中国物理B

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Brownian ratchet mechanism of translocation in T7 RNA polymerase facilitated by a post-translocation energy bias arising from the conformational change of the enzyme

王展峰, 张志强, 付一本, 王鹏业, 谢平

2017 (3): 30201-030201. doi: 10.1088/1674-1056/26/3/030201

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T7 RNA polymerase can transcribe DNA to RNA by translocating along the DNA. Structural studies suggest that the pivoting rotation of the O helix in the fingers domain may drive the movement of the O helix C-terminal Tyr639 from pre- to post-translocation positions. In a series of all-atom molecular dynamics simulations, we show that the movement of Tyr639 is not tightly coupled to the rotation of the O helix, and that the two processes are only weakly dependent on each other. We also show that the internal potential of the enzyme itself generates a small difference in free energy (ΔE) between the post- and pre-translocation positions of Tyr639. The calculated value of ΔE is consistent with that obtained from single-molecule experimental data. These findings lend support to a model in which the translocation takes place via a Brownian ratchet mechanism, with the small free energy bias ΔE arising from the conformational change of the enzyme itself.

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Residual symmetry, interaction solutions, and conservation laws of the (2+1)-dimensional dispersive long-wave system

夏亚荣, 辛祥鹏, 张顺利

2017 (3): 30202-030202. doi: 10.1088/1674-1056/26/3/030202

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We explore the (2+1)-dimensional dispersive long-wave (DLW) system. From the standard truncated Painlevé expansion, the Bäcklund transformation (BT) and residual symmetries of this system are derived. The introduction to an appropriate auxiliary dependent variable successfully localizes the residual symmetries to Lie point symmetries. In particular, it is verified that the (2+1)-dimensional DLW system is consistent Riccati expansion (CRE) solvable. If the special form of (CRE)-consistent tanh-function expansion (CTE) is taken, the soliton-cnoidal wave solutions and corresponding images can be explicitly given. Furthermore, the conservation laws of the DLW system are investigated with symmetries and Ibragimov theorem.

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Meshless analysis of an improved element-free Galerkin method for linear and nonlinear elliptic problems

唐耀宗, 李小林

2017 (3): 30203-030203. doi: 10.1088/1674-1056/26/3/030203

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We first give a stabilized improved moving least squares (IMLS) approximation, which has better computational stability and precision than the IMLS approximation. Then, analysis of the improved element-free Galerkin method is provided theoretically for both linear and nonlinear elliptic boundary value problems. Finally, numerical examples are given to verify the theoretical analysis.

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Modes splitting in graphene-based double-barrier waveguides

有四普, 何英, 杨艳芳, 张惠芳

2017 (3): 30301-030301. doi: 10.1088/1674-1056/26/3/030301

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The graphene-based double-barrier waveguides induced by electric field have been investigated. The guided modes can only exist in the case of Klein tunneling, and the fundamental mode is absent. The guided modes in the single-barrier waveguide split into symmetric and antisymmetric modes with different incident angles in the double-barrier waveguide. The phase difference between electron states and hole states is also discussed. The phase difference for the two splitting modes is close to each other and increases with the order of guided modes. These phenomena can be helpful for the potential applications in graphene-based optoelectronic devices.

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Two-step quantum secure direct communication scheme with frequency coding

赵学亮, 李俊林, 牛鹏皓, 马鸿洋, 阮东

2017 (3): 30302-030302. doi: 10.1088/1674-1056/26/3/030302

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Quantum secure direct communication (QSDC) is an important branch of quantum cryptography. It can transmit secret information directly without establishing a key first, unlike quantum key distribution which requires this precursory event. Here we propose a QSDC scheme by applying the frequency coding technique to the two-step QSDC protocol, which enables the two-step QSDC protocol to work in a noisy environment. We have numerically simulated the performance of the protocol in a noisy channel, and the results show that the scheme is indeed robust against channel noise and loss. We also give an estimate of the channel noise upper bound.

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Rapidly calculating the partition function of macroscopic systems

李菁田, 宁博元, 龚乐诚, 庄军, 宁西京

2017 (3): 30501-030501. doi: 10.1088/1674-1056/26/3/030501

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It has remained an open problem to accurately compute the partition function of macroscopic systems since the establishment of statistical physics. A rapid method approaching this problem was presented and was strictly tested by molecular dynamic (MD) simulations on Ar atoms in both dense gaseous and liquid states. The outcomes from the method on the internal energy and the work of isothermal expansion (and therefore the free energy) are in good agreement with the MD simulations, suggesting the method would be immediately applied in vast areas.

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Homoclinic and heteroclinic chaos in nonlinear systems driven by trichotomous noise

雷佑铭, 张红霞

2017 (3): 30502-030502. doi: 10.1088/1674-1056/26/3/030502

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The homoclinic and heteroclinic chaos in nonlinear systems subjected to trichotomous noise excitation are studied. The Duffing system and the Josephson-junction system are taken for example to calculate the corresponding amplitude thresholds for the onset of chaos on the basis of the stochastic Melnikov process with the mean-square criterion. It is shown that the amplitude threshold for the onset of chaos can be adjusted by changing the internal parameters of trichotomous noise, thereby inducing or suppressing chaotic behaviors in the two systems driven by trichotomous noise. The effects of trichotomous noise on the systems are verified by vanishing the mean largest Lyapunov exponent and demonstrated by phase diagrams and time histories.

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Effects of time delays in a mathematical bone model

王莉芳, 仇康, 贾亚

2017 (3): 30503-030503. doi: 10.1088/1674-1056/26/3/030503

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In this paper we propose a mathematical model of bone remodeling with time delays of both osteoclast-derived paracrine signaling of tumor and tumor-derived paracrine signaling of osteoclast. The effects of time delays on the growth of tumor cells and bone system are studied in multiple myeloma-induced bone disease. In the case of small osteoclast-derived paracrine signaling, it is found that the growth of tumor cells slows down, the oscillation period of the ratio of osteoclasts to osteoblasts is extended with increasing time delay, and there is a competition between the delay and osteoclast-derived paracrine signaling. In the case of large tumor-derived paracrine signaling, the tumor-derived paracrine signaling can induce a more significant decline in tumor growth for long time delay, and thus slowing down the progression of bone disease. There is an optimal coupling between the tumor-derived paracrine signaling of osteoclasts and time delay during the progressions of bone diseases, which suppresses the tumor growth and the regression of bone disease.

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Adaptive fuzzy synchronization for a class of fractional-order neural networks

刘恒, 李生刚, 王宏兴, 李冠军

2017 (3): 30504-030504. doi: 10.1088/1674-1056/26/3/030504

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In this paper, synchronization for a class of uncertain fractional-order neural networks with external disturbances is discussed by means of adaptive fuzzy control. Fuzzy logic systems, whose inputs are chosen as synchronization errors, are employed to approximate the unknown nonlinear functions. Based on the fractional Lyapunov stability criterion, an adaptive fuzzy synchronization controller is designed, and the stability of the closed-loop system, the convergence of the synchronization error, as well as the boundedness of all signals involved can be guaranteed. To update the fuzzy parameters, fractional-order adaptations laws are proposed. Just like the stability analysis in integer-order systems, a quadratic Lyapunov function is used in this paper. Finally, simulation examples are given to show the effectiveness of the proposed method.

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Chaotic system optimal tracking using data-based synchronous method with unknown dynamics and disturbances

宋睿卓, 魏庆来

2017 (3): 30505-030505. doi: 10.1088/1674-1056/26/3/030505

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We develop an optimal tracking control method for chaotic system with unknown dynamics and disturbances. The method allows the optimal cost function and the corresponding tracking control to update synchronously. According to the tracking error and the reference dynamics, the augmented system is constructed. Then the optimal tracking control problem is defined. The policy iteration (PI) is introduced to solve the min-max optimization problem. The off-policy adaptive dynamic programming (ADP) algorithm is then proposed to find the solution of the tracking Hamilton-Jacobi-Isaacs (HJI) equation online only using measured data and without any knowledge about the system dynamics. Critic neural network (CNN), action neural network (ANN), and disturbance neural network (DNN) are used to approximate the cost function, control, and disturbance. The weights of these networks compose the augmented weight matrix, and the uniformly ultimately bounded (UUB) of which is proven. The convergence of the tracking error system is also proven. Two examples are given to show the effectiveness of the proposed synchronous solution method for the chaotic system tracking problem.

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Moderate point: Balanced entropy and enthalpy contributions in soft matter

贺宝记, 王延颋

2017 (3): 30506-030506. doi: 10.1088/1674-1056/26/3/030506

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Various soft materials share some common features, such as significant entropic effect, large fluctuations, sensitivity to thermodynamic conditions, and mesoscopic characteristic spatial and temporal scales. However, no quantitative definitions have yet been provided for soft matter, and the intrinsic mechanisms leading to their common features are unclear. In this work, from the viewpoint of statistical mechanics, we show that soft matter works in the vicinity of a specific thermodynamic state named moderate point, at which entropy and enthalpy contributions among substates along a certain order parameter are well balanced or have a minimal difference. Around the moderate point, the order parameter fluctuation, the associated response function, and the spatial correlation length maximize, which explains the large fluctuation, the sensitivity to thermodynamic conditions, and mesoscopic spatial and temporal scales of soft matter, respectively. Possible applications to switching chemical bonds or allosteric biomachines determining their best working temperatures are also briefly discussed.

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Spin dynamics of magnetic resonance with parametric modulation in a potassium vapor cell

张锐, 汪之国, 彭翔, 黎文浩, 李松健, 郭弘

2017 (3): 30701-030701. doi: 10.1088/1674-1056/26/3/030701

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A typical magnetic-resonance scheme employs a static bias magnetic field and an orthogonal driving magnetic field oscillating at the Larmor frequency, at which the atomic polarization precesses around the static magnetic field. Here we demonstrate both theoretically and experimentally the variations of the resonance condition and the spin precession dynamics resulting from the parametric modulation of the bias field. We show that the driving magnetic field with the frequency detuned by different harmonics of the parametric modulation frequency can lead to resonance as well. Also, a series of frequency sidebands centered at the driving frequency and spaced by the parametric modulation frequency can be observed in the precession of the atomic polarization. We further show that the resonant amplitudes of the sidebands can be controlled by varying the ratio between the amplitude and the frequency of the parametric modulation. These effects could be used in different atomic magnetometry applications.

