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HighLights More»   
  • Spatially resolved gap closing in single Josephson junctions constructed on Bi2Te3 surface

    Yuan Pang(庞远), Junhua Wang(王骏华), Zhaozheng Lyu(吕昭征), Guang Yang(杨光), Jie Fan(樊洁), Guangtong Liu(刘广同), Zhongqing Ji(姬忠庆), Xiunian Jing(景秀年), Changli Yang(杨昌黎), Li Lu(吕力)
    Chin. Phys. B 2016, 25 (11): 117402
    Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators. Previously, we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi2Te3 surface. In this paper we report further investiga...

     
  • Large scale fabrication of nitrogen vacancy-embedded diamond nanostructures for single-photon source applications

    Qianqing Jiang(姜倩晴), Wuxia Li(李无瑕), Chengchun Tang(唐成春), Yanchun Chang(常彦春), Tingting Hao(郝婷婷), Xinyu Pan(潘新宇), Haitao Ye(叶海涛), Junjie Li(李俊杰), Changzhi Gu(顾长志)
    Chin. Phys. B 2016, 25 (11): 118105
    Color centers in diamond are prominent candidates for generating and manipulating quantum states of light, even at room temperature. However, the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, we fabricated arrays of...

     
  • High performance photodetectors based on high quality InP nanowires

    Yan-Kun Yang(杨燕琨), Tie-Feng Yang(杨铁锋), Hong-Lai Li(李洪来), Zhao-Yang Qi(祁朝阳), Xin-Liang Chen(陈新亮), Wen-Qiang Wu(吴文强), Xue-Lu Hu(胡学鹿), Peng-Bin He(贺鹏斌), Ying Jiang(蒋英), Wei Hu(胡伟), Qing-Lin Zhang(张清林), Xiu-Juan Zhuang(庄秀娟), Xiao-Li Zhu(朱小莉), An-Lian Pan(潘安练)
    Chin. Phys. B 2016, 25 (11): 118106
    In this paper, small diameter InP nanowires with high crystal quality were synthesized through a chemical vapor deposition method. Benefitting from the high crystallinity and large specific surface area of InP nanowires, the simply constructed photodetector demonstrates a high responsivity of up to ...

     
Chin. Phys. B  
  Chin. Phys. B--2016, Vol.25, No.11
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TOPICAL REVIEW—Topological electronic states

Quantum transport properties of the three-dimensional Dirac semimetal Cd3As2 single crystals

Lan-Po He(何兰坡), Shi-Yan Li(李世燕)
Chin. Phys. B, 2016, 25 (11): 117105 doi: 10.1088/1674-1056/25/11/117105
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The discovery of the three-dimensional Dirac semimetals have expanded the family of topological materials, and attracted massive attentions in recent few years. In this short review, we briefly overview the quantum transport properties of a well-studied three-dimensional Dirac semimetal, Cd3As2. These unusual transport phenomena include the unexpected ultra-high charge mobility, large linear magnetoresistivity, remarkable Shubnikov-de Hass oscillations, and the evolution of the nontrivial Berry's phase. These quantum transport properties not only reflect the novel electronic structure of Dirac semimetals, but also give the possibilities for their future device applications.

Topological nodal line semimetals

Chen Fang(方辰), Hongming Weng(翁红明), Xi Dai(戴希), Zhong Fang(方忠)
Chin. Phys. B, 2016, 25 (11): 117106 doi: 10.1088/1674-1056/25/11/117106
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We review the recent, mainly theoretical, progress in the study of topological nodal line semimetals in three dimensions. In these semimetals, the conduction and the valence bands cross each other along a one-dimensional curve in the three-dimensional Brillouin zone, and any perturbation that preserves a certain symmetry group (generated by either spatial symmetries or time-reversal symmetry) cannot remove this crossing line and open a full direct gap between the two bands. The nodal line(s) is hence topologically protected by the symmetry group, and can be associated with a topological invariant. In this review, (i) we enumerate the symmetry groups that may protect a topological nodal line; (ii) we write down the explicit form of the topological invariant for each of these symmetry groups in terms of the wave functions on the Fermi surface, establishing a topological classification; (iii) for certain classes, we review the proposals for the realization of these semimetals in real materials; (iv) we discuss different scenarios that when the protecting symmetry is broken, how a topological nodal line semimetal becomes Weyl semimetals, Dirac semimetals, and other topological phases; and (v) we discuss the possible physical effects accessible to experimental probes in these materials.

Electron localization in ultrathin films of three-dimensional topological insulators

Jian Liao(廖剑), Gang Shi(史刚), Nan Liu(刘楠), Yongqing Li(李永庆)
Chin. Phys. B, 2016, 25 (11): 117201 doi: 10.1088/1674-1056/25/11/117201
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The recent discovery of three-dimensional (3D) topological insulators (TIs) has provided a fertile ground for obtaining further insights into electron localization in condensed matter systems. In the past few years, a tremendous amount of research effort has been devoted to investigate electron transport properties of 3D TIs and their low dimensional structures in a wide range of disorder strength, covering transport regimes from weak antilocalization to strong localization. The knowledge gained from these studies not only offers sensitive means to probe the surface states of 3D TIs but also forms a basis for exploring novel topological phases. In this article, we briefly review the main experimental progress in the study of the localization in 3D TIs, with a focus on the latest results on ultrathin TI films. Some new transport data will also be presented in order to complement those reported previously in the literature.

Weak antilocalization and interaction-induced localization of Dirac and Weyl Fermions in topological insulators and semimetals

Hai-Zhou Lu(卢海舟), Shun-Qing Shen(沈顺清)
Chin. Phys. B, 2016, 25 (11): 117202 doi: 10.1088/1674-1056/25/11/117202
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Weak localization and antilocalization are quantum transport phenomena that arise from the quantum interference in disordered metals. At low temperatures, they can give distinct temperature and magnetic field dependences in conductivity, allowing the symmetry of the system to be explored. In the past few years, they have also been observed in newly emergent topological materials, including topological insulators and topological semimetals. In contrast from the conventional electrons, in these new materials the quasiparticles are described as Dirac or Weyl fermions. In this article, we review our recent efforts on the theories of weak antilocalization and interaction-induced localization for Dirac and Weyl fermions in topological insulators and topological semimetals.

Recent observations of negative longitudinal magnetoresistance in semimetal

Xi-Tong Xu(许锡童), Shuang Jia(贾爽)
Chin. Phys. B, 2016, 25 (11): 117204 doi: 10.1088/1674-1056/25/11/117204
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The discovery of Dirac semimetal and Weyl semimetal has motivated a growing passion for investigating the unique magneto-transport properties in the topological materials. A Weyl semimetal can host Weyl fermions as its low-energy quasi-particle excitations, and therefore perform exotic features analogous to those in high-energy physics, such as the violation of the chiral charge conservation known as the chiral anomaly. One of the electrical transport signatures of the chiral anomaly is the Adler-Bell-Jackiw (ABJ) anomaly which presents as a negative magnetoresistance when the magnetic field and the current are parallel. Very recently, numerous experiments reported negative longitudinal magnetoresistance (NLMR) in topological materials, but the details of the measurement results are various. Here the materials and the corresponding experiment results are briefly reviewed. Besides the plausible explanation of the ABJ anomaly, some other origins of the NLMR are also discussed.

Quantum anomalous Hall effect in real materials

Jiayong Zhang(张加永), Bao Zhao(赵宝), Tong Zhou(周通), Zhongqin Yang(杨中芹)
Chin. Phys. B, 2016, 25 (11): 117308 doi: 10.1088/1674-1056/25/11/117308
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Under a strong magnetic field, the quantum Hall (QH) effect can be observed in two-dimensional electronic gas systems. If the quantized Hall conductivity is acquired in a system without the need of an external magnetic field, then it will give rise to a new quantum state, the quantum anomalous Hall (QAH) state. The QAH state is a novel quantum state that is insulating in the bulk but exhibits unique conducting edge states topologically protected from backscattering and holds great potential for applications in low-power-consumption electronics. The realization of the QAH effect in real materials is of great significance. In this paper, we systematically review the theoretical proposals that have been brought forward to realize the QAH effect in various real material systems or structures, including magnetically doped topological insulators, graphene-based systems, silicene-based systems, two-dimensional organometallic frameworks, quantum wells, and functionalized Sb(111) monolayers, etc. Our paper can help our readers to quickly grasp the recent developments in this field.

