account the contributions from the carrier number and channel mobility fluctuations. The I_d-V_g, I_d-V_d, I_g-V_g tests are conducted to support and verify the physical analysis in the PBTI process. It is found that the influence of the channel mobility fluctuations may not be neglected. Due to the mobility degradation in a short-channel device, the noise level of the short channel device also degrades. Trapping and trap generation regimes of PBTI occur in high-k layer and are identified based on the results obtained for the gate leakage current and 1/f noise.

A 2DEG back-gated graphene/AlGaN deep-ultraviolet photodetector with ultrahigh responsivity Suggested by editors

Jinhui Gao(高金辉), Yehao Li(李叶豪), Yuxuan Hu(胡宇轩), Zhitong Wang(王志通), Anqi Hu(胡安琪), and Xia Guo(郭霞)\ccclink

Chin. Phys. B, 2020, 29 (12): 128502. DOI: 10.1088/1674-1056/abb3eb

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A graphene/AlGaN deep-ultraviolet (UV) photodetector is presented with ultrahigh responsivity of 3.4×10⁵ A/W at 261 nm incident wavelength and 149 pW light power. A gain mechanism based on electron trapping at the potential well is proposed to be responsible for the high responsivity. To optimize the trade-off between responsivity and response speed, a back-gate electrode is designed at the AlGaN/GaN two-dimensional electron gas (2DEG) area which eliminates the persistent photocurrent effect and shortens the recovery time from several hours to milliseconds. The 2DEG gate is proposed as an alternative way to apply the back gate electrode on AlGaN based devices on insulating substrates. This work sheds light on a possible way for weak deep-UV light detection.

Reliability of organic light-emitting diodes in low-temperature environment ^Hot!

Saihu Pan(潘赛虎), Zhiqiang Zhu(朱志强), Kangping Liu(刘康平), Hang Yu(于航), Yingjie Liao(廖英杰), Bin Wei(魏斌), Redouane Borsali, and Kunping Guo(郭坤平)

Chin. Phys. B, 2020, 29 (12): 128503. DOI: 10.1088/1674-1056/abc154

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Organic light-emitting diode (OLED) is an electroluminescent technology that relies on charge-carrier dynamics and is a potential light source for variable environmental conditions. Here, by exploiting a self-developed low-temperature testing system, we investigated the characteristics of hole/electron transport, electro-optic conversion efficiency, and operation lifetime of OLEDs at low-temperature ranging from -40 ^°C to 0 ^°C and room temperature (25 ^°C). Compared to devices operating at room temperature, the carrier transport capability is significantly decreased with reducing temperature, and especially the mobility of the hole-transporting material (HTM) and electron-transporting material (ETM) at -40 ^°C decreases from 1.16× 10^-6 cm²/Vs and 2.60× 10^-4 cm²/Vs to 6.91× 10^-9 cm²/Vs and 1.44× 10^-5 cm²/Vs, respectively. Indeed, the temperature affects differently on the mobilities of HTM and ETM, which favors unbalanced charge-carrier transport and recombination in OLEDs, thereby leading to the maximum current efficiency decreased from 6.46 cdA^-1 at 25 ^°C to 2.74 cdA^-1 at -40 ^°C. In addition, blue fluorescent OLED at -20 ^°C has an above 56% lifetime improvement (time to 80% of the initial luminance) over the reference device at room temperature, which is attributed to efficiently dissipating heat generated inside the device by the low-temperature environment.

Tail-structure regulated phase behaviors of a lipid bilayer Suggested by editors

Wenwen Li(李文文), Zhao Lin(林召), Bing Yuan(元冰), and Kai Yang(杨恺)\ccclink

Chin. Phys. B, 2020, 29 (12): 128701. DOI: 10.1088/1674-1056/abad20

Abstract ( 365 )

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Lateral heterogeneity of a cell membrane, including the formation of lipid raft-like clusters and the inter-leaflet coupling of specific phase domains, is crucial for cellular functions such as membrane trafficking and transmembrane signaling. However, the wide diversity in lipid species and the consequent complexity in lipid-lipid interplays hinder our understanding of the underlying mechanism. In this work, with coarse-grained molecular dynamics simulations, the effect of lipid tail structures on the phase behavior of a model ternary lipid membrane was systematically explored. A serial of 27 lipid membrane systems consisting of saturated, unsaturated lipids, and cholesterol (Chol) molecules, at a fixed molar ratio of 4:4:2 while varying in lipid structures including tail length, unsaturation degree, and/or position of unsaturated atoms, were constructed. These structural factors were found to exert sophisticated influences on packing states of the constituent molecules, especially Chol, in a bilayer, and modulate the complicated entropy-enthalpy competition of the membrane system accordingly. Specifically, an appropriate difference in effective tail length and distinct feature of the tail ends between the saturated and unsaturated lipid compositions promised an enhanced phase separation of the membrane into the Chol-rich Lo and Chol-poor Ld phase domains, with a full inter-leaflet coupling of each domain. Our results provide insights into the lipid organizations and segregations of the cellular plasma membrane.