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Potential energy curves, transition dipole moments, and radiative lifetimes of KBe molecule

万明杰, 金成国, 虞游, 黄多辉, 邵菊香

2017 (3): 33101-033101. doi: 10.1088/1674-1056/26/3/033101

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An ab initio calculations on the ground and low-lying excited states (X²Σ⁺, 2²Σ⁺, 3²Σ⁺, 1⁴Π, 2⁴Π, 1⁴Σ⁺, 2⁴Σ⁺, and 3⁴Σ⁺) of KBe molecule have been performed using multireference configuration interaction (MRCI) plus Davidson corrections (MRCI+Q) approach with all electron basis set aug-cc-pCV5Z-DK for Be and def2-AQZVPP-JKFI for K. The 3²Σ⁺, 1⁴Π, 2⁴Π, 1⁴Σ⁺, 2⁴Σ⁺, and 3⁴Σ⁺ states are investigated for the first time. Inner shell electron correlations are computed on the potential energy curves (PECs) calculations. The spectroscopic and molecular parameters are also predicted. In addition, The transition properties including transition dipole moment, Franck-Condon factors q_v'v'', Einstein coefficients A_v'v'', and the radiative lifetimes τ_v' for the 2²Σ⁺-X²Σ⁺, 3²Σ⁺-X²Σ⁺, and 2⁴Π-1⁴Π transitions are predicted at the same time.

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Comparative study of Mo₂Ga₂C with superconducting MAX phase Mo₂GaC: First-principles calculations

M A Ali,M R Khatun,N Jahan,M M Hossain

2017 (3): 33102-033102. doi: 10.1088/1674-1056/26/3/033102

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The structural, electronic, optical and thermodynamic properties of Mo₂Ga₂C are investigated using density functional theory (DFT) within the generalized gradient approximation (GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states (DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters (e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) are calculated for the first time. The study of dielectric constant (ε₁) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo₂Ga₂C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of T_c expression using available parameter values (DOS, Debye temperature, atomic mass, etc.) suggests that the compound is less likely to be superconductor.

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Molecular dynamics simulations of the effects of sodium dodecyl sulfate on lipid bilayer

徐斌, 林文强, 汪小刚, 曾松伟, 周国泉, 陈均朗

2017 (3): 33103-033103. doi: 10.1088/1674-1056/26/3/033103

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Molecular dynamics simulations have been performed on the fully hydrated lipid bilayer with different concentrations of sodium dodecyl sulfate (SDS). SDS can readily penetrate into the membrane. The insertion of SDS causes a decrease in the bilayer area and increases in the bilayer thickness and lipid tail order, when the fraction of SDS is less than 28%. Through calculating the binding energy, we confirm that the presence of SDS strengthens the interactions among the DPPC lipids, while SDS molecules act as intermedia. Both the strong hydrophilic interactions between sulfate and phosphocholine groups and the hydrophobic interactions between SDS and DPPC hydrocarbon chains contribute to the tight packing and ordered alignment of the lipids. These results are in good agreement with the experimental observations and provide atomic level information that complements the experiments.

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Atomic crystals resistive switching memory

刘春森, 张卫, 周鹏

2017 (3): 33201-033201. doi: 10.1088/1674-1056/26/3/033201

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Facing the growing data storage and computing demands, a high accessing speed memory with low power and non-volatile character is urgently needed. Resistive access random memory with 4F² cell size, switching in sub-nanosecond, cycling endurances of over 10¹² cycles, and information retention exceeding 10 years, is considered as promising next-generation non-volatile memory. However, the energy per bit is still too high to compete against static random access memory and dynamic random access memory. The sneak leakage path and metal film sheet resistance issues hinder the further scaling down. The variation of resistance between different devices and even various cycles in the same device, hold resistive access random memory back from commercialization. The emerging of atomic crystals, possessing fine interface without dangling bonds in low dimension, can provide atomic level solutions for the obsessional issues. Moreover, the unique properties of atomic crystals also enable new type resistive switching memories, which provide a brand-new direction for the resistive access random memory.

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Positronium formation for positron scattering from metastable hydrogen

林蔺, 汪宏年, 焦利光

2017 (3): 33401-033401. doi: 10.1088/1674-1056/26/3/033401

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Positronium (Ps) formation for positron impact on metastable hydrogen in 2s state has been studied by using the two-channel, two-center eikonal final state-continuum initial distorted wave (EFS-CDW) method. The differential, integrated, and total cross sections for Ps formation in different states have been calculated from each channel opening thresholds to high energy region. The results are compared with other theoretical calculations available in the literature. For Ps formation in s-state at intermediate and high energies, our results are in good agreement with the prediction of distorted wave theory. Those formed in p-states and the total Ps formation cross sections are reported for the first time. It is shown that the total Ps formation cross sections for positron scattering from H(2s) state are significantly larger at relatively low energies, while smaller at high energies, compared with those obtained from hydrogen in ground state.

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Direct loading of atoms from a macroscopic quadrupole magnetic trap into a microchip trap

程俊, 张敬芳, 许忻平, 张海潮, 王育竹

2017 (3): 33701-033701. doi: 10.1088/1674-1056/26/3/033701

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We demonstrate the direct loading of cold atoms into a microchip 2-mm Z-trap, where the evaporative cooling can be performed efficiently, from a macroscopic quadrupole magnetic trap with a high loading efficiency. The macroscopic quadrupole magnetic trap potential is designed to be moveable by controlling the currents of the two pairs of anti-Helmholtz coils. The cold atoms are initially prepared in a standard six-beam magneto-optical trap and loaded into the macroscopic quadrupole magnetic trap, and then transported to the atom chip surface by moving the macroscopic trap potential. By means of a three-dimensional absorption imaging system, we are able to optimize the position alignment of the atom cloud in the macroscopic trap and the microchip Z-shaped wire. Consequently, with a proper magnetic transfer scheme, we load the cold atoms into the microchip Z-trap directly and efficiently. The loading efficiency is measured to be about 50%. This approach can be used to generate appropriate ultracold atoms sources, for example, for a magnetically guided atom interferometer based on atom chip.

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BaF radical: A promising candidate for laser cooling and magneto-optical trapping

许亮, 魏斌, 夏勇, 邓联忠, 印建平

2017 (3): 33702-033702. doi: 10.1088/1674-1056/26/3/033702

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Recently, there have been great interest and advancement in the field of laser cooling and magneto-optical trapping of molecules. The rich internal structure of molecules naturally lends themselves to extensive and exciting applications. In this paper, the radical ¹³⁸Ba¹⁹F, as a promising candidate for laser cooling and magneto-optical trapping, is discussed in detail. The highly diagonal Franck-Condon factors between the X²Σ_1/2⁺ and A²Π_1/2 states are first confirmed with three different methods. Afterwards, with the effective Hamiltonian approach and irreducible tensor theory, the hyperfine structure of the X²Σ_1/2⁺ state is calculated accurately. A scheme for laser cooling is given clearly. Besides, the Zeeman effects of the upper (A²Π_1/2) and lower (X²Σ_1/2⁺) levels are also studied, and their respective g factors are obtained under a weak magnetic field. Its large g factor of the upper state A²Π_1/2 is advantageous for magneto-optical trapping. Finally, by studying Stark effect of BaF in the X²Σ_1/2⁺, we investigate the dependence of the internal effective electric field on the applied electric field. It is suggested that such a laser-cooled BaF is also a promising candidate for precision measurement of electron electric dipole moment.

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Optical properties of phosphorene

卢曰瑞

2017 (3): 34201-034201. doi: 10.1088/1674-1056/26/3/034201

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Phosphorene is a two-dimensional semiconductor with layers-dependent bandgap in the near-infrared range and it has attracted a great deal of attention due to its high anisotropy and carrier mobility. The highly anisotropic nature of phosphorene has been demonstrated through Raman and polarization photoluminescence measurements. Photoluminescence spectroscopy has also revealed the layers-dependent bandgap of phosphorene. Furthermore, due to the reduced dimensionality and screening in phosphorene, excitons and trions can stably exist at elevated temperatures and have large binding energies. The exciton and trion dynamics are thus detected by applying electrical bias or optical injection to the phosphorene system. Finally, various optical and optoelectronic applications based on phosphorene have been demonstrated and discussed.

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Two-dimensional materials for ultrafast lasers

王枫秋

2017 (3): 34202-034202. doi: 10.1088/1674-1056/26/3/034202

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As the fundamental optical properties and novel photophysics of graphene and related two-dimensional (2D) crystals are being extensively investigated and revealed, a range of potential applications in optical and optoelectronic devices have been proposed and demonstrated. Of the many possibilities, the use of 2D materials as broadband, cost-effective and versatile ultrafast optical switches (or saturable absorbers) for short-pulsed lasers constitutes a rapidly developing field with not only a good number of publications, but also a promising prospect for commercial exploitation. This review primarily focuses on the recent development of pulsed lasers based on several representative 2D materials. The comparative advantages of these materials are discussed, and challenges to practical exploitation, which represent good future directions of research, are laid out.

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Graphene integrated photodetectors and opto-electronic devices–a review

王肖沐, 甘雪涛

2017 (3): 34203-034203. doi: 10.1088/1674-1056/26/3/034203

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Graphene and other two-dimensional materials have recently emerged as promising candidates for next-generation, high-performance photonics. In this paper, the progress of research into photodetectors and other electro-optical devices based on graphene integrated silicon photonics is briefly reviewed. We discuss the performance metrics, photo-response mechanisms, and experimental results of the latest graphene photodetectors integrated with silicon photonics. We also lay out the unavoidable performance trade-offs in meeting the requirements of various applications. In addition, we describe other opto-electronic devices based on this idea. Integrating two-dimensional materials with a silicon platform provides new opportunities in advanced integrated photonics.