Thermoelectric effects and topological insulators

Yong Xu(徐勇)
Chin. Phys. B, 2016, 25 (11): 117309 doi: 10.1088/1674-1056/25/11/117309
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The recent discovery of topological insulators (TIs) offers new opportunities for the development of thermoelectrics, because many TIs (like Bi2Te3) are excellent thermoelectric (TE) materials. In this review, we will first describe the general TE properties of TIs and show that the coexistence of the bulk and boundary states in TIs introduces unusual TE properties, including strong size effects and an anomalous Seebeck effect. Importantly, the TE figure of merit zT of TIs is no longer an intrinsic property, but depends strongly on the geometric size. The geometric parameters of two-dimensional TIs can be tuned to enhance zT to be significantly greater than 1. Then a few proof-of-principle experiments on three-dimensional TIs will be discussed, which observed unconventional TE phenomena that are closely related to the topological nature of the materials. However, current experiments indicate that the metallic surface states, if their advantage of high mobility is not fully utilized, would be detrimental to TE performance. Finally, we provide an outlook for future work on topological materials, which offers great possibilities to discover exotic TE effects and may lead to significant breakthroughs in improving zT.

Topological hierarchy matters–topological matters with superlattices of defects

Jing He(何敬), Su-Peng Kou(寇谡鹏)
Chin. Phys. B, 2016, 25 (11): 117310 doi: 10.1088/1674-1056/25/11/117310
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Topological insulators/superconductors are new states of quantum matter with metallic edge/surface states. In this paper, we review the defects effect in these topological states and study new types of topological matters–topological hierarchy matters. We find that both topological defects (quantized vortices) and non topological defects (vacancies) can induce topological mid-gap states in the topological hierarchy matters after considering the superlattice of defects. These topological mid-gap states have nontrivial topological properties, including the nonzero Chern number and the gapless edge states. Effective tight-binding models are obtained to describe the topological mid-gap states in the topological hierarchy matters.

Disorder effects in topological states: Brief review of the recent developments

Binglan Wu(吴冰兰), Juntao Song(宋俊涛), Jiaojiao Zhou(周娇娇), Hua Jiang(江华)
Chin. Phys. B, 2016, 25 (11): 117311 doi: 10.1088/1674-1056/25/11/117311
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Disorder inevitably exists in realistic samples, manifesting itself in various exotic properties for the topological states. In this paper, we summarize and briefly review the work completed over the last few years, including our own, regarding recent developments in several topics about disorder effects in topological states. For weak disorder, the robustness of topological states is demonstrated, especially for both quantum spin Hall states with Z2=1 and size induced nontrivial topological insulators with Z2=0. For moderate disorder, by increasing the randomness of both the impurity distribution and the impurity induced potential, the topological insulator states can be created from normal metallic or insulating states. These phenomena and their mechanisms are summarized. For strong disorder, the disorder causes a metal-insulator transition. Due to their topological nature, the phase diagrams are much richer in topological state systems. Finally, the trends in these areas of disorder research are discussed.

Two-dimensional topological insulators with large bulk energy gap

Z Q Yang(杨中强), Jin-Feng Jia(贾金锋), Dong Qian(钱冬)
Chin. Phys. B, 2016, 25 (11): 117312 doi: 10.1088/1674-1056/25/11/117312
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Two-dimensional (2D) topological insulators (TIs, or quantum spin Hall insulators) are special insulators that possess bulk 2D electronic energy gap and time-reversal symmetry protected one-dimensional (1D) edge state. Carriers in the edge state have the property of spin-momentum locking, enabling dissipation-free conduction along the 1D edge. The existence of 2D TIs was confirmed by experiments in semiconductor quantum wells. However, the 2D bulk gaps in those quantum wells are extremely small, greatly limiting potential application in future electronics and spintronics. Despite this limitation, 2D TIs with a large bulk gap attracted plenty of interest. In this paper, recent progress in searching for TIs with a large bulk gap is reviewed briefly. We start by introducing some theoretical predictions of these new materials and then discuss some recent important achievements in crystal growth and characterization.

Electronic properties of SnTe-class topological crystalline insulator materials

Jianfeng Wang(王建峰), Na Wang(王娜), Huaqing Huang(黄华卿), Wenhui Duan(段文晖)
Chin. Phys. B, 2016, 25 (11): 117313 doi: 10.1088/1674-1056/25/11/117313
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The rise of topological insulators in recent years has broken new ground both in the conceptual cognition of condensed matter physics and the promising revolution of the electronic devices. It also stimulates the explorations of more topological states of matter. Topological crystalline insulator is a new topological phase, which combines the electronic topology and crystal symmetry together. In this article, we review the recent progress in the studies of SnTe-class topological crystalline insulator materials. Starting from the topological identifications in the aspects of the bulk topology, surface states calculations, and experimental observations, we present the electronic properties of topological crystalline insulators under various perturbations, including native defect, chemical doping, strain, and thickness-dependent confinement effects, and then discuss their unique quantum transport properties, such as valley-selective filtering and helicity-resolved functionalities for Dirac fermions. The rich properties and high tunability make SnTe-class materials promising candidates for novel quantum devices.

GENERAL

Conformal structure-preserving method for damped nonlinear Schrödinger equation

Hao Fu(傅浩), Wei-En Zhou(周炜恩), Xu Qian(钱旭), Song-He Song(宋松和), Li-Ying Zhang(张利英)
Chin. Phys. B, 2016, 25 (11): 110201 doi: 10.1088/1674-1056/25/11/110201
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In this paper, we propose a conformal momentum-preserving method to solve a damped nonlinear Schrödinger (DNLS) equation. Based on its damped multi-symplectic formulation, the DNLS system can be split into a Hamiltonian part and a dissipative part. For the Hamiltonian part, the average vector field (AVF) method and implicit midpoint method are employed in spatial and temporal discretizations, respectively. For the dissipative part, we can solve it exactly. The proposed method conserves the conformal momentum conservation law in any local time-space region. With periodic boundary conditions, this method also preserves the total conformal momentum and the dissipation rate of momentum exactly. Numerical experiments are presented to demonstrate the conservative properties of the proposed method.

Fractal dynamics in the ionization of helium Rydberg atoms

Xiulan Xu(徐秀兰), Yanhui Zhang(张延惠), Xiangji Cai(蔡祥吉), Guopeng Zhao(赵国鹏), Lisha Kang(康丽莎)
Chin. Phys. B, 2016, 25 (11): 110301 doi: 10.1088/1674-1056/25/11/110301
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We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory. By introducing a fractal approach to describe the chaotic dynamical behavior of the ionization, we identify the fractal self-similarity structure of the escape time versus the distribution of the initial launch angles of electrons, and find that the self-similarity region shifts toward larger initial launch angles with a decrease in the scaled energy. We connect the fractal structure of the escape time plot to the escape dynamics of ionized electrons. Of particular note is that the fractal dimensions are sensitively controlled by the scaled energy and magnetic field, and exhibit excellent agreement with the chaotic extent of the ionization systems for both helium and hydrogen Rydberg atoms. It is shown that, besides the electric and magnetic fields, core scattering is a primary factor in the fractal dynamics.

General coarsened measurement references for revelation of a classical world

Dong Xie(谢东), Chunling Xu(徐春玲), Anmin Wang(王安民)
Chin. Phys. B, 2016, 25 (11): 110302 doi: 10.1088/1674-1056/25/11/110302
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It has been found that for a fixed degree of fuzziness in the coarsened references of measurements, the quantum-to-classical transition can be observed independent of the macroscopicity of the quantum state. We explore a general situation that the degree of fuzziness can change with the rotation angle between two states (different rotation angles represent different references). The fuzziness of reference comes from two kinds of fuzziness:the Hamiltonian (rotation frequency) and the timing (rotation time). For the fuzziness of the Hamiltonian alone, the degree of fuzziness for the reference will change with the rotation angle between two states, and the quantum effects can still be observed with any degree of fuzziness of Hamiltonian. For the fuzziness of timing, the degree of the coarsening reference is unchanged with the rotation angle. During the rotation of the measurement axis, the decoherence environment can also help the classical-to-quantum transition due to changing the direction of the measurement axis.

Amplifying and freezing of quantum coherence using weak measurement and quantum measurement reversal

Lian-Wu Yang(杨连武), Yun-Jie Xia(夏云杰)
Chin. Phys. B, 2016, 25 (11): 110303 doi: 10.1088/1674-1056/25/11/110303
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We analyze universal conditions where the l1 norm and relative entropy of coherence are amplified and frozen under identical bit-flip channels; that is, using pre-measurements (quantum weak measurements or quantum measurement reversals) on the systems before undergoing local bit-flip channels. With the option of quantum weak measurements or quantum measurement reversals, the measurement strength and the success probability are all determined by the initial state of the quantum system.