Enhanced vibrational resonance in a single neuron with chemical autapse for signal detection Suggested by editors

Zhiwei He(何志威), Chenggui Yao(姚成贵), Jianwei Shuai(帅建伟), and Tadashi Nakano

Chin. Phys. B, 2020, 29 (12): 128702. DOI: 10.1088/1674-1056/abb7f9

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Many animals can detect the multi-frequency signals from their external surroundings. The understanding for underlying mechanism of signal detection can apply the theory of vibrational resonance, in which the moderate high frequency driving can maximize the nonlinear system's response to the low frequency subthreshold signal. In this work, we study the roles of chemical autapse on the vibrational resonance in a single neuron for signal detection. We reveal that the vibrational resonance is strengthened significantly by the inhibitory autapse in the neuron, while it is weakened typically by the excitatory autapse. It is generally believed that the inhibitory synapse has a suppressive effect in neuronal dynamics. However, we find that the detection of the neuron to the low frequency subthreshold signal can be improved greatly by the inhibitory autapse. Our finding indicates that the inhibitory synapse may act constructively on the detection of weak signal in the brain and neuronal system.

Dielectric properties of nucleated erythrocytes as simulated by the double spherical-shell model Suggested by editors

Jia Xu(徐佳), Weizhen Xie(谢伟珍), Yiyong Chen(陈一勇), Lihong Wang(王立洪), and Qing Ma(马青)

Chin. Phys. B, 2020, 29 (12): 128703. DOI: 10.1088/1674-1056/abbbf0

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The dielectric properties of nucleated erythrocytes from bullfrogs were measured in a frequency range of 10 kHz-110 MHz. The complex permittivity (ε^*), complex conductivity ($\kappa^*$), and complex resistivity (ρ^*) were analyzed and compared in the 10.63% to 37.58% haematocrit (Hct) range. The relaxation behavior, the passive electrical properties, and the cellular structure parameters, including the cell membrane, the cytoplasm, the nuclear membrane, and the nucleoplasm of the nucleated erythrocyte suspensions were investigated. The method used is based on the binomial Cole-Cole equation and the double spherical-shell physical models. Upon the elimination of the electrode polarization effect, two definite relaxations related to the interfacial polarization are observed on low-and high-frequency dispersions. The permittivity values and the characteristic frequency values differ by one order of magnitude: the low-frequency relaxation increments [∆ ε ₁= (5.63 1.43)× 10³] and the characteristic frequency [f_c1= (297.06 14.48) kHz] derived from the cell membrane, the high-frequency relaxation increments [∆ ε ₂ =(5.21 1.20)× 10²] and the characteristic frequency [f_c2=(3.73 0.06) MHz] derived from the dielectric response to the external electric field of the nuclear membrane, respectively. Moreover, the other core dielectric parameters, such as the relative permittivity of the cell membrane [ε_m= (7.57 0.38)] and the nuclear envelope [ε_ne= (23.59 4.39)], the conductivity of the cytoplasm (hemoglobin, $\kappa_\rm Hb= (0.50 \pm 0.13)$ S/m] and the nuclear endoplasm [$\kappa_\rm np= (2.56 \pm 0.75)$ S/m], and the capacitance of the bilayer membranes [C_m: (0.84 0.04) μ F/cm²], and C_ne: (0.52 0.10) μ F/cm²] were also accurately and reliably measured. This work presents a feasible method to evaluate the dielectric parameters and the cellular structure of the erythrocytes of bullfrogs. Moreover, it paves the way for new studies on the haematology of frogs and the detection of nucleated cells via dielectric impedance spectroscopy.