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Reflection and transmission of Laguerre Gaussian beam from uniaxial anisotropic multilayered media

李海英, 吴振森, 尚庆超, 白璐, 李正军

2017 (3): 34204-034204. doi: 10.1088/1674-1056/26/3/034204

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Based on angular spectrum expansion and 4×4 matrix theory, the reflection and transmission characteristics of a Laguerre Gaussian (LG) beam from uniaxial anisotropic multilayered media are studied. The reflected and transmitted beam fields of an LG beam are derived. In the case where the principal coordinates of the uniaxial anisotropic media coincide with the global coordinates, the reflected and transmitted beam intensities from a uniaxial anisotropic slab and three-layered media are numerically simulated. It is shown that the reflected intensity components of the incident beam, especially the TM polarized incident beam, are smaller than the transmitted intensity components. The distortion of the reflected intensity component is more evident than that of the transmitted intensity component. The distortion of intensity distribution is greatly affected by the dielectric tensor and the thickness of anisotropic media. We finally extend the application of the method to general anisotropic multilayered media.

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Fiber core mode leakage induced by refractive index variation in high-power fiber laser

闫平, 王雪娇, 黄昱升, 付晨, 孙骏逸, 肖起榕, 李丹, 巩马理

2017 (3): 34205-034205. doi: 10.1088/1674-1056/26/3/034205

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This paper presents an investigation of specific optical fiber core mode leakage behavior that occurs in high-power double-clad fiber lasers as a result of thermally-induced refractive index variations. A model of the power transfer between the core modes and the cladding modes during thermally-induced refractive index variations is established based on the mode coupling theory. The results of numerical simulations based on actual laser parameters are presented. Experimental measurements were also carried out, the results showed good agreement with the corresponding simulation results.

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Spatial chirp in Ti:sapphire multipass amplifier

黎文开, 陆俊, 李妍妍, 郭晓杨, 吴分翔, 於林鹏, 王朋飞, 许毅, 冷雨欣

2017 (3): 34206-034206. doi: 10.1088/1674-1056/26/3/034206

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The spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the one-dimensional (1D) and two-dimensional (2D) Frantz-Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti:sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti:sapphire chirped pulse amplifier system.

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Visible and near-infrared optical properties of Nd: CLNGG crystal waveguides formed by proton implantation

刘春晓, 沈晓亮, 李玮楠, 韦玮

2017 (3): 34207-034207. doi: 10.1088/1674-1056/26/3/034207

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A Nd:CLNGG waveguide structure operated at wavelengths of both 632.8 nm and 1539 nm was demonstrated for the first time to our knowledge, which was produced by the 480-keV H⁺ ion implantation with a dose of 1.0×10¹⁷ protons/cm². Its propagating modes at 632.8 nm and 1539 nm were measured by the well-known prism coupling technique. The refractive index profile at either 632.8-nm wavelength or 1539-nm wavelength was optical barrier type in the proton-implanted Nd:CLNGG crystal optical waveguide, which was calculated by using the reflectivity calculation method. The near-field light intensity distributions were also simulated by the finite-difference beam propagation method in the visible and near-infrared bands.

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Band gap engineering of atomically thin two-dimensional semiconductors

葛翠环, 李洪来, 朱小莉, 潘安练

2017 (3): 34208-034208. doi: 10.1088/1674-1056/26/3/034208

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Atomically thin two-dimensional (2D) layered materials have potential applications in nanoelectronics, nanophotonics, and integrated optoelectronics. Band gap engineering of these 2D semiconductors is critical for their broad applications in high-performance integrated devices, such as broad-band photodetectors, multi-color light emitting diodes (LEDs), and high-efficiency photovoltaic devices. In this review, we will summarize the recent progress on the controlled growth of composition modulated atomically thin 2D semiconductor alloys with band gaps tuned in a wide range, as well as their induced applications in broadly tunable optoelectronic components. The band gap engineered 2D semiconductors could open up an exciting opportunity for probing their fundamental physical properties in 2D systems and may find diverse applications in functional electronic/optoelectronic devices.

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Thermal properties of two-dimensional materials

张刚, 张永伟

2017 (3): 34401-034401. doi: 10.1088/1674-1056/26/3/034401

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Two-dimensional (2D) materials, such as graphene, phosphorene, and transition metal dichalcogenides (e.g., MoS₂ and WS₂), have attracted a great deal of attention recently due to their extraordinary structural, mechanical, and physical properties. In particular, 2D materials have shown great potential for thermal management and thermoelectric energy generation. In this article, we review the recent advances in the study of thermal properties of 2D materials. We first review some important aspects in thermal conductivity of graphene and discuss the possibility to enhance the ultra-high thermal conductivity of graphene. Next, we discuss thermal conductivity of MoS₂ and the new strategy for thermal management of MoS₂ device. Subsequently, we discuss the anisotropic thermal properties of phosphorene. Finally, we review the application of 2D materials in thermal devices, including thermal rectifier and thermal modulator.

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Numerical study on the gas heating mechanism in pulse-modulated radio-frequency glow discharge

王奇, 于晓丽, 王德真

2017 (3): 35201-035201. doi: 10.1088/1674-1056/26/3/035201

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The gas heating mechanism in the pulse-modulated radio-frequency (rf) discharge at atmospheric pressure was investigated with a one-dimensional two-temperature fluid model. Firstly, the spatiotemporal profiles of the gas temperature (T_g) in both consistent rf discharge and pulse-modulated rf discharge were compared. The results indicated that T_g decreases considerably with the pulse-modulated power, and the elastic collision mechanism plays a more important role in the gas heating change. Secondly, the influences of the duty cycle on the discharge parameters, especially on the T_g, were studied. It was found that T_g decreases almost linearly with the reduction of the duty cycle, and there exists one ideal value of the duty cycle, by which both the T_g can be adjusted and the glow mode can be sustained. Thirdly, the discharge mode changing from α to γ mode in the pulse-modulated rf discharge was investigated, the spatial distributions of T_g in the two modes show different features and the ion Joule heating is more important during the mode transition.

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Dense pair plasma generation by two laser pulses colliding in a cylinder channel

刘建勋, 马燕云, 余同普, 赵军, 杨晓虎, 邹德滨, 张国博, 赵媛, 杨靖康, 李汉臻, 卓红斌, 邵福球

2017 (3): 35202-035202. doi: 10.1088/1674-1056/26/3/035202

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An all-optical scheme for high-density pair plasmas generation is proposed by two laser pulses colliding in a cylinder channel. Two dimensional particle-in-cell simulations show that, when the first laser pulse propagates in the cylinder, electrons are extracted out of the cylinder inner wall and accelerated to high energies. These energetic electrons later run into the second counter-propagating laser pulse, radiating a large amount of high-energy gamma photons via the Compton back-scattering process. The emitted gamma photons then collide with the second laser pulse to initiate the Breit-Wheeler process for pairs production. Due to the strong self-generated fields in the cylinder, positrons are confined in the channel to form dense pair plasmas. Totally, the maximum density of pair plasmas can be 4.60×10²⁷ m^-3, for lasers with an intensity of 4×10²² W·cm^-2. Both the positron yield and density are tunable by changing the cylinder radius and the laser parameters. The generated dense pair plasmas can further facilitate investigations related to astrophysics and particle physics.

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Solid-like ablation propulsion generation in nanosecond pulsed laser interaction with carbon-doped glycerol

郑志远, 张思齐, 梁田, 齐婧, 汤唯冲, 肖珂, 高禄, 高华, 张自力

2017 (3): 35203-035203. doi: 10.1088/1674-1056/26/3/035203

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A solid-like propellant of carbon-doped glycerol ablated by a nanosecond pulsed laser is investigated. The results show that the specific impulse increases with increasing carbon content, and a maximum value of 228 s is obtained. The high specific impulse is attributed to the low ablated mass loss that occurs at high carbon content. More importantly, with increasing carbon content, the properties of the doped glycerol approach to those of a solid. These results indicate that propulsion at the required coupling coefficient and specific impulse can be realized by doping a liquid propellant with an absorber.

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Intrinsic luminescence centers in γ- and θ-alumina nanoparticles

Abdolvahab Amirsalari,Saber Farjami Shayesteh,Reza Taheri Ghahrizjani

2017 (3): 36101-036101. doi: 10.1088/1674-1056/26/3/036101

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In this study, we investigate the photoluminescence (PL) properties of γ and θ-alumina nanoparticles synthesized by the chemical wet method followed by annealing. The obtained experimental results indicate the presence of some favorable near ultraviolet (NUV)-orange luminescent centers for usage in various luminescence applications, such as oxygen vacancies (F, F₂⁺, F₂²⁺, and F₂ centers), OH related defects, cation interstitial centers, and some new luminescence bands attributed to trapped-hole centers or donor-acceptor centers. The energy states of each defect are discussed in detail. The defects mentioned could alter the electronic structure by producing some energy states in the band gap that result in the optical absorption in the middle ultraviolet (MUV) region. Spectra show that photoionazation of F and F₂ centers plays a crucial role in providing either free electrons for the conduction band, or the photoconversions of aggregated oxygen vacancies into each other, or mobile electrons for electrons-holes recombination process by the Shockley-Read-Hall (SRH) mechanism.

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First-principles investigation on N/C co-doped CeO₂

任荣康, 张明举, 彭健, 牛猛, 李健宁, 郑树凯

2017 (3): 36102-036102. doi: 10.1088/1674-1056/26/3/036102

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The N and C doping effects on the crystal structures, electronic and optical properties of fluorite structure CeO₂ have been investigated using the first-principles calculation. Co-doping these two elements results in the local lattice distortion and volume expansion of CeO₂. Compared with the energy band structure of pure CeO₂, some local energy levels appear in the forbidden band, which may facilitate the light absorption. Moreover, the enhanced photo-catalytic properties of CeO₂ were explained through the absorption spectra and the selection rule of the band-to-band transitions.