Stopping time of a one-dimensional bounded quantum walk

Hao Luo(骆浩), Xiang Zhan(詹翔), Peng Zhang(张芃), Peng Xue(薛鹏)
Chin. Phys. B, 2016, 25 (11): 110304 doi: 10.1088/1674-1056/25/11/110304
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The stopping time of a one-dimensional bounded classical random walk (RW) is defined as the number of steps taken by a random walker to arrive at a fixed boundary for the first time. A quantum walk (QW) is a non-trivial generalization of RW, and has attracted a great deal of interest from researchers working in quantum physics and quantum information. In this paper, we develop a method to calculate the stopping time for a one-dimensional QW. Using our method, we further compare the properties of stopping time for QW and RW. We find that the mean value of the stopping time is the same for both of these problems. However, for short times, the probability for a walker performing a QW to arrive at the boundary is larger than that for a RW. This means that, although the mean stopping time of a quantum and classical walker are the same, the quantum walker has a greater probability of arriving at the boundary earlier than the classical walker.

Cryptanalysis of quantum broadcast communication and authentication protocol with a one-time pad

Ya Cao(曹雅), Fei Gao(高飞)
Chin. Phys. B, 2016, 25 (11): 110305 doi: 10.1088/1674-1056/25/11/110305
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Chang et al. [Chin. Phys. B 23 010305 (2014)] have proposed a quantum broadcast communication and authentication protocol. However, we find that an intercept-resend attack can be preformed successfully by a potential eavesdropper, who will be able to destroy the authentication function. Afterwards, he or she can acquire the secret transmitted message or even modify it while escaping detection, by implementing an efficient man-in-the-middle attack. Furthermore, we show a simple scheme to defend this attack, that is, applying non-reusable identity strings.

Evolution of the vortex state in the BCS-BEC crossover of a quasi two-dimensional superfluid Fermi gas

Xuebing Luo(罗学兵), Kezhao Zhou(周可召), Zhidong Zhang(张志东)
Chin. Phys. B, 2016, 25 (11): 110306 doi: 10.1088/1674-1056/25/11/110306
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We use the path-integral formalism to investigate the vortex properties of a quasi-two dimensional (2D) Fermi superfluid system trapped in an optical lattice potential. Within the framework of mean-field theory, the cooper pair density, the atom number density, and the vortex core size are calculated from weakly interacting BCS regime to strongly coupled while weakly interacting BEC regime. Numerical results show that the atoms gradually penetrate into the vortex core as the system evolves from BEC to BCS regime. Meanwhile, the presence of the optical lattice allows us to analyze the vortex properties in the crossover from three-dimensional (3D) to 2D case. Furthermore, using a simple re-normalization procedure, we find that the two-body bound state exists only when the interaction is stronger than a critical one denoted by Gc which is obtained as a function of the lattice potential's parameter. Finally, we investigate the vortex core size and find that it grows with increasing interaction strength. In particular, by analyzing the behavior of the vortex core size in both BCS and BEC regimes, we find that the vortex core size behaves quite differently for positive and negative chemical potentials.

Cluster synchronization of community network with distributed time delays via impulsive control

Hui Leng(冷卉), Zhao-Yan Wu(吴召艳)
Chin. Phys. B, 2016, 25 (11): 110501 doi: 10.1088/1674-1056/25/11/110501
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Cluster synchronization is an important dynamical behavior in community networks and deserves further investigations. A community network with distributed time delays is investigated in this paper. For achieving cluster synchronization, an impulsive control scheme is introduced to design proper controllers and an adaptive strategy is adopted to make the impulsive controllers unified for different networks. Through taking advantage of the linear matrix inequality technique and constructing Lyapunov functions, some synchronization criteria with respect to the impulsive gains, instants, and system parameters without adaptive strategy are obtained and generalized to the adaptive case. Finally, numerical examples are presented to demonstrate the effectiveness of the theoretical results.

Application of the nonlinear time series prediction method of genetic algorithm for forecasting surface wind of point station in the South China Sea with scatterometer observations

Jian Zhong(钟剑), Gang Dong(董钢), Yimei Sun(孙一妹), Zhaoyang Zhang(张钊扬), Yuqin Wu(吴玉琴)
Chin. Phys. B, 2016, 25 (11): 110502 doi: 10.1088/1674-1056/25/11/110502
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The present work reports the development of nonlinear time series prediction method of genetic algorithm (GA) with singular spectrum analysis (SSA) for forecasting the surface wind of a point station in the South China Sea (SCS) with scatterometer observations. Before the nonlinear technique GA is used for forecasting the time series of surface wind, the SSA is applied to reduce the noise. The surface wind speed and surface wind components from scatterometer observations at three locations in the SCS have been used to develop and test the technique. The predictions have been compared with persistence forecasts in terms of root mean square error. The predicted surface wind with GA and SSA made up to four days (longer for some point station) in advance have been found to be significantly superior to those made by persistence model. This method can serve as a cost-effective alternate prediction technique for forecasting surface wind of a point station in the SCS basin.

Prompt efficiency of energy harvesting by magnetic coupling of an improved bi-stable system

Hai-Tao Li(李海涛), Wei-Yang Qin(秦卫阳)
Chin. Phys. B, 2016, 25 (11): 110503 doi: 10.1088/1674-1056/25/11/110503
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In order to improve the transform efficiency of bi-stable energy harvester (BEH), this paper proposes an advanced bi-stable energy harvester (ABEH), which is composed of two bi-stable beams coupling through their magnets. Theoretical analyzes and simulations for the ABEH are carried out. First, the mathematical model is established and its dynamical equations are derived. The formulas of magnetic force in two directions are given. The potential energy barrier of ABEH is reduced and the snap-through is liable to occur between potential wells. To demonstrate the ABEH's advantage in harvesting energy, comparisons between the ABEH and the BEH are carried out for both harmonic and stochastic excitations. Our results reveal that the ABEH's inter-well response can be elicited by a low-frequency excitation and the harvester can attain frequent jumping between potential wells at fairly weak random excitations. Thus, it can generate a higher output power. The present findings prove that the ABEH is preferable in harvesting energy and can be optimally designed such that it attains the best harvesting performance.

Anomalous transport in fluid field with random waiting time depending on the preceding jump length

Hong Zhang(张红), Guo-Hua Li(李国华)
Chin. Phys. B, 2016, 25 (11): 110504 doi: 10.1088/1674-1056/25/11/110504
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Anomalous (or non-Fickian) transport behaviors of particles have been widely observed in complex porous media. To capture the energy-dependent characteristics of non-Fickian transport of a particle in flow fields, in the present paper a generalized continuous time random walk model whose waiting time probability distribution depends on the preceding jump length is introduced, and the corresponding master equation in Fourier-Laplace space for the distribution of particles is derived. As examples, two generalized advection-dispersion equations for Gaussian distribution and lévy flight with the probability density function of waiting time being quadratic dependent on the preceding jump length are obtained by applying the derived master equation.
RAPID COMMUNICATION

Transport coefficients and mechanical response in hard-disk colloidal suspensions

Bo-Kai Zhang(张博凯), Jian Li(李健), Kang Chen(陈康), Wen-De Tian(田文得), Yu-Qiang Ma(马余强)
Chin. Phys. B, 2016, 25 (11): 116101 doi: 10.1088/1674-1056/25/11/116101
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We investigate the transport properties and mechanical response of glassy hard disks using nonlinear Langevin equation theory. We derive expressions for the elastic shear modulus and viscosity in two dimensions on the basis of thermal-activated barrier-hopping dynamics and mechanically accelerated motion. Dense hard disks exhibit phenomena such as softening elasticity, shear-thinning of viscosity, and yielding upon deformation, which are qualitatively similar to dense hard-sphere colloidal suspensions in three dimensions. These phenomena can be ascribed to stress-induced “landscape tilting”. Quantitative comparisons of these phenomena between hard disks and hard spheres are presented. Interestingly, we find that the density dependence of yield stress in hard disks is much more significant than in hard spheres. Our work provides a foundation for further generalizing the nonlinear Langevin equation theory to address slow dynamics and rheological behavior in binary or polydisperse mixtures of hard or soft disks.

Direct observation of the carrier transport process in InGaN quantum wells with a pn-junction

Haiyan Wu(吴海燕), Ziguang Ma(马紫光), Yang Jiang(江洋), Lu Wang(王禄), Haojun Yang(杨浩军), Yangfeng Li(李阳锋), Peng Zuo(左朋), Haiqiang Jia(贾海强), Wenxin Wang(王文新), Junming Zhou(周钧铭), Wuming Liu(刘伍明), Hong Chen(陈弘)
Chin. Phys. B, 2016, 25 (11): 117803 doi: 10.1088/1674-1056/25/11/117803
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A new mechanism of light-to-electricity conversion that uses InGaN/GaN QWs with a p-n junction is reported. According to the well established light-to-electricity conversion theory, quantum wells (QWs) cannot be used in solar cells and photodetectors because the photogenerated carriers in QWs usually relax to ground energy levels, owing to quantum confinement, and cannot form a photocurrent. We observe directly that more than 95% of the photoexcited carriers escape from InGaN/GaN QWs to generate a photocurrent, indicating that the thermionic emission and tunneling processes proposed previously cannot explain carriers escaping from QWs. We show that photoexcited carriers can escape directly from the QWs when the device is under working conditions. Our finding challenges the current theory and demonstrates a new prospect for developing highly efficient solar cells and photodetectors.