Super-resolution filtered ghost imaging with compressed sensing Suggested by editors

Shao-Ying Meng(孟少英), Wei-Wei Shi(史伟伟), Jie Ji(季杰), Jun-Jie Tao(陶俊杰), Qian Fu(付强), Xi-Hao Chen(陈希浩), and Ling-An Wu(吴令安)

Chin. Phys. B, 2020, 29 (12): 128704. DOI: 10.1088/1674-1056/abc15f

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A filtered ghost imaging (GI) protocol is proposed that enables the Rayleigh diffraction limit to be exceeded in an intensity correlation system; a super-resolution reconstructed image is achieved by low-pass filtering of the measured intensities. In a lensless GI experiment performed with spatial bandpass filtering, the spatial resolution can exceed the Rayleigh diffraction bound by more than a factor of 10. The resolution depends on the bandwidth of the filter, and the relationship between the two is investigated and discussed. In combination with compressed sensing programming, not only high resolution can be maintained but also image quality can be improved, while a much lower sampling number is sufficient.

A 9% efficiency of flexible Mo-foil-based Cu₂ZnSn(S, Se)₄ solar cells by improving CdS buffer layer and heterojunction interface

Quan-Zhen Sun(孙全震), Hong-Jie Jia(贾宏杰), Shu-Ying Cheng(程树英), Hui Deng(邓辉)\ccclink, Qiong Yan(严琼), Bi-Wen Duan(段碧雯), Cai-Xia Zhang(张彩霞), Qiao Zheng(郑巧), Zhi-Yuan Yang(杨志远), Yan-Hong Luo(罗艳红), Qing-Bo Men(孟庆波), and Shu-Juan Huang(黄淑娟)

Chin. Phys. B, 2020, 29 (12): 128801. DOI: 10.1088/1674-1056/abb7fe

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Flexible Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells show great potential applications due to low-cost, nontoxicity, and stability. The device performances under an especial open circuit voltage (V_OC) are limited by the defect recombination of CZTSSe/CdS heterojunction interface. We improve the deposition technique to obtain compact CdS layers without any pinholes for flexible CZTSSe solar cells on Mo foils. The efficiency of the device is improved from 5.7% to 6.86% by highquality junction interface. Furthermore, aiming at the S loss of CdS film, the S source concentration in deposition process is investigated to passivate the defects and improve the CdS film quality. The flexible Mo-foil-based CZTSSe solar cells are obtained to possess a 9.05% efficiency with a V_OC of 0.44 V at an optimized S source concentration of 0.68 mol/L. Systematic physical measurements indicate that the S source control can effectively suppress the interface recombination and reduce the V_OC deficit. For the CZTSSe device bending characteristics, the device efficiency is almost constant after 1000 bends, manifesting that the CZTSSe device has an excellent mechanical flexibility. The effective improvement strategy of CdS deposition is expected to provide a new perspective for promoting the conversion efficiency of CZTSSe solar cells.

Modularity-based representation learning for networks

Jialin He(何嘉林), Dongmei Li(李冬梅), and Yuexi Liu(刘阅希)

Chin. Phys. B, 2020, 29 (12): 128901. DOI: 10.1088/1674-1056/abbbec

Abstract ( 402 )

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Network embedding aims at learning low-dimensional representation of vertexes in a network and effectively preserving network structures. These representations can be used as features for many complex tasks on networks such as community detection and multi-label classification. Some classic methods based on the skip-gram model have been proposed to learn the representation of vertexes. However, these methods do not consider the global structure ( i.e., community structure) while sampling vertex sequences in network. To solve this problem, we suggest a novel sampling method which takes community information into consideration. It first samples dense vertex sequences by taking advantage of modularity function and then learns vertex representation by using the skip-gram model. Experimental results on the tasks of community detection and multi-label classification show that our method outperforms three state-of-the-art methods on learning the vertex representations in networks.

Shortest path of temporal networks: An information spreading-based approach

Yixin Ma(马一心), Xiaoyu Xue(薛潇雨), Meng Cai(蔡萌), and Wei Wang(王伟)

Chin. Phys. B, 2020, 29 (12): 128902. DOI: 10.1088/1674-1056/abb302

Abstract ( 420 )

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The shortest path is a widely studied network science problem and has attracted great attention. Nevertheless, it draws little attention in temporal networks, in which temporal edges determine information dissemination. In this paper, we propose an information spreading-based method to calculate the shortest paths distribution in temporal networks. We verify our method on both artificial and real-world temporal networks and obtain a good agreement. We further generalize our method to identify influential nodes and found an effective method. Finally, we verify the influential nodes identifying method on four networks.

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