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Total ionizing dose induced single transistor latchup in 130-nm PDSOI input/output NMOSFETs

樊双, 胡志远, 张正选, 宁冰旭, 毕大炜, 戴丽华, 张梦映, 张乐情

2017 (3): 36103-036103. doi: 10.1088/1674-1056/26/3/036103

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Total ionizing dose induced single transistor latchup effects for 130 nm partially depleted silicon-on-insulator (PDSOI) NMOSFETs with the bodies floating were studied in this work. The latchup phenomenon strongly correlates with the bias configuration during irradiation. It is found that the high body doping concentration can make the devices less sensitive to the single transistor latchup effect, and the onset drain voltage at which latchup occurs can degrade as the total dose level rises. The mechanism of band-to-band tunneling (BBT) has been discussed. Two-dimensional simulations were conducted to evaluate the BBT effect. It is demonstrated that BBT combined with the positive trapped charge in the buried oxide (BOX) contributes a lot to the latchup effect.

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Mechanical and thermodynamical stability of BiVO₄ polymorphs using first-principles study

A K M Farid Ul Islam,Md Nurul Huda Liton,H M Tariqul Islam,Md Al Helal,Md Kamruzzaman

2017 (3): 36301-036301. doi: 10.1088/1674-1056/26/3/036301

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First principles calculations of structural, electronic, mechanical, and thermodynamic properties of different polymorphs of BiVO₄ are performed using Bender-type plane/wave ultrasoft pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT). The calculated structural and electronic properties are consistent with the previous theoretical and experimental results. The electronic structures reveal that m-BiVO₄, op-BiVO₄, and st-BiVO₄ have indirect band gaps, on the other hand, zt-BiVO₄ has a direct band gap. From the DOS and Mulliken's charge analysis, it is observed that only m-BiVO₄ has 6s² Bi lone pair. Bond population analysis indicates that st-BiVO₄ shows a more ionic nature and a similar result is obtained from the elastic properties. From the elastic properties, it is observed that st-BiVO₄ is more mechanically stable than the others. st-BiVO₄ is more ductile and useful for high electro-optical and electro-mechanical coupling devices. Our calculated thermodynamic properties confirm the similar characteristics found from electronic and elastic properties. m-BiVO₄ is useful as photocatalysts, solid state electrolyte, and electrode and other polymorphs are applicable in electronic device fabrications.

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Theoretical description of electron-phonon Fock space for gapless and gapped nanowires

Ashrafalsadat Shariati,Hassan Rabani,Mohammad Mardaani

2017 (3): 36302-036302. doi: 10.1088/1674-1056/26/3/036302

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We study the effect of electron-phonon (e-ph) interaction on the elastic and inelastic electronic transport of a nanowire connected to two simple rigid leads within the tight-binding and harmonic approximations. The model is constructed using Green's function and multi-channel techniques, taking into account the local and nonlocal e-ph interactions. Then, we examine the model for the gapless (simple chain) and gapped (PA-like nanowire) systems. The results show that the tunneling conductance is improved by the e-ph interaction in both local and nonlocal regimes, while for the resonance conductance, the coherent part mainly decreases and the incoherent part increases. At the corresponding energies which depend on the phonon frequency, two dips in the elastic and two peaks in the inelastic conductance spectra appear. The reason is the absorption of the phonon by the electron in transition into inelastic channels.

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Lattice vibration and thermodynamical properties of a single-layergraphene in the presence of vacancy defects

黎莎, 吕增涛

2017 (3): 36303-036303. doi: 10.1088/1674-1056/26/3/036303

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The phonon density of states (PDOS) and the thermodynamical properties including the heat capacity, the free energy, and the entropy of a single-layer graphene with vacancy defects have been studied theoretically. We first analytically derive the general formula of the lattice vibration frequency, and then numerically discuss the effect of the defects on the PDOS. Our results suggest that the vacancy defects will induce the sawtooth-like oscillation of the PDOS and the specific oscillation patterns depend on the concentration and the spatial distribution of the vacancies. In addition, it is verified that the vacancy defects will cause the increase of the heat capacity because of the vacancy-induced low-frequency resonant peak. Moreover, the influences of the vacancies on the free energy and the entropy are investigated.

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Spatial heterogeneity in liquid-liquid phase transition

段云瑞, 李涛, 吴维康, 李洁, 周戌燕, 刘思达, 李辉

2017 (3): 36401-036401. doi: 10.1088/1674-1056/26/3/036401

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Molecular dynamics simulations are performed to investigate the liquid-liquid phase transition (LLPT) and the spatial heterogeneity in Al-Pb monotectic alloys. The results reveal that homogeneous liquid Al-Pb alloy undergoes an LLPT, separating into Al-rich and Pb-rich domains, which is quite different from the isocompositional liquid water with a transition between low-density liquid (LDL) and high-density liquid (HDL). With spatial heterogeneity becoming large, LLPT takes place correspondingly. The relationship between the cooling rate, relaxation temperature and percentage of Al and the spatial heterogeneity is also reported. This study may throw light on the relationship between the structure heterogeneity and LLPT, which provides novel strategies to control the microstructures in the fabrication of the material with high performance.

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Large elastocaloric effect in Ti-Ni shape memory alloy below austenite finish temperature

罗小华, 任卫军, 金伟, 张志东

2017 (3): 36501-036501. doi: 10.1088/1674-1056/26/3/036501

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Solid refrigeration technology based on the elastocaloric effect has a great potential alternative to the conventional vapor compression cooling. Here we report the large elastocaloric effect in Ti-Ni (50 at%) shape memory alloy below its austenite finish temperature A_f under different strain. Both Maxwell's and Clausius-Clapeyron equations are used to estimate the entropy change. The strain-induced entropy change increases with raising the strain and gets a maximum value at a few kelvins below A_f. The maximum entropy changes ΔS_max are -20.44 and -53.70 J/kg·K, respectively for 1% and 2% strain changes. Large entropy change may be obtained down to 20 K below A_f. The temperature of the maximum entropy change remains unchanged before the plastic deformation appears but moves towards low temperature when the plastic deformation happens.

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General equation describing viscosity of metallic melts under horizontal magnetic field

许亦鹏, 赵晓林, 颜廷亮

2017 (3): 36601-036601. doi: 10.1088/1674-1056/26/3/036601

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Viscosities of pure Ga, Ga₈₀Ni₂₀, and Ga₈₀Cr₂₀ metallic melts under a horizontal magnetic field were investigated by a torsional oscillation viscometer. A mathematical physical model was established to quantitatively describe the viscosity of single and binary metallic melts under a horizontal magnetic field. The relationship between the viscosity and the electrical resistivity under the horizontal magnetic field was studied, which can be described as η_B=η+(2H)/(πΩ)B² (η_B is the viscosity under the horizontal magnetic field, η is the viscosity without the magnetic field, H is the height of the sample, Ω is the electrical resistivity, and B is the intensity of magnetic field). The viscosity under the horizontal magnetic field is proportional to the square of the intensity of the magnetic field, which is in very good agreement with the experimental results. In addition, the proportionality coefficient of η_B and quadratic B, which is related to the electrical resistivity, conforms to the law established that increasing the temperature of the completely mixed melts is accompanied by an increase of the electrical resistivity. We can predict the viscosity of metallic melts under magnetic field by measuring the electrical resistivity based on our equation, and vice versa. This discovery is important for understanding condensed-matter physics under external magnetic field.

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Photodetecting and light-emitting devices based on two-dimensional materials

于远方, 缪峰, 何军, 倪振华

2017 (3): 36801-036801. doi: 10.1088/1674-1056/26/3/036801

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Two-dimensional (2D) materials, e.g., graphene, transition metal dichalcogenides (TMDs), and black phosphorus (BP), have demonstrated fascinating electrical and optical characteristics and exhibited great potential in optoelectronic applications. High-performance and multifunctional devices were achieved by employing diverse designs, such as hybrid systems with nanostructured materials, bulk semiconductors and organics, forming 2D heterostructures. In this review, we mainly discuss the recent progress of 2D materials in high-responsive photodetectors, light-emitting devices and single photon emitters. Hybrid systems and van der Waals heterostructure-based devices are emphasized, which exhibit great potential in state-of-the-art applications.

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Light-matter interaction of 2D materials: Physics and device applications

李梓维, 胡义涵, 李瑜, 方哲宇

2017 (3): 36802-036802. doi: 10.1088/1674-1056/26/3/036802

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In the last decade, the rise of two-dimensional (2D) materials has attracted a tremendous amount of interest for the entire field of photonics and opto-electronics. The mechanism of light-matter interaction in 2D materials challenges the knowledge of materials physics, which drives the rapid development of materials synthesis and device applications. 2D materials coupled with plasmonic effects show impressive optical characteristics, involving efficient charge transfer, plasmonic hot electrons doping, enhanced light-emitting, and ultrasensitive photodetection. Here, we briefly review the recent remarkable progress of 2D materials, mainly on graphene and transition metal dichalcogenides, focusing on their tunable optical properties and improved opto-electronic devices with plasmonic effects. The mechanism of plasmon enhanced light-matter interaction in 2D materials is elaborated in detail, and the state-of-the-art of device applications is comprehensively described. In the future, the field of 2D materials holds great promise as an important platform for materials science and opto-electronic engineering, enabling an emerging interdisciplinary research field spanning from clean energy to information technology.