ATOMIC AND MOLECULAR PHYSICS

Theoretics-directed effect of copper or aluminum content on the ductility characteristics of Al-based (Al3Ti,AlTi,AlCu,AlTiCu2) intermetallic compounds

Yong Li(李勇), Xiao-Juan Ma(马小娟), Qi-Jun Liu(刘其军), Ge-Xing Kong(孔歌星), Hai-Xia Ma(马海霞), Wen-Peng Wang(王文鹏), Yi-Gao Wang(汪贻高), Zhen Jiao(焦振), Fu-Sheng Liu(刘福生), Zheng-Tang Liu(刘正堂)
Chin. Phys. B, 2016, 25 (11): 113101 doi: 10.1088/1674-1056/25/11/113101
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First-principle simulations have been applied to investigate the effect of copper (Cu) or aluminum (Al) content on the ductility of Al3Ti, AlTi, AlCu, and AlTiCu2 alloys. The mechanical stable and elastic properties of Al-based intermetallic compounds are researched by density functional theory with the generalized gradient approximation (DFT-GGA). The calculated lattice constants are in conformity with the previous experimental and theoretical data. The deduced elastic constants show that the investigated Al3Ti, AlTi, AlCu, and AlTiCu2 structures are mechanically stable. Shear modulus, Young's modulus, Poisson's ratio, and the ratio B/G have also been figured out by using reckoned elastic constants. A further analysis of Young's modulus and Poisson's ratio reveals that the third added element copper content has significant effects on the Al-Ti-based ICs ductile character.

Isotope shift calculations for D lines of stable and short-lived lithium nuclei

Geng-Hua Yu(余庚华), Peng-Yi Zhao(赵朋义), Bing-Ming Xu(徐炳明), Wei Yang(杨维), Xiao-Ling Zhu(朱晓玲)
Chin. Phys. B, 2016, 25 (11): 113102 doi: 10.1088/1674-1056/25/11/113102
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The isotope shifts (ISs) for the 2s2S1/2 to 2p2PJ (J=1/2, 3/2) transitions of the lithium nuclei including the stable and short-lived isotopes are calculated based on the multi-configuration Dirac-Hartree-Fock method and the relativistic configuration interaction approach. The results are in good agreement with the previous theoretical and experimental results within a deviation less than 0.05%. The methods used here could be applied to the IS calculations for other heavier Li-like ions and few-electron systems.

High-order harmonic generation of CO2 with different vibrational modes in an intense laser field

Hui Du(杜慧), Hong-Dan Zhang(张宏丹), Jun Zhang(张军), Hai-Feng Liu(刘海凤), Xue-Fei Pan(潘雪飞), Jing Guo(郭静), Xue-Shen Liu(刘学深)
Chin. Phys. B, 2016, 25 (11): 113201 doi: 10.1088/1674-1056/25/11/113201
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We apply the strong-field Lewenstein model to demonstrate the high-order harmonic generation of CO2 with three vibrational modes (balance vibration, bending vibration, and stretching vibration) driven by an intense laser field. The results show that the intensity of harmonic spectra is sensitive to molecular vibrational modes, and the high harmonic efficiency with stretching vibrational mode is the strongest. The underlying physical mechanism of the harmonic emission can be well explained by the corresponding ionization yield and the time-frequency analysis. Finally, we demonstrate the attosecond pulse generation with different vibrational modes and an isolated attosecond pulse with a duration of about 112 as is generated.

Fano resonance and magneto-optical Kerr rotaion in periodic Co/Ni complex plasmonic nanostructure

Le-Yi Chen(陈乐易), Zhi-Xiong Tang(唐志雄), Jin-Long Gao(高锦龙), Dao-Yong Li(李道勇), Cheng-Xin Lei(类成新), Zhen-Zhi Cheng(程振之), Shao-Long Tang(唐少龙), You-Wei Du(都有为)
Chin. Phys. B, 2016, 25 (11): 113301 doi: 10.1088/1674-1056/25/11/113301
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We report a pure ferromagnetic metallic magnetoplasmonic structure consisting of two-dimensional ordered Ni nanodisks array on Co film. With a sufficient height of the nanodisks, a steep and asymmetric Fano resonance can be excited in this structure. We attribute the fascinating spectral lineshape to the strong coupling between the excitation of surface plasmon polaritons at the interface and the localized surface plasmon resonance of nanodisks. The conclusion is fully confirmed by spectrum measurements in nanostructures with different heights. Furthermore, the enhancement and sign of the magneto-optical Kerr rotation in this structure are significantly modified by the Fano resonance.

Landau-Zener model for electron loss of low-energy negative fluorine ions to surface cations during grazing scattering on a LiF (001) surface

Wang Zhou(周旺), Meixiao Zhang(张鹛枭), Lihua Zhou(周利华), Hu Zhou(周虎), Yulong Ma(马玉龙), Yanling Guo(郭艳玲), Lin Chen(陈林), Ximeng Chen(陈熙萌)
Chin. Phys. B, 2016, 25 (11): 113401 doi: 10.1088/1674-1056/25/11/113401
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There is no available theoretical description of electron transfer from negative projectiles at a velocity below 0.1 a.u. during grazing scattering on insulating surfaces. In this low-velocity range, electron-capture and electron-loss processes coexist. For electron capture, the Demkov model has been successfully used to explain the velocity dependence of the negative-ion fraction formed from fast atoms during grazing scattering on insulating surfaces. For electron loss, we consider that an electron may be transferred from the formed ionic diabatic quasi-molecular state to the formed covalent diabatic quasi-molecular state by the crossing of the potential curves of negative projectiles approaching the surface cations, which can be described by the Landau-Zener two-energy-level crossing model. Combining these two models, we obtain good agreement between the experimental and calculated data for the F--LiF(001) collision system, which is briefly discussed.

Semi-analytical model for quasi-double-layer surface electrode ion traps

Jian Zhang(张见), Shuming Chen(陈书明), Yaohua Wang(王耀华)
Chin. Phys. B, 2016, 25 (11): 113701 doi: 10.1088/1674-1056/25/11/113701
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To realize scale quantum processors, the surface-electrode ion trap is an effective scaling approach, including single-layer, double-layer, and quasi-double-layer traps. To calculate critical trap parameters such as the trap center and trap depth, the finite element method (FEM) simulation was widely used, however, it is always time consuming. Moreover, the FEM simulation is also incapable of exhibiting the direct relationship between the geometry dimension and these parameters. To eliminate the problems above, House and Madsen et al. have respectively provided analytic models for single-layer traps and double-layer traps. In this paper, we propose a semi-analytical model for quasi-double-layer traps. This model can be applied to calculate the important parameters above of the ion trap in the trap design process. With this model, we can quickly and precisely find the optimum geometry design for trap electrodes in various cases.

Theoretical derivation and simulation of a versatileelectrostatic trap for cold polar molecules

Shengqiang Li(李胜强)
Chin. Phys. B, 2016, 25 (11): 113702 doi: 10.1088/1674-1056/25/11/113702
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We propose a versatile electrostatic trap scheme using several charged spherical electrodes and a bias electric field. We first give the two-ball scheme and derive the analytical solution of the electric field. In order to make a comparison, we also give the numerical solution calculated by the finite element software (Ansoft Maxwell). Considering the loading of cold polar molecules into the trap, we give the three-ball scheme. We first give the analytical and numerical solutions of the distribution of the electric field. Then we simulate the dynamic process of the loading and trapping cold molecules using the classical Monte Carlo method. We analyze the influence of the velocity of the incident molecular beam and the loading time on the loading efficiency. After that, we give the temperature of the trapped cold molecules. Our study shows that the loading efficiency can reach 82%, and the corresponding temperature of the trapped molecules is about 24.6 mK. At last, we show that the single well divides into two ones by increasing the bias electric field or decreasing the voltages applied to the spherical electrodes.