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Geometric stability and electronic structure of infinite and finite phosphorus atomic chains

乔婧思, 周霖蔚, 季威

2017 (3): 36803-036803. doi: 10.1088/1674-1056/26/3/036803

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One-dimensional mono- or few-atomic chains were successfully fabricated in a variety of two-dimensional materials, like graphene, BN, and transition metal dichalcogenides, which exhibit striking transport and mechanical properties. However, atomic chains of black phosphorus (BP), an emerging electronic and optoelectronic material, is yet to be investigated. Here, we comprehensively considered the geometry stability of six categories of infinite BP atomic chains, transitions among them, and their electronic structures. These categories include mono- and dual-atomic linear, armchair, and zigzag chains. Each zigzag chain was found to be the most stable in each category with the same chain width. The mono-atomic zigzag chain was predicted as a Dirac semi-metal. In addition, we proposed prototype structures of suspended and supported finite atomic chains. It was found that the zigzag chain is, again, the most stable form and could be transferred from mono-atomic armchair chains. An orientation dependence was revealed for supported armchair chains that they prefer an angle of roughly 35°-37° perpendicular to the BP edge, corresponding to the [110] direction of the substrate BP sheet. These results may promote successive research on mono- or few-atomic chains of BP and other two-dimensional materials for unveiling their unexplored physical properties.

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A review for compact model of graphene field-effect transistors

卢年端, 汪令飞, 李泠, 刘明

2017 (3): 36804-036804. doi: 10.1088/1674-1056/26/3/036804

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Graphene has attracted enormous interests due to its unique physical, mechanical, and electrical properties. Specially, graphene-based field-effect transistors (FETs) have evolved rapidly and are now considered as an option for conventional silicon devices. As a critical step in the design cycle of modern IC products, compact model refers to the development of models for integrated semiconductor devices for use in circuit simulations. The purpose of this review is to provide a theoretical description of current compact model of graphene field-effect transistors. Special attention is devoted to the charge sheet model, drift-diffusion model, Boltzmann equation, density of states (DOS), and surface-potential-based compact model. Finally, an outlook of this field is briefly discussed.

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Electrical property effect of oxygen vacancies in the heterojunction of LaGaO₃/SrTiO₃

王芙凝, 李吉超, 张鑫淼, 刘汉璋, 刘剑, 王春雷, 赵明磊, 苏文斌, 梅良模

2017 (3): 37101-037101. doi: 10.1088/1674-1056/26/3/037101

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Density functional theory within the local density approximation is used to investigate the effect of the oxygen vacancy on the LaGaO₃/SrTiO₃ (001) heterojunction. It is found that the energy favorable configuration is the oxygen vacancy located at the 3^rd layer of the STO substrate, and the antiferrodistortive distortion is induced by the oxygen vacancy introduced on the SrTiO₃ side. Compared with the heterojunction without introducing oxygen vacancy, the heterojunction with introducing the oxygen vacancy does not change the origin of the two-dimensional electron gas (2DEG), that is, the 2DEG still originates from the d_xy electrons, which are split from the t_2g states of Ti atom at interface; however the oxygen vacancy is not beneficial to the confinement of the 2DEG. The extra electrons caused by the oxygen vacancy dominantly occupy the 3d_x²-y² orbitals of the Ti atom nearest to the oxygen vacancy, thus the density of carrier is enhanced by one order of magnitude due to the introduction of oxygen vacancy compared with the density of the ideal structure heterojunction.

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Stability, electronic structures, and mechanical properties of Fe-Mn-Al system from first-principles calculations

刘亚会, 种晓宇, 蒋业华, 冯晶

2017 (3): 37102-037102. doi: 10.1088/1674-1056/26/3/037102

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The stability, electronic structures, and mechanical properties of the Fe-Mn-Al system were determined by first-principles calculations. The formation enthalpy and cohesive energy of these Fe-Mn-Al alloys are negative and show that the alloys are thermodynamically stable. Fe₃Al, with the lowest formation enthalpy, is the most stable compound in the Fe-Mn-Al system. The partial density of states, total density of states, and electron density distribution maps of the Fe-Mn-Al alloys were analyzed. The bonding characteristics of these Fe-Mn-Al alloys are mainly combinations of covalent bonding and metallic bonds. The stress-strain method and Voigt-Reuss-Hill approximation were used to calculate the elastic constants and moduli, respectively. Fe_2.5Mn_0.5Al has the highest bulk modulus, 234.5 GPa. Fe_1.5Mn_1.5Al has the highest shear modulus and Young's modulus, with values of 98.8 GPa and 259.2 GPa, respectively. These Fe-Mn-Al alloys display disparate anisotropies due to the calculated different shape of the three-dimensional curved surface of the Young's modulus and anisotropic index. Moreover, the anisotropic sound velocities and Debye temperatures of these Fe-Mn-Al alloys were explored.

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New ternary superconducting compound LaRu₂As₂: Physical properties from density functional theory calculations

M A Hadi,M S Ali,S H Naqib,A K M A Islam

2017 (3): 37103-037103. doi: 10.1088/1674-1056/26/3/037103

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In this paper, we perform the density functional theory (DFT)-based calculations by the first-principles pseudopotential method to investigate the physical properties of the newly discovered superconductor LaRu₂As₂ for the first time. The optimized structural parameters are in good agreement with the experimental results. The calculated independent elastic constants ensure the mechanical stability of the compound. The calculated Cauchy pressure, Pugh's ratio as well as Poisson's ratio indicate that LaRu₂As₂ should behave as a ductile material. Due to low Debye temperature, LaRu₂As₂ may be used as a thermal barrier coating (TBC) material. The new compound should exhibit metallic nature as its valence bands overlap considerably with the conduction bands. LaRu₂As₂ is expected to be a soft material and easily machinable because of its low hardness value of 6.8 GPa. The multi-band nature is observed in the calculated Fermi surface. A highly anisotropic combination of ionic, covalent and metallic interactions is expected to be in accordance with charge density calculation.

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Passivation effects of phosphorus on 4H-SiC (0001) Si dangling bonds: A first-principles study

李文波, 李玲, 王方方, 郑柳, 夏经华, 秦福文, 王晓琳, 李永平, 刘瑞, 王德君, 潘艳, 杨霏

2017 (3): 37104-037104. doi: 10.1088/1674-1056/26/3/037104

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The effect of phosphorus passivation on 4H-SiC(0001) silicon (Si) dangling bonds is investigated using ab initio atomistic thermodynamic calculations. Phosphorus passivation commences with chemisorption of phosphorus atoms at high-symmetry coordinated sites. To determine the most stable structure during the passivation process of phosphorus, a surface phase diagram of phosphorus adsorption on SiC (0001) surface is constructed over a coverage range of 1/9-1 monolayer (ML). The calculated results indicate that the 1/3 ML configuration is most energetically favorable in a reasonable environment. At this coverage, the total electron density of states demonstrates that phosphorus may effectively reduce the interface state density near the conduction band by removing 4H-SiC (0001) Si dangling bonds. It provides an atomic level insight into how phosphorus is able to reduce the near interface traps.

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Vibration-assisted coherent excitation energy transfer in a detuned dimer

王信, 陈浩, 李晨宇, 李宏荣

2017 (3): 37105-037105. doi: 10.1088/1674-1056/26/3/037105

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The important role of high-energy intramolecular vibrational modes for excitation energy transfer in the detuned photosynthetic systems is studied. Based on a basic dimer model which consists of two two-level systems (pigments) coupled to high-energy vibrational modes, we find that the high-energy intramolecular vibrational modes can enhance the energy transfer with new coherent transfer channels being opened when the phonon energy matches the detuning between the two pigments. As a result, the energy can be effectively transferred into the acceptor. The effective Hamiltonian is obtained to reveal the strong coherent energy exchange among the donor, the acceptor, and the high-energy intramolecular. A semi-classical explanation of the phonon-assisted mechanism is also shown.

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Recent progress on integrating two-dimensional materials with ferroelectrics for memory devices and photodetectors

王建禄, 胡伟达

2017 (3): 37106-037106. doi: 10.1088/1674-1056/26/3/037106

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Two-dimensional (2D) materials, such as graphene and MoS₂ related transition metal dichalcogenides (TMDC), have attracted much attention for their potential applications. Ferroelectrics, one of the special and traditional dielectric materials, possess a spontaneous electric polarization that can be reversed by the application of an external electric field. In recent years, a new type of device, combining 2D materials with ferroelectrics, has been fabricated. Many novel devices have been fabricated, such as low power consumption memory devices, highly sensitive photo-transistors, etc. using this technique of hybrid systems incorporating ferroelectrics and 2D materials. This paper reviews two types of devices based on field effect transistor (FET) structures with ferroelectric gate dielectric construction (termed FeFET). One type of device is for logic applications, such as a graphene and TMDC FeFET for fabricating memory units. Another device is for optoelectric applications, such as high performance phototransistors using a graphene p-n junction. Finally, we discuss the prospects for future applications of 2D material FeFET.

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Plasma-assisted surface treatment for low-temperature annealed ohmic contact on AlGaN/GaN heterostructure field-effect transistors

王磊, 张家琦, 李柳暗, 前田裕太郎, 敖金平

2017 (3): 37201-037201. doi: 10.1088/1674-1056/26/3/037201

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In this study, a low-temperature annealed ohmic contact process was proposed on AlGaN/GaN heterostructure field effect transistors (HFETs) with the assistance of inductively coupled plasma (ICP) surface treatment. The effect of ICP treatment process on the 2DEG channel as well as the formation mechanism of the low annealing temperature ohmic contact was investigated. An appropriate residual AlGaN thickness and a plasma-induced damage are considered to contribute to the low-temperature annealed ohmic contact. By using a single Al layer to replace the conventional Ti/Al stacks, ohmic contact with a contact resistance of 0.35 Ω·mm was obtained when annealed at 575℃ for 3 min. Good ohmic contact was also obtained by annealing at 500℃ for 20 min.

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Topological transport in Dirac electronic systems: A concise review

宋化鼎, 盛典, 王安琦, 李金光, 俞大鹏, 廖志敏

2017 (3): 37301-037301. doi: 10.1088/1674-1056/26/3/037301

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Various novel physical properties have emerged in Dirac electronic systems, especially the topological characters protected by symmetry. Current studies on these systems have been greatly promoted by the intuitive concepts of Berry phase and Berry curvature, which provide precise definitions of the topological phases. In this topical review, transport properties of topological insulator (Bi₂Se₃), topological Dirac semimetal (Cd₃As₂), and topological insulator-graphene heterojunction are presented and discussed. Perspectives about transport properties of two-dimensional topological nontrivial systems, including topological edge transport, topological valley transport, and topological Weyl semimetals, are provided.