An optimized ion trap geometry to measure quadrupole shifts of 171Yb+ clocks

N Batra, B K Sahoo, S De
Chin. Phys. B, 2016, 25 (11): 113703 doi: 10.1088/1674-1056/25/11/113703
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We propose a new ion-trap geometry to carry out accurate measurements of the quadrupole shifts in the 171Yb ion. This trap will minimize the quadrupole shift due to the harmonic component of the confining potential by an order of magnitude. This will be useful to reduce the uncertainties in the clock frequency measurements of the 6s 2S1/2→4f136s2 2F7/2 and 6s 2S1/2→5d 2D3/2 transitions, from which we can deduce the precise values of the quadrupole moments (Θs) of the 4f136s2 2F7/2 and 5d 2D3/2 states. Moreover, it may be able to affirm the validity of the measured Θ value of the 4f136s2 2F7/2 state, for which three independent theoretical studies defer almost by one order of magnitude from the measurement. We also calculate Θs using the relativistic coupled-cluster (RCC) method. We use these Θ values to estimate the quadrupole shift that can be measured in our proposed ion trap experiment.

ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS

Application of optical diffraction method in designing phase plates

Ze-Min Lei(雷泽民), Xiao-Yan Sun(孙晓艳), Feng-Nian Lv(吕凤年), Zhen Zhang(张臻), Xing-Qiang Lu(卢兴强)
Chin. Phys. B, 2016, 25 (11): 114201 doi: 10.1088/1674-1056/25/11/114201
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Continuous phase plate (CPP), which has a function of beam shaping in laser systems, is one kind of important diffractive optics. Based on the Fourier transform of the Gerchberg-Saxton (G-S) algorithm for designing CPP, we proposed an optical diffraction method according to the real system conditions. A thin lens can complete the Fourier transform of the input signal and the inverse propagation of light can be implemented in a program. Using both of the two functions can realize the iteration process to calculate the near-field distribution of light and the far-field repeatedly, which is similar to the G-S algorithm. The results show that using the optical diffraction method can design a CPP for a complicated laser system, and make the CPP have abilities of beam shaping and phase compensation for the phase aberration of the system. The method can improve the adaptation of the phase plate in systems with phase aberrations.

Self-calibration wavelength modulation spectroscopy for acetylene detection based on tunable diode laser absorption spectroscopy

Qin-Bin Huang(黄秦斌), Xue-Mei Xu(许雪梅), Chen-Jing Li(李晨静), Yi-Peng Ding(丁一鹏), Can Cao(曹粲), Lin-Zi Yin(尹林子), Jia-Feng Ding(丁家峰)
Chin. Phys. B, 2016, 25 (11): 114202 doi: 10.1088/1674-1056/25/11/114202
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The expressions of the second harmonic (2f) signal are derived on the basis of absorption spectral and lock-in theories. A parametric study indicates that the phase shift between the intensity and wavelength modulation makes a great contribution to the 2f signal. A self-calibration wavelength modulation spectroscopy (WMS) method based on tunable diode laser absorption spectroscopy (TDLAS) is applied, combining the advantages of ambient pressure, temperature suppression, and phase-shift influences elimination. Species concentration is retrieved simultaneously from selected 2f signal pairs of measured and reference WMS-2f spectra. The absorption line of acetylene (C2H2) at 1530.36 nm near-infrared is selected to detect C2H2 concentrations in the range of 0-400 ppmv. System sensitivity, detection precision and limit are markedly improved, demonstrating that the self-calibration method has better detecting performance than the conventional WMS.

Theoretical simulation of 87Rb absorption spectrum in a thermal cell

Hong Cheng(成红), Shan-Shan Zhang(张珊珊), Pei-Pei Xin(辛培培), Yuan Cheng(程元), Hong-Ping Liu(刘红平)
Chin. Phys. B, 2016, 25 (11): 114203 doi: 10.1088/1674-1056/25/11/114203
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In this paper, we present a theoretical simulation of 87Rb absorption spectrum in a thermal cm-cell which is adaptive to the experimental observation. In experiment, the coupling and probe beams are configured to copropagate but perpendicular polarized, making up to five velocity selective optical pumping (VSOP) absorption dips able to be identified. A Λ-type electromagnetically induced transparency (EIT) is also observed for each group of velocity-selected atoms. The spectrum by only sweeping the probe beam can be decomposed into a combination of Doppler-broadened background and three VSOP dips for each group of velocity-selected atoms, accompanied by an EIT peak. This proposed theoretical model can be used to simulate the spectrum adaptive to the experimental observation by the non-linear least-square fit method. The fit for the high quality of experimental observation can determine valuable transition parameters such as decaying rates and coupling beam power accurately.

Observation of multi-Raman gain resonances in rubidium vapor

Jun Liu(刘俊), Dong Wei(卫栋), Jin-wen Wang(王金文), Ya Yu(余娅), Hua-jie Hu(胡华杰), Hong Gao(高宏), Fu-li Li(李福利)
Chin. Phys. B, 2016, 25 (11): 114204 doi: 10.1088/1674-1056/25/11/114204
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We present an experimental study of multi-Raman gain resonances in a hot rubidium vapor. The experiment is performed based on a high-efficiency four-wave mixing process due to the Raman-driven coherence in a double-Λ configuration. The Raman gain resonance for 85Rb atoms under a bias magnetic field is shown to be split into five or six peaks, depending on the orientation of the magnetic field. The formed multi-Raman gain resonances have potential applications in measurement of magnetic fields and generation of multi-frequency correlated twin beams.

Two-dimensional gain cross-grating based on spatial modulation of active Raman gain

Li Wang(王丽), Feng-Xue Zhou(周凤雪), Hong-Ju Guo(郭洪菊), Yue-Ping Niu(钮月萍), Shang-Qing Gong(龚尚庆)
Chin. Phys. B, 2016, 25 (11): 114205 doi: 10.1088/1674-1056/25/11/114205
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Based on the spatial modulation of active Raman gain, a two-dimensional gain cross-grating is theoretically proposed. As the probe field propagates along the z direction and passes through the intersectant region of the two orthogonal standing-wave fields in the x-y plane, it can be effectively diffracted into the high-order directions, and the zero-order diffraction intensity is amplified at the same time. In comparison with the two-dimensional electromagnetically induced cross-grating based on electromagnetically induced transparency, the two-dimensional gain cross-grating has much higher diffraction intensities in the first-order and the high-order directions. Hence, it is more suitable to be utilized as all-optical switching and routing in optical networking and communication.

Effects of magnetic field on photon-induced quantum transport in a single dot-cavity system

Nzar Rauf Abdullah, Aziz H Fatah, Jabar M A Fatah
Chin. Phys. B, 2016, 25 (11): 114206 doi: 10.1088/1674-1056/25/11/114206
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In this study, we show how a static magnetic field can control photon-induced electron transport through a quantum dot system coupled to a photon cavity. The quantum dot system is connected to two electron reservoirs and exposed to an external perpendicular static magnetic field. The propagation of electrons through the system is thus influenced by the static magnetic and the dynamic photon fields. It is observed that the photon cavity forms photon replica states controlling electron transport in the system. If the photon field has more energy than the cyclotron energy, then the photon field is dominant in the electron transport. Consequently, the electron transport is enhanced due to activation of photon replica states. By contrast, the electron transport is suppressed in the system when the photon energy is smaller than the cyclotron energy.

An efficient continuous-wave YVO4/Nd: YVO4/YVO4 self-Raman laser pumped by a wavelength-locked 878.9 nm laser diode

Li Fan(樊莉), Weiqian Zhao(赵伟倩), Xin Qiao(乔鑫), Changquan Xia(夏长权), Lichun Wang(汪丽春), Huibo Fan(范会博), Mingya Shen(沈明亚)
Chin. Phys. B, 2016, 25 (11): 114207 doi: 10.1088/1674-1056/25/11/114207
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We report an efficient continuous-wave self-Raman laser at 1176 nm based on a 20-mm-long composite YVO4/Nd:YVO4/YVO4 crystal and pumped by a wavelength-locked 878.9 nm diode laser. A maximum output power of 5.3 W is achieved at a pump power of 26 W, corresponding to an optical conversion efficiency of 20% and a slope efficiency of 21%. The Raman threshold for the diode pump power was only 0.92 W. The results reveal that in-band pumping by a wavelength-locked diode laser significantly enhances output power and efficiency of self-Raman lasers by virtue of improved pump absorption and relieved thermal loading.