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Band structure of silicon and germanium thin films based on first principles

吴学科, 黄伟其, 黄忠梅, 秦朝建, 董泰阁, 王刚, 唐延林

2017 (3): 37302-037302. doi: 10.1088/1674-1056/26/3/037302

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In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic devices. First principles calculation based on density functional theory (DFT) with the generalized gradient approximation (GGA) are carried out to investigate the energy band gap structure on silicon (Si) and germanium (Ge) nanofilms. Simulation results show that the band gaps in Si (100) and Ge (111) nanofilms become the direct-gap structure in the thickness range less than 7.64 nm and 7.25 nm respectively, but the band gaps of Si (111) and Ge (110) nanofilms still keep in an indirect-gap structure and are independent on film thickness, and the band gaps of Si (110) and Ge (100) nanofilms could be transferred into the direct-gap structure in nanofilms with smaller thickness. It is amazing that the band gaps of Si^(1-x)/2Ge^xSi^(1-x)/2 sandwich structure become the direct-gap structure in a certain area whether (111) or (100) surface. The band structure change of Si and Ge thin films in three orientations is not the same and the physical mechanism is very interesting, where the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects.

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Plasmonic microcavity formed by the Möbius strip

曾扬, 王智勇, 吴远, 陆兰松, 王云祥, 史双瑾, 邱琪

2017 (3): 37303-037303. doi: 10.1088/1674-1056/26/3/037303

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We propose a Möbius-strip-type plasmonic cavity with a silver Möbius strip sandwiched between dielectric layers. By brief theoretical and simulation analyses, we obtain that the Q factor of the cavity remains about 40 and the mode volume is ultrasmall (less than 1 μm³) which is more compact than that of the cylindric cavity. This Möbius-strip-type plasmonic cavity supporting the propagation of surface plasmon polaritons owns some unusual properties such as more effective volume and the spatial separation. More potential applications based on this cavity remain to be explored in future nanophotonics.

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Photon-mediated spin-polarized current in a quantum dot under thermal bias

迟锋, 刘黎明, 孙连亮

2017 (3): 37304-037304. doi: 10.1088/1674-1056/26/3/037304

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Spin-polarized current generated by thermal bias across a system composed of a quantum dot (QD) connected to metallic leads is studied in the presence of magnetic and photon fields. The current of a certain spin orientation vanishes when the dot level is aligned to the lead's chemical potential, resulting in a 100% spin-polarized current. The spin-resolved current also changes its sign at the two sides of the zero points. By tuning the system's parameters, spin-up and spin-down currents with equal strength may flow in opposite directions, which induces a pure spin current without the accompany of charge current. With the help of the thermal bias, both the strength and the direction of the spin-polarized current can be manipulated by tuning either the frequency or the intensity of the photon field, which is beyond the reach of the usual electric bias voltage.

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Transparent conducting indium-tin-oxide (ITO) film as full front electrode in III-V compound solar cell

代盼, 卢建娅, 谭明, 王青松, 吴渊渊, 季莲, 边历峰, 陆书龙, 杨辉

2017 (3): 37305-037305. doi: 10.1088/1674-1056/26/3/037305

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The application of transparent conducting indium-tin-oxide (ITO) film as full front electrode replacing the conventional bus-bar metal electrode in III-V compound GaInP solar cell was proposed. A high-quality, non-rectifying contact between ITO and 10 nm N⁺-GaAs contact layer was formed, which is benefiting from a high carrier concentration of the terrilium-doped N⁺-GaAs layer, up to 2×10¹⁹ cm^-3. A good device performance of the GaInP solar cell with the ITO electrode was observed. This result indicates a great potential of transparent conducting films in the future fabrication of larger area flexible III-V solar cell.

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Broadband microwave frequency doubler based on left-handed nonlinear transmission lines

黄杰, 顾雯雯, 赵倩

2017 (3): 37306-037306. doi: 10.1088/1674-1056/26/3/037306

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A bandwidth microwave second harmonic generator is successfully designed using composite right/left-handed nonlinear transmission lines (CRLH NLTLs) in a GaAs monolithic microwave integrated circuit (MMIC) technology. The structure parameters of CRLH NLTLs, e.g. host transmission line, rectangular spiral inductor, and nonlinear capacitor, have a great impact on the second harmonic performance enhancement in terms of second harmonic frequency, output power, and conversion efficiency. It has been experimentally demonstrated that the second harmonic frequency is determined by the anomalous dispersion of CRLH NLTLs and can be significantly improved by effectively adjusting these structure parameters. A good agreement between the measured and simulated second harmonic performances of Ka-band CRLH NLTLs frequency multipliers is successfully achieved, which further validates the design approach of frequency multipliers on CRLH NLTLs and indicates the potentials of CRLH NLTLs in terms of the generation of microwave and millimeter-wave signal source.

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Toward high-performance two-dimensional black phosphorus electronic and optoelectronic devices

李学飞, 熊雄, 吴燕庆

2017 (3): 37307-037307. doi: 10.1088/1674-1056/26/3/037307

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Recently, black phosphorus (BP) has joined the two-dimensional material family as a promising candidate for electronic and photonic applications due to its moderate bandgap, high carrier mobility, and unusual in-plane anisotropy. Here, we review recent progress in BP-based devices, such as field-effect transistors, contact resistance, quantum transport, stability, photodetector, heterostructure, and in-plane anisotropy. We also give our perspectives on future BP research directions.

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Validation of the Wiedemann-Franz law in a granular s-wave superconductor in the nanometer scale

A Yousefvand,H Salehi,M Zargar Shoushtari

2017 (3): 37401-037401. doi: 10.1088/1674-1056/26/3/037401

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The present study tries to evaluate the validity of the Wiedemann-Franz law in a granular s-wave superconductor in the presence of concentrated impurities. By using Green's function method and the Kubo formula technique, three distinct contributions of the Aslamazov-Larkin, the Maki-Thompson and, the density of states are calculated for both the electrical conductivity and the thermal conductivity in a granular s-wave superconductor. It is demonstrated that these different contributions to the fluctuation conductivity depend differently on the tunneling because of their different natures. This study examines the transport in a granular superconductor system in three dimensions in the limit of large tunneling conductance, which makes it possible to ignore all localization effects and the Coulomb interaction. We find that the tunneling is efficient near the critical temperature and that there is a crossover to the characteristic behavior of a homogeneous system. When it is far from the critical temperature, the tunneling is not effective and the system behaves as an ensemble of real zero-dimensional grains. The results show that the Wiedemann-Franz law is violated in both temperature regions.

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Exact solutions of an Ising spin chain with a spin-1 impurity

黄旭初

2017 (3): 37501-037501. doi: 10.1088/1674-1056/26/3/037501

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An exact solution of a single impurity model is hard to derive since it breaks translation invariance symmetry. We present the exact solution of the spin-1/2 transverse Ising chain imbedded by a spin-1 impurity. Using the hole decomposition scheme, we exactly solve the spin-1 impurity in two subspaces which are generated by a conserved hole operator. The impurity enlarges the energy deformation of the ground state above a pure transverse Ising system without impurity. The specific heat coefficient shows a small anomaly at low temperature for finite size. This indicates that the impurity can tune the ground state from a magnetic impurity space to a non-magnetic impurity space, which only exists for spin-1 impurity comparing with spin-1/2 impurity and a pure transverse Ising chain without impurity. These behaviors essentially come from adding impurity freedom, which induces a competition between hole and fermion excitation depending on the coupling strength with its neighbor and the single-ion anisotropy.

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Magnetic properties and magnetocaloric effect of the Cr-based spinel sulfides Co_1-xCu_xCr₂S₄

郑小超, 李西阳, 何伦华, 张绍英, 唐明华, 王芳卫

2017 (3): 37502-037502. doi: 10.1088/1674-1056/26/3/037502

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Crystallographic structure, magnetic properties, and magnetic entropy change of the Cr-based spinel sulfides Co_1-xCu_xCr₂S₄ (x=0-0.8) have been investigated. All these compounds crystallize into the cubic spinel structure, the Cu substitution shrinks linearly the lattice constant at a ratio of 0.0223 Å per Cu atom in the unit cell, and enhances linearly the Curie temperature and the spontaneous magnetization at the rates of 18 K and 0.33 μ_B/f.u. per Cu atom in the unit cell, respectively. All these compounds show a typical behavior of second order magnetic transition, and a room temperature magnetic entropy change of 2.57 J/kg·K is achieved for Co_0.4Cu_0.6Cr₂S₄.

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Modeling of the loading path dependent magnetomechanical behavior of Galfenol alloy

江慧, 朱洁

2017 (3): 37503-037503. doi: 10.1088/1674-1056/26/3/037503

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The magnetomechanical behavior of single-crystal Galfenol alloy was found to be strongly dependent on the loading paths. An energy-based anisotropic domain rotation model, assuming that the interaction between domains can be ignored and the probability of the magnetic moment pointing along a particular direction is related to the free energy along this direction, is used to simulate the magnetostriction versus magnetic field and stress curve and to track the magnetic domain motion trail. The main reason for loading path dependent effect is the rotation/flipping of the magnetic domains under different loading paths. The effect of loading and unloading paths on 90° magnetic domain motion was studied by choosing different loading and unloading state and paths. The results show that prior loading magnetic field can make the 90° magnetic domains flip to the directions of 45° domains because the magnetic field is the driving force to make the domains rotate, and the final loading state and the loading path both have great influence on the motion of 90° magnetic domains.