Research of the use of silver nanowires as a current spreading layer on vertical-cavity surface-emitting lasers

Xia Guo(郭霞), Lei Shi(史磊), Chong Li(李冲), Jian Dong(董建), Bai Liu(刘白), Shuai Hu(胡帅), Yan He(何艳)
Chin. Phys. B, 2016, 25 (11): 114208 doi: 10.1088/1674-1056/25/11/114208
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Silver nanowire (AgNW) film was proposed to apply on the surface of the vertical-cavity surface-emitting lasers (VCSELs) with large aperture in order to obtain a uniform current distribution in the active region and a better optical beam quality. Optimization of the AgNW film was carried out with the sheet resistance of 28.4 Ω/sq and the optical transmission of 94.8% at 850 nm. The performance of VCSELs with and without AgNW film was studied. When the AgNW film was applied to the surface of VCSELs, due to its better current spreading effect, the maximum output optical power increased from 23.4 mW to 24.4 mW, the lasing wavelength redshift decreased from 0.085 nm/mA to 0.077 nm/mA, the differential resistance decreased from 23.95 Ω to 21.13 Ω, and the far field pattern at 50 mA decreased from 21.6° to 19.2°. At the same time, the near field test results showed that the light in the aperture was more uniform, and the far field exhibited a better single peak characteristic. Various results showed that VCSELs with AgNW on the surface showed better beam quality.

Coupled-resonator-induced transparency in two microspheres as the element of angular velocity sensing

Kun Qian(钱坤), Jun Tang(唐军), Hao Guo(郭浩), Wei Zhang(张伟), Jian-Hua Liu(刘建华), Jun Liu(刘俊), Chen-Yang Xue(薛晨阳), Wen-Dong Zhang(张文栋)
Chin. Phys. B, 2016, 25 (11): 114209 doi: 10.1088/1674-1056/25/11/114209
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We proposed a two-coupled microsphere resonator structure as the element of angular velocity sensing under the Sagnac effect. We analyzed the theoretical model of the two coupled microspheres, and derived the coupled-resonator-induced transparency (CRIT) transfer function, the effective phase shift, and the group delay. Experiments were also carried out to demonstrate the CRIT phenomenon in the two-coupled microsphere resonator structure. We calculated that the group index of the two-coupled sphere reaches ng=180.46, while the input light at a wavelength of 1550 nm.

Tracking molecular structure deformation of nitrobenzene and its torsion vibration coupling by intense pumping CARS

Chang Wang(王畅), Hong-Lin Wu(吴红琳), Yun-Fei Song(宋云飞), Xing He(何兴), Yan-Qiang Yang(杨延强), Duo-Wang Tan(谭多旺)
Chin. Phys. B, 2016, 25 (11): 114210 doi: 10.1088/1674-1056/25/11/114210
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The structural deformation induced by intense laser field of liquid nitrobenzene (NB) molecule, a typical molecule with restricting internal rotation, is tracked by time- and frequency-resolved coherent anti-Stokes. Raman spectroscopy (CARS) technique with an intense pump laser. The CARS spectra of liquid NB show that the NO2 torsional mode couples with the NO2 symmetric stretching mode, and the NB molecule undergoes ultrafast structural deformation with a relaxation time of 265 fs. The frequency of NO2 torsional mode in liquid NB (42 cm-1) at room temperature is found from the sum and difference combination bands involving the NO2 symmetric stretching mode and torsional mode in time- and frequency-resolved CARS spectra.

Ultra broadband flat dispersion tailoring on reversed-rib chalcogenide glass waveguide

Yanfen Zhai(翟彦芬), Renduo Qi(齐人铎), Chenzhi Yuan(袁晨智), Wei Zhang(张巍), Yidong Huang(黄翊东)
Chin. Phys. B, 2016, 25 (11): 114211 doi: 10.1088/1674-1056/25/11/114211
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In this paper, we introduce a horizontal slot in the reversed-rib chalcogenide glass waveguide to tailor its dispersion characteristics. The waveguide exhibits a flat and low dispersion over a wavelength range of 1080 nm, in which the dispersion fluctuates between -10.6 ps·nm-1·km-1 and+11.14 ps·nm-1·km-1. The dispersion tailoring effect is due to the mode field transfer from the reversed-rib waveguide to the slot with the increase of wavelength, which results in the extension of the low dispersion band. Moreover, the nonlinear coefficient and the phase-matching condition of the four-wave mixing process in this waveguide are studied, showing that the waveguide has great potential in nonlinear optical applications over a wide wavelength range.

Optimizing calculation of phase screen distribution with minimum condition along an inhomogeneous turbulent path

Wen-Yi Shao(邵文毅), Hao Xian(鲜浩)
Chin. Phys. B, 2016, 25 (11): 114212 doi: 10.1088/1674-1056/25/11/114212
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When building an experimental platform for light propagation along an inhomogeneous turbulent path, it is very essential to set up the reasonable distribution of phase screen. Based on multi-layered model of phase screen, an iterative optimization algorithm of phase screen position is given in this paper. Thereafter, the optimal position of phase screens is calculated under the Hufnagel-Valley5/7 and Hefei-day turbulence profile. The results show that the positions of phase screen calculated by the iterative algorithm can fit well with the turbulence profile rather than mechanically placed phase screens at equal distance. Compared with the uniform distribution of phase screens position, the residual phase error of the iterative algorithm decreases very significantly. The similarity degree between them is minimal when number of layers is equal to two.

High-reflectivity high-contrast grating focusing reflector on silicon-on-insulator wafer

Wenjing Fang(房文敬), Yongqing Huang(黄永清), Xiaofeng Duan(段晓峰), Kai Liu(刘凯), Jiarui Fei(费嘉瑞), Xiaomin Ren(任晓敏)
Chin. Phys. B, 2016, 25 (11): 114213 doi: 10.1088/1674-1056/25/11/114213
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A high-contrast grating (HCG) focusing reflector providing phase front control of reflected light and high reflectivity is proposed and fabricated. Basic design rules to engineer this category of structures are given in detail. A 1550 nm TM polarized incident light of 11.86 mm in focal length and 0.8320 in reflectivity is obtained in experiment. The wavelength dependence of the fabricated HCGs from 1530 nm to 1580 nm is also tested. The test results show that the focal length is in the range of 11.81-12 mm, which is close to the designed focal length of 15 mm. The reflectivity is almost above 0.56 within a bandwidth of 50 nm. At a distance of 11.86 mm, the light is focused to a round spot with the highest concentration, which is much smaller than the size of the incident beam. The FWHM of the reflected light beam decreases to 120 nm, and the intensity increases to 1.18.

A proposal for the generation of optical frequency comb in temperature insensitive microcavity

Xun Lei(雷勋), Dandan Bian(边丹丹), Shaowu Chen(陈少武)
Chin. Phys. B, 2016, 25 (11): 114214 doi: 10.1088/1674-1056/25/11/114214
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We numerically simulate the generation of an optical frequency comb (OFC) in a microring based on the traditional Si3N4 strip waveguide and a temperature compensated slot waveguide. The results show that OFCs are susceptible to temperature with strip waveguide while they can keep stable when temperature changes 10 K in either low-Q (105) or high Q (106) microcavity with the well-designed slot waveguide, which has great superiority in practical applications where the temperature drift of the cavity due to the intense pump or surrounding change is unavoidable.

Turbulence mitigation scheme based on multiple-user detection in an orbital-angular-momentum multiplexed system

Li Zou(邹丽), Le Wang(王乐), Sheng-Mei Zhao(赵生妹), Han-Wu Chen(陈汉武)
Chin. Phys. B, 2016, 25 (11): 114215 doi: 10.1088/1674-1056/25/11/114215
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Atmospheric turbulence (AT) induced crosstalk can significantly impair the performance of a free-space optical (FSO) communication link using orbital angular momentum (OAM) multiplexing. In this paper, we propose a multiple-user detection (MUD) turbulence mitigation scheme in an OAM-multiplexed FSO communication link. First, we present a MUD equivalent communication model for an OAM-multiplexed FSO communication link under AT. In the equivalent model, each input bit stream represents one user's information. The deformed OAM spatial modes caused by AT, instead of the pure OAM spatial modes, are used as information carriers, and the overlapping between the deformed OAM spatial modes are computed as the correlation coefficients between the users. Then, we present a turbulence mitigation scheme based on MUD idea to enhance AT tolerance of the OAM-multiplexed FSO communication link. In the proposed scheme, the crosstalk caused by AT is used as a useful component to deduce users' information. The numerical results show that the performance of the OAM-multiplexed communication link has greatly improved by the proposed scheme. When the turbulence strength C3in2 is 1×10-15 m-2/3, the transmission distance is 1000 m and the channel signal-to-noise ratio (SNR) is 26 dB, the bit-error-rate (BER) performance of four spatial multiplexed OAM modes lm=+1,+2,+3,+4 are all close to 10-5, and there is a 2-3 fold increase in the BER performance in comparison with those results without the proposed scheme. In addition, the proposed scheme is more effective for an OAM-multiplexed FSO communication link with a larger OAM mode topological charge interval. The proposed scheme is a promising direction for compensating the interference caused by AT in the OAM-multiplexed FSO communication link.

Plasmon-phonon coupling in graphene-hyperbolic bilayer heterostructures

Ge Yin(尹格), Jun Yuan(元军), Wei Jiang(姜玮), Jianfei Zhu(朱剑飞), Yungui Ma(马云贵)
Chin. Phys. B, 2016, 25 (11): 114216 doi: 10.1088/1674-1056/25/11/114216
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Polar dielectrics are important optical materials enabling the subwavelength manipulation of light in infrared due to their capability to excite phonon polaritons. In practice, it is highly desired to actively modify these hyperbolic phonon polaritons (HPPs) to optimize or tune the response of the device. In this work, we investigate the plasmonic material, a monolayer graphene, and study its hybrid structure with three kinds of hyperbolic thin films grown on SiO2 substrate. The inter-mode hybridization and their tunability have been thoroughly clarified from both the band dispersions and the mode patterns numerically calculated through a transfer matrix method. Our results show that these hybrid multilayer structures are of strong potentials for applications in plasmonic waveguides, modulators and detectors in infrared.

Low band gap frequencies and multiplexing properties in 1D and 2D mass spring structures

Arafa H Aly, Ahmed Mehaney
Chin. Phys. B, 2016, 25 (11): 114301 doi: 10.1088/1674-1056/25/11/114301
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This study reports on the propagation of elastic waves in 1D and 2D mass spring structures. An analytical and computation model is presented for the 1D and 2D mass spring systems with different examples. An enhancement in the band gap values was obtained by modeling the structures to obtain low frequency band gaps at small dimensions. Additionally, the evolution of the band gap as a function of mass value is discussed. Special attention is devoted to the local resonance property in frequency ranges within the gaps in the band structure for the corresponding infinite periodic lattice in the 1D and 2D mass spring system. A linear defect formed of a row of specific masses produces an elastic waveguide that transmits at the narrow pass band frequency. The frequency of the waveguides can be selected by adjusting the mass and stiffness coefficients of the materials constituting the waveguide. Moreover, we pay more attention to analyze the wave multiplexer and DE-multiplexer in the 2D mass spring system. We show that two of these tunable waveguides with alternating materials can be employed to filter and separate specific frequencies from a broad band input signal. The presented simulation data is validated through comparison with the published research, and can be extended in the development of resonators and MEMS verification.

Temperature-dependent specific heat of suspended platinum nanofilms at 80-380 K

Qin-Yi Li(李秦宜), Masahiro Narasaki(楢崎将弘), Koji Takahashi(高桥厚史), Tatsuya Ikuta(生田竜也), Takashi Nishiyama(西山贵史), Xing Zhang(张兴)
Chin. Phys. B, 2016, 25 (11): 114401 doi: 10.1088/1674-1056/25/11/114401
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Metallic nanofilms are important components of nanoscale electronic circuits and nanoscale sensors. The accurate characterization of the thermophysical properties of nanofilms is very important for nanoscience and nanotechnology. Currently, there is very little specific heat data for metallic nanofilms, and the existing measurements indicate distinct differences according to the nanofilm size. The present work reports the specific heats of 40-nm-thick suspended platinum nanofilms at 80-380 K and ~5×10-4 Pa using the 3ω method. Over 80-380 K, the specific heats of the Pt nanofilms range from 166-304 J/(kg·K), which are 1.65-2.60 times the bulk values, indicating significant size effects. These results are useful for both scientific research in nanoscale thermophysics and evaluating the transient thermal response of nanoscale devices.

Generalized Birkhoffian representation of nonholonomic systems and its discrete variational algorithm

Shixing Liu(刘世兴), Chang Liu(刘畅), Wei Hua(花巍), Yongxin Guo(郭永新)
Chin. Phys. B, 2016, 25 (11): 114501 doi: 10.1088/1674-1056/25/11/114501
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By using the discrete variational method, we study the numerical method of the general nonholonomic system in the generalized Birkhoffian framework, and construct a numerical method of generalized Birkhoffian equations called a self-adjoint-preserving algorithm. Numerical results show that it is reasonable to study the nonholonomic system by the structure-preserving algorithm in the generalized Birkhoffian framework.

Molecular dynamics simulation of structural change at metal/semiconductor interface induced by nanoindenter

Bing-Bing Zhao(赵兵兵), Ying Wang(王影), Chang Liu(刘畅), Xiao-Chun Wang(王晓春)
Chin. Phys. B, 2016, 25 (11): 114601 doi: 10.1088/1674-1056/25/11/114601
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The structures of the Si/Cu heterogenous interface impacted by a nanoindenter with different incident angles and depths are investigated in detail using molecular dynamics simulation. The simulation results suggest that for certain incident angles, the nanoindenter with increasing depth can firstly increase the stress of each atom at the interface and it then introduces more serious structural deformation of the Si/Cu heterogenous interface. A nanoindenter with increasing incident angle (absolute value) can increase the length of the Si or Cu extended atom layer. It is worth mentioning that when the incident angle of the nanoindenter is between -45° and 45°, these Si or Cu atoms near the nanoindenter reach a stable state, which has a lower stress and a shorter length of the Si or Cu extended atom layer than those of the other incident angles. This may give a direction to the planarizing process of very large scale integration circuits manufacture.

Induced magnetic field stagnation point flow of nanofluid past convectively heated stretching sheet with Buoyancy effects

Tanzila Hayat, S Nadeem
Chin. Phys. B, 2016, 25 (11): 114701 doi: 10.1088/1674-1056/25/11/114701
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This paper presents the buoyancy effects on the magneto-hydrodynamics stagnation point flow of an incompressible, viscous, and electrically conducting nanofluid over a vertically stretching sheet. The impacts of an induced magnetic field and viscous dissipation are taken into account. Both assisting and opposing flows are considered. The overseeing nonlinear partial differential equations with the associated boundary conditions are reduced to an arrangement of coupled nonlinear ordinary differential equations utilizing similarity transformations and are then illuminated analytically by using the optimal homotopy investigation strategy (OHAM). Graphs are introduced and examined for different parameters of the velocity, temperature, and concentration profile. Additionally, numerical estimations of the skin friction, local Nusselt number, and local Sherwood number are explored using numerical values.

Three-dimensional detonation cellular structures in rectangular ducts using an improved CESE scheme

Yang Shen(沈洋), Hua Shen(申华), Kai-Xin Liu(刘凯欣), Pu Chen(陈璞), De-Liang Zhang(张德良)
Chin. Phys. B, 2016, 25 (11): 114702 doi: 10.1088/1674-1056/25/11/114702
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The three-dimensional premixed H2-O2 detonation propagation in rectangular ducts is simulated using an in-house parallel detonation code based on the second-order space-time conservation element and solution element (CE/SE) scheme. The simulation reproduces three typical cellular structures by setting appropriate cross-sectional size and initial perturbation in square tubes. As the cross-sectional size decreases, critical cellular structures transforming the rectangular or diagonal mode into the spinning mode are obtained and discussed in the perspective of phase variation as well as decreasing of triple point lines. Furthermore, multiple cellular structures are observed through examples with typical aspect ratios. Utilizing the visualization of detailed three-dimensional structures, their formation mechanism is further analyzed.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

A divertor plasma configuration design method for tokamaks

Yong Guo(郭勇), Bing-Jia Xiao(肖炳甲), Lei Liu(刘磊), Fei Yang(杨飞), Yuehang Wang(汪悦航), Qinglai Qiu(仇庆来)
Chin. Phys. B, 2016, 25 (11): 115201 doi: 10.1088/1674-1056/25/11/115201
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The efficient and safe operation of large fusion devices strongly relies on the plasma configuration inside the vacuum chamber. It is important to construct the proper plasma equilibrium with a desired plasma configuration. In order to construct the target configuration, a shape constraint module has been developed in the tokamak simulation code (TSC), which controls the poloidal flux and the magnetic field at several defined control points. It is used to construct the double null, lower single null, and quasi-snowflake configurations for the required target shape and calculate the required PF coils current. The flexibility and practicability of this method have been verified by the simulated results.