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Stoney formula for piezoelectric film/elastic substrate system

周旺民, 李望君, 洪圣运, 金杰, 尹姝媛

2017 (3): 37701-037701. doi: 10.1088/1674-1056/26/3/037701

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With the trends in miniaturization, and particularly the introduction of micro- and nano-electro-mechanical system, piezoelectric materials used in microelectronic devices are deposited usually in the form of thin film on elastic substrates. In this work, the bending of a bilayer comprising a piezoelectric film deposited on an elastic substrate, due to the mismatch, is investigated. An analytic formula relating the curvature of the bilayer to the mismatch, the electroelastic constants and the film thickness is obtained, and from this formula, a transverse piezoelectric constant d₃₁ can be estimated. Meanwhile the influence of electromechanical coupling coefficient on the curvature is discussed.

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CuO added Pb_0.92Sr_0.06Ba_0.02(Mg_1/3Nb_2/3)_0.25(Ti_0.53Zr_0.47)_0.75O₃ ceramics sintered with Ag electrodes at 900℃ for multilayer piezoelectric actuator

徐玉青, 汪尧进, 王一平, 杨颖, 袁国亮

2017 (3): 37702-037702. doi: 10.1088/1674-1056/26/3/037702

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CuO added Pb_0.92Sr_0.06Ba_0.02(Mg_1/3Nb_2/3)_0.25(Ti_0.53Zr_0.47)_0.75O₃ ceramics were studied to prepare high-quality multilayer piezoelectric actuators with pure Ag electrodes at 900℃. CuO addition not only reduced the sintering temperature significantly from 1260℃ to 900℃ but also improved the ceramic density to 7.742 g/cm³. The 0.7 wt.% CuO added ceramic sintered at 900℃ shows the remnant polarization (P_r) of 40 μC/cm², 0.28% strain at 40 kV/cm, and the piezoelectric coefficient (d₃₃) of 630 pC/N. This ceramic shows a strong relaxor characteristic with a Curie temperature of 200℃. Furthermore, the 0.7 wt.% CuO added ceramic and pure Ag electrodes were co-fired at 900℃ to prepare a high-quality multilayer piezoelectric actuator with a d₃₃ of over 450 pC/N per ceramic layer.

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Review of ultrafast spectroscopy studies of valley carrier dynamics in two-dimensional semiconducting transition metal dichalcogenides

孙栋, 赖佳伟, 马骏超, 王钦生, 刘晶

2017 (3): 37801-037801. doi: 10.1088/1674-1056/26/3/037801

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The two-dimensional layered transition metal dichalcogenides provide new opportunities in future valley-based information processing and also provide an ideal platform to study excitonic effects. At the center of various device physics toward their possible electronic and optoelectronic applications is understanding the dynamical evolution of various many-particle electronic states, especially exciton which dominates the optoelectronic response of TMDs, under the novel context of valley degree of freedom. Here, we provide a brief review of experimental advances in using helicity-resolved ultrafast spectroscopy, especially ultrafast pump-probe spectroscopy, to study the dynamical evolution of valley-related many-particle electronic states in semiconducting monolayer transitional metal dichalcogenides.

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Cyclic stress induced phase transformation insuper-bainitic microstructure

修文翠, 韩英, 刘澄, 吴化, 刘云旭

2017 (3): 38101-038101. doi: 10.1088/1674-1056/26/3/038101

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The effects of cyclic stress loading on the microstructual evolution and tensile properties of a medium-carbon super-bainitic steel were investigated. Experimental results show that the cyclic stress can induce the carbon gathering in austenite and phase transformation from film-like retained austenite to twin martensite, which will obviously enhance the tensile strength and the product of tensile strength and ductility. The higher the bainitic transformation temperature, the lower the transformation rate of the retained austenite. The amount and thickness of the film-like retained austenite play an important role during the cyclic stress induced phase transformation.

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Dislocation distributions and tilts in Al(Ga)InAs reverse-graded layers grown on misorientated GaAs substrates

何洋, 孙玉润, 赵勇明, 于淑珍, 董建荣

2017 (3): 38102-038102. doi: 10.1088/1674-1056/26/3/038102

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Compositionally undulating step-graded Al(Ga)In_xAs (x=0.05-0.52) buffers with the following InP layer were grown by metal-organic chemical vapor deposition (MOCVD) on (001) GaAs with a 15° miscut. The dislocation distribution and tilts of the epilayers were examined using x-ray rocking curve and (004) reciprocal space maps (RSM) along two orthogonal <110> directions. The results suggested that such reverse-graded layers have different effects on α and β dislocations. A higher dislocation density was observed along the [110] direction and an epilayer tilt of -1.43° was attained in the [1-10] direction when a reverse-graded layer strategy was employed. However, for conventional step-graded samples, the dislocation density is normally higher along the [1-10] direction.

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Controllable preparation of tungsten/tungsten carbide nanowires or nanodots in nanostructured carbon with hollow macroporous core/mesoporous shell

任晓娜, 夏敏, 燕青芝, 葛昌纯

2017 (3): 38103-038103. doi: 10.1088/1674-1056/26/3/038103

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Large scale tungsten nanowires and tungsten nanodots are prepared in a controllable way. The preparation is based on mechanisms of chemical vapor transportation and phase transformation during the reduction of ammonium metatungstate (AMT) in H₂. The AMT is first encapsulated into the hollow core of nanostructured carbon with hollow macroporous core/mesoporous shell (NC-HMC/MS) and forms nanorods, which are the precursors of both tungsten nanowires and tungsten nanodots. Just by controlling H₂ flow rate and heating rate in the reduction process, the AMT nanorods could turn into nanowires (under low rate condition) or nanodots (under high rate condition). Besides, via heat treatment at 1200℃, the as-obtained nano-sized tungsten could convert into W₂C nanorods or WC nanodots respectively. Furthermore, the diameter of the as-obtained tungsten or tungsten carbide is confined within 50 nm by the NC-HMC/MS, and no agglomeration appears in the obtained nanomaterials.

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Carrier transport via V-shaped pits in InGaN/GaN MQW solar cells

刘诗涛, 全知觉, 王立

2017 (3): 38104-038104. doi: 10.1088/1674-1056/26/3/038104

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Carrier transport via the V-shaped pits (V-pits) in InGaN/GaN multiple-quantum-well (MQW) solar cells is numerically investigated. By simulations, it is found that the V-pits can act as effective escape paths for the photo-generated carriers. Due to the thin barrier thickness and low indium composition of the MQW on V-pit sidewall, the carriers entered the sidewall QWs can easily escape and contribute to the photocurrent. This forms a parallel escape route for the carries generated in the flat quantum wells. As the barrier thickness of the flat MQW increases, more carriers would transport via the V-pits. Furthermore, it is found that the V-pits may reduce the recombination losses of carriers due to their screening effect to the dislocations. These discoveries are not only helpful for understanding the carrier transport mechanism in the InGaN/GaN MQW, but also important in design of the structure of solar cells.

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Improving self-assembly quality of colloidal crystal guided by statistical design of experiments

吴以治, 许小亮, 张海明, 刘玲, 李继超, 杨大宝

2017 (3): 38105-038105. doi: 10.1088/1674-1056/26/3/038105

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A versatile and reliable approach is created to fabricate wafer-scale colloidal crystal that consists of a monolayer of hexagonally close-packed polystyrene (PS) spheres. Making wafer-scale colloidal crystal is usually challenging, and it lacks a general theoretical guidance for experimental approaches. To obtain the optimal conditions for self-assembly, a systematic statistical design and analysis method is utilized here, which applies the pick-the-winner rule. This new method combines spin-coating and thermal treatment, and introduces a mixture of glycol and ethanol as a dispersion system to assist self-assembly. By controlling the parameters of self-assembly, we improve the quality of colloidal crystal and reduce the effect of noise on the experiment. To our best knowledge, we are first to pave this path to harvest colloidal crystals. Importantly, a theoretical analysis using an energy landscape base on our process is also developed to provide insights into the PS spheres' self-assembly.

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Diffusion in the aged aluminium film on iron

A Y Galashev,O R Rakhmanova,V A Kovrov,Yu P Zaikov

2017 (3): 38201-038201. doi: 10.1088/1674-1056/26/3/038201

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Metallic coatings of many types can be applied to steel to provide outstanding, long-term corrosion protection. A thin Al film is studied at an Fe substrate by the molecular dynamics method at temperatures ranging from 300 K to 1173 K. Al atoms are found to penetrate the Fe matrix at a temperature of 873 K. The potential energy of the system changes step-like at a temperature of 1173 K. At such temperature mean square atomic displacement significantly changes. The behaviors of the Al and Fe diffusion coefficients are mainly determined by the temperature dependence of the diffusion activation energy.

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Dye-sensitized solar cell module realized photovoltaic and photothermal highly efficient conversion via three-dimensional printing technology

黄启章, 朱艳青, 史继富, 王雷雷, 钟柳文, 徐刚

2017 (3): 38401-038401. doi: 10.1088/1674-1056/26/3/038401

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Three-dimensional (3D) printing technology is employed to improve the photovoltaic and photothermal conversion efficiency of dye-sensitized solar cell (DSC) module. The 3D-printed concentrator is optically designed and improves the photovoltaic efficiency of the DSC module from 5.48% to 7.03%. Additionally, with the 3D-printed microfluidic device serving as water cooling, the temperature of the DSC can be effectively controlled, which is beneficial for keeping a high photovoltaic conversion efficiency for DSC module. Moreover, the 3D-printed microfluidic device can realize photothermal conversion with an instantaneous photothermal efficiency of 42.1%. The integrated device realizes a total photovoltaic and photothermal conversion efficiency of 49% at the optimal working condition.

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Graphene resistive random memory–the promising memory device in next generation

王雪峰, 赵海明, 杨轶, 任天令

2017 (3): 38501-038501. doi: 10.1088/1674-1056/26/3/038501

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Graphene-based resistive random access memory (GRRAM) has grasped researchers' attention due to its merits compared with ordinary RRAM. In this paper, we briefly review different types of GRRAMs. These GRRAMs can be divided into two categories: graphene RRAM and graphene oxide (GO)/reduced graphene oxide (rGO) RRAM. Using graphene as the electrode, GRRAM can own many good characteristics, such as low power consumption, higher density, transparency, SET voltage modulation, high uniformity, and so on. Graphene flakes sandwiched between two dielectric layers can lower the SET voltage and achieve multilevel switching. Moreover, the GRRAM with rGO and GO as the dielectric or electrode can be simply fabricated. Flexible and high performance RRAM and GO film can be modified by adding other materials layer or making a composite with polymer, nanoparticle, and 2D materials to further improve the performance. Above all, GRRAM shows huge potential to become the next generation memory.

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Superjunction nanoscale partially narrow mesa IGBT towards superior performance

喻巧群, 陆江, 刘海南, 罗家俊, 李博, 王立新, 韩郑生

2017 (3): 38502-038502. doi: 10.1088/1674-1056/26/3/038502

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We present a detailed study of a superjunction (SJ) nanoscale partially narrow mesa (PNM) insulated gate bipolar transistor (IGBT) structure. This structure is created by combining the nanoscale PNM structure and the SJ structure together. It demonstrates an ultra-low saturation voltage (V_ce(sat)) and low turn-off loss (E_off) while maintaining other device parameters. Compared with the conventional 1.2 kV trench IGBT, our simulation result shows that the V_ce(sat) of this structure decreases to 0.94 V, which is close to the theoretical limit of 1.2 kV IGBT. Meanwhile, the fall time decreases from 109.7 ns to 12 ns and the E_off is down to only 37% of that of the conventional structure. The superior tradeoff characteristic between V_ce(sat) and E_off is presented owing to the nanometer level mesa width and SJ structure. Moreover, the short circuit degeneration phenomenon in the very narrow mesa structure due to the collector-induced barriers lowering (CIBL) effect is not observed in this structure. Thus, enough short circuit ability can be achieved by using wide, floating P-well technique. Based on these structure advantages, the SJ-PNM-IGBT with nanoscale mesa width indicates a potentially superior overall performance towards the IGBT parameter limit.

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An improved design for AlGaN solar-blind avalanche photodiodes with enhanced avalanche ionization

汤寅, 蔡青, 杨莲红, 董可秀, 陈敦军, 陆海, 张荣, 郑有炓

2017 (3): 38503-038503. doi: 10.1088/1674-1056/26/3/038503

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To enhance the avalanche ionization, we designed a new separate absorption and multiplication AlGaN solar-blind avalanche photodiode (APD) by using a high/low-Al-content AlGaN heterostructure as the multiplication region instead of the conventional AlGaN homogeneous layer. The calculated results show that the designed APD with Al_0.3Ga_0.7N/Al_0.45Ga_0.55N heterostructure multiplication region exhibits a 60% higher gain than the conventional APD and a smaller avalanche breakdown voltage due to the use of the low-Al-content Al_0.3Ga_0.7N which has about a six times higher hole ionization coefficient than the high-Al-content Al_0.45Ga_0.55N. Meanwhile, the designed APD still remains a good solar-blind characteristic by introducing a quarter-wave AlGaN/AlN distributed Bragg reflectors structure at the bottom of the device.

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Photodetectors based on junctions of two-dimensional transition metal dichalcogenides

魏侠, 闫法光, 申超, 吕全山, 王开友

2017 (3): 38504-038504. doi: 10.1088/1674-1056/26/3/038504

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Transition metal dichalcogenides (TMDCs) have gained considerable attention because of their novel properties and great potential applications. The flakes of TMDCs not only have great light absorption from visible to near infrared, but also can be stacked together regardless of lattice mismatch like other two-dimensional (2D) materials. Along with the studies on intrinsic properties of TMDCs, the junctions based on TMDCs become more and more important in applications of photodetection. The junctions have shown many exciting possibilities to fully combine the advantages of TMDCs, other 2D materials, conventional and organic semiconductors together. Early studies have greatly enriched the application of TMDCs in photodetection. In this review, we investigate the efforts in photodetectors based on the junctions of TMDCs and analyze the properties of those photodetectors. Homojunctions based on TMDCs can be made by surface chemical doping, elemental doping and electrostatic gating. Heterojunction formed between TMDCs/2D materials, TMDCs/conventional semiconductors and TMDCs/organic semiconductor also deserve more attentions. We also compare the advantages and disadvantages of different junctions, and then give the prospects for the development of junctions based on TMDCs.

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Thermal properties of a two-dimensional intrinsically curved semiflexible biopolymer

周子聪, 王延颋

2017 (3): 38701-038701. doi: 10.1088/1674-1056/26/3/038701

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We study the behaviors of mean end-to-end distance and specific heat of a two-dimensional intrinsically curved semiflexible biopolymer with a hard-core excluded volume interaction. We find the mean square end-to-end distance R_N²∝N^β at large N, with N being the number of monomers. Both β and proportional constant are dependent on the reduced bending rigidity κ and intrinsic curvature c. The larger the c, the smaller the proportional constant, and 1.5≥β≥1. Up to a moderate κ=κ_c, or down to a moderate temperature T=T_c, β=1.5, the same as that of a self-avoiding random walk, and the larger the intrinsic curvature, the smaller the κ_c. However, at a large κ or a low temperature, β is close to 1, and the conformation of the biopolymer can be more compact than that of a random walk. There is an intermediate regime with 1.5 > β > 1 and the transition from β=1.5 to β=1 is smooth. The specific heat of the system increases smoothly with increasing κ or there is no peak in the specific heat. Therefore, a nonvanishing intrinsic curvature seriously affects the thermal properties of a semiflexible biopolymer, but there is no phase transition in the system.

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Multiple-predators-based capture process on complex networks

濮存来, 李杰, 陈荣斌, 许忠奇

2017 (3): 38901-038901. doi: 10.1088/1674-1056/26/3/038901

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The predator/prey (capture) problem is a prototype of many network-related applications. We study the capture process on complex networks by considering multiple predators from multiple sources. In our model, some lions start from multiple sources simultaneously to capture the lamb by biased random walks, which are controlled with a free parameter α. We derive the distribution of the lamb's lifetime and the expected lifetime <T>. Through simulation, we find that the expected lifetime drops substantially with the increasing number of lions. Moreover, we study how the underlying topological structure affects the capture process, and obtain that locating on small-degree nodes is better than on large-degree nodes to prolong the lifetime of the lamb. The dense or homogeneous network structures are against the survival of the lamb. We also discuss how to improve the capture efficiency in our model.

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Link prediction in complex networks via modularity-based belief propagation

赖大荣, 舒欣

2017 (3): 38902-038902. doi: 10.1088/1674-1056/26/3/038902

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Link prediction aims at detecting missing, spurious or evolving links in a network, based on the topological information and/or nodes' attributes of the network. Under the assumption that the likelihood of the existence of a link between two nodes can be captured by nodes' similarity, several methods have been proposed to compute similarity directly or indirectly, with information on node degree. However, correctly predicting links is also crucial in revealing the link formation mechanisms and thus in providing more accurate modeling for networks. We here propose a novel method to predict links by incorporating stochastic-block-model link generating mechanisms with node degree. The proposed method first recovers the underlying block structure of a network by modularity-based belief propagation, and based on the recovered block structural information it models the link likelihood between two nodes to match the degree sequence of the network. Experiments on a set of real-world networks and synthetic networks generated by stochastic block model show that our proposed method is effective in detecting missing, spurious or evolving links of networks that can be well modeled by a stochastic block model. This approach efficiently complements the toolbox for complex network analysis, offering a novel tool to model links in stochastic block model networks that are fundamental in the modeling of real world complex networks.

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The interaction between stratospheric monthly mean regional winds and sporadic-E

Kenan &#;etin,Osman &#;zcan,Serhat Korlael&#;i

2017 (3): 39401-039401. doi: 10.1088/1674-1056/26/3/039401

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In the present study, a statistical investigation is carried out to explore whether there is a relationship between the critical frequency (foEs) of the sporadic-E layer that is occasionally seen on the E region of the ionosphere and the quasi-biennial oscillation (QBO) that flows in the east-west direction in the equatorial stratosphere. Multiple regression model as a statistical tool was used to determine the relationship between variables. In this model, the stationarity of the variables (foEs and QBO) was firstly analyzed for each station (Cocos Island, Gibilmanna, Niue Island, and Tahiti). Then, a co-integration test was made to determine the existence of a long-term relationship between QBO and foEs. After verifying the presence of a long-term relationship between the variables, the magnitude of the relationship between variables was further determined using the multiple regression model. As a result, it is concluded that the variations in foEs were explainable with QBO measured at 10 hPa altitude at the rate of 69%, 94%, 79%, and 58% for Cocos Island, Gibilmanna, Niue Island, and Tahiti stations, respectively. It is observed that the variations in foEs were explainable with QBO measured at 70 hPa altitude at the rate of 66%, 69%, 53%, and 47% for Cocos Island, Gibilmanna, Niue Island, and Tahiti stations, respectively.

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Error analysis of the piston estimation method in dispersed fringe sensor

李杨, 王胜千, 饶长辉

2017 (3): 39501-039501. doi: 10.1088/1674-1056/26/3/039501

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Dispersed fringe sensor (DFS) is an important phasing sensor of next-generation optical astronomical telescopes. The measurement errors induced by the measurement noise of three piston estimation methods for the DFS including least-squared fitting (LSF) method, frequency peak location (FPL) method and main peak position (MPP) method, are analyzed theoretically and validated experimentally in this paper. The experimental results coincide well with the theoretical analyses. The MPP, FPL, LSF are used respectively when the DFS operates with broadband light (central wavelength: 706 nm, bandwidth: 23 nm). The corresponding root mean square (RMS) value of estimated piston error can be achieved to be 1 nm, 3 nm, 26 nm, respectively. Additionally, the range of DFS with the FPL can be more than 100 μm at the same time. The FPL method can work well both in coarse and fine phasing stages with acceptable accuracy, compared with LSF method and MPP method.

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