One-dimensional hybrid simulation of the electrical asymmetry effectcaused by the fourth-order harmonic in dual-frequencycapacitively coupled plasma

Shuai Wang(王帅), Hai-Feng Long(龙海凤), Zhen-Hua Bi(毕振华), Wei Jiang(姜巍), Xiang Xu(徐翔), You-Nian Wang(王友年)
Chin. Phys. B, 2016, 25 (11): 115202 doi: 10.1088/1674-1056/25/11/115202
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A one-dimensional hybrid model was developed to study the electrical asymmetry effect (EAE) caused by the fourth-order harmonic in a dual-frequency capacitively coupled Ar plasma. The self-bias voltage caused by the fourth-order frequency changes periodically with the phase angle, and the cycle of self-bias with the phase angle is π/2, which is half of that in the second-order case. The influence of the phase angle between the fundamental and its fourth-order frequency on the ion density profiles and the ion energy distributions (IEDs) were studied. Both the ion density profile and the IEDs can be controlled by the phase angle, which provides a convenient way to adjust the sheath characters without changing the main discharge parameters.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES

Quantitative determination of anti-structured defects applied to alloys of a wide chemical range

Jing Zhang(张静), Zheng Chen(陈铮), Yongxin Wang(王永欣), Yanli Lu(卢艳丽)
Chin. Phys. B, 2016, 25 (11): 116102 doi: 10.1088/1674-1056/25/11/116102
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Anti-structured defects bridge atom migration among heterogeneous sublattices facilitating diffusion but could also result in the collapse of ordered structure. Component distribution Ni75 AlxV25-x alloys are investigated using a microscopic phase field model to illuminate relations between anti-structured defects and composition, precipitate order, precipitate type, and phase stability. The Ni75 AlxV25-x alloys undergo single Ni3 V (stage I), dual Ni3 Al and Ni3 V (stage Ⅱ with Ni3 V prior; and stage Ⅲ with Ni3 Al prior), and single Ni3 Al (stage IV) with enhanced aluminum level. For Ni3 V phase, anti-structured defects (VNi1, NiV, except VNi2) and substitution defects (AlNi1, AlNi2, AlV) exhibit a positive correlation to aluminum in stage I, the positive trend becomes to negative correlation or smooth during stage Ⅱ. For Ni3 Al phase, anti-structured defects (AlNi, NiAl) and substitution defects (VNi, VAl) have a positive correlation to aluminum in stage Ⅱ, but NiAl goes down since stage Ⅲ and lasts to stage IV. VNi and VAl fluctuate when Ni3 Al precipitates prior, but go down drastically in stage IV. Precipitate type conversion of single Ni3 V/dual (Ni3 V+Ni3 Al) affects Ni3 V defects, while dual (Ni3 V+Ni3 Al)/single Ni3 Al has little effect on Ni3 Al defects. Precipitate order swap occurred in the dual phase region affects on Ni3 Al defects but not on Ni3 V.

Effect of Ar ion irradiation on the room temperature ferromagnetism of undoped and Cu-doped rutile TiO2 single crystals

Nan-Nan Xu(许楠楠), Gong-Ping Li(李公平), Qiao-Lu Lin(林俏露), Huan Liu(刘欢), Liang-Man Bao(包良满)
Chin. Phys. B, 2016, 25 (11): 116103 doi: 10.1088/1674-1056/25/11/116103
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Remarkable room-temperature ferromagnetism was observed both in undoped and Cu-doped rutile TiO2 single crystals (SCs). To tune their magnetism, Ar ion irradiation was quantitatively performed on the two crystals in which the saturation magnetizations for the samples were enhanced distinctively. The post-irradiation led to a spongelike layer in the near surface of the Cu-doped TiO2. Meanwhile, a new CuO-like species present in the sample was found to be dissolved after the post-irradiation. Analyzing the magnetization data unambiguously reveals that the experimentally observed ferromagnetism is related to the intrinsic defects rather than the exotic Cu ions, while these ions are directly involved in boosting the absorption in the visible region.

Thermophysical properties of iridium at finite temperature

Priyank Kumar, N K Bhatt, P R Vyas, V B Gohel
Chin. Phys. B, 2016, 25 (11): 116401 doi: 10.1088/1674-1056/25/11/116401
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The bulk properties of materials in an extreme environment such as high temperature and high pressure can be understood by studying anharmonic effects due to the vibration of lattice ions and thermally excited electrons. In this spirit, in the present paper, anharmonic effects are studied by using the recently proposed mean-field potential (MFP) approach and Mermin functional which arise due to the vibration of lattice ions and thermally excited electrons, respectively. The MFP experienced by a wanderer atom in the presence of surrounding atoms is constructed in terms of cold energy using the local form of the pseudopotential. We have calculated the temperature variation of several thermophysical properties in an extreme environment up to melting temperature. The results of our calculations are in excellent agreement with the experimental findings as well as the theoretical results obtained by using first principle methods. We conclude that presently used conjunction scheme (MFP+pseudopotential) is simple computationally, transparent physically, and accurate in the sense that the results generated are comparable and sometimes better than the results obtained by first principle methods. Local pseudopotential used is transferable to extreme environment without adjusting its parameters.

First-principles study of He trapping in η-Fe2C

Bing-Ling He(赫丙玲), Jin-Long Wang(王金龙), Zhi-Xue Tian(田之雪), Li-Juan Jiang(蒋利娟), Wei Song(宋薇), Bin Wang(王斌)
Chin. Phys. B, 2016, 25 (11): 116801 doi: 10.1088/1674-1056/25/11/116801
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The distribution of He in η-Fe2C has been studied by first-principles calculations. The formation energies of interstitial He and substitutional He (replacing Fe) are 3.76 eV and 3.49 eV, respectively, which are remarkably smaller than those in bcc Fe, indicating that He is more soluble in η-Fe2C than in bcc Fe. The binding potencies of both a substitutional-interstitial He pair (1.28 eV) and a substitutional-substitutional He pair (0.76 eV) are significantly weaker than those in bcc Fe. The binding energy between the two He atoms in an interstitial-interstitial He pair (0.31 eV) is the same as that in bcc Fe, but the diffusion barrier of interstitial He (0.35 eV) is much larger than that in bcc Fe, suggesting that it is more difficult for the interstitial He atom to agglomerate in η-Fe2C than in bcc Fe. Thus, self-trapping of He in η-Fe2C is less powerful than that in bcc Fe. As a consequence, small and dense η-Fe2C particles in ferritic steels might serve as scattered trapping centers for He, slow down He bubble growth at the initial stage, and make the steel more swelling resistant.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

Kernel polynomial representation for imaginary-time Green's functions in continuous-time quantum Monte Carlo impurity solver

Li Huang(黄理)
Chin. Phys. B, 2016, 25 (11): 117101 doi: 10.1088/1674-1056/25/11/117101
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Inspired by the recently proposed Legendre orthogonal polynomial representation for imaginary-time Green's functions G(τ), we develop an alternate and superior representation for G(τ) and implement it in the hybridization expansion continuous-time quantum Monte Carlo impurity solver. This representation is based on the kernel polynomial method, which introduces some integral kernel functions to filter the numerical fluctuations caused by the explicit truncations of polynomial expansion series and can improve the computational precision significantly. As an illustration of the new representation, we re-examine the imaginary-time Green's functions of the single-band Hubbard model in the framework of dynamical mean-field theory. The calculated results suggest that with carefully chosen integral kernel functions, whether the system is metallic or insulating, the Gibbs oscillations found in the previous Legendre orthogonal polynomial representation have been vastly suppressed and remarkable corrections to the measured Green's functions have been obtained.

Current spreading in GaN-based light-emitting diodes

Qiang Li(李强), Yufeng Li(李虞锋), Minyan Zhang(张敏妍), Wen Ding(丁文), Feng Yun(云峰)
Chin. Phys. B, 2016, 25 (11): 117102 doi: 10.1088/1674-1056/25/11/117102
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We have investigated the factors affecting the current spreading length (CSL) in GaN-based light-emitting diodes (LEDs) by deriving theoretical expressions and performing simulations with APSYS. For mesa-structure LEDs, the effects of both indium tin oxide (ITO) and n-GaN are taken into account for the first time, and a new Q factor is introduced to explain the effects of different current flow paths on the CSL. The calculations and simulations show that the CSL can be enhanced by increasing the thickness of the ITO layer and resistivity of the n-GaN layer, or by reducing the resistivity of the ITO layer and thickness of the n-GaN layer. The results provide theoretical support for calculating the CSL clearly and directly. For vertical-structure LEDs, the effects of resistivity and thickness of the CSL on the internal quantum efficiency (IQE) have been analyzed. The theoretical expression relating current density and the parameters (resistivity and thickness) of the CSL is obtained, and the results are then verified by simulation. The IQE under different current injection conditions is discussed. The effects of CSL resistivity play a key role at high current injection, and there is an optimal thickness for the largest IQE only at a low current injection.

Strain-induced magnetism in ReS2 monolayer with defects

Xiao-Ou Zhang(张小欧), Qing-Fang Li(李庆芳)
Chin. Phys. B, 2016, 25 (11): 117103 doi: 10.1088/1674-1056/25/11/117103
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We investigate the effects of strain on the electronic and magnetic properties of ReS2 monolayer with sulfur vacancies using density functional theory. Unstrained ReS2 monolayer with monosulfur vacancy (VS) and disulfur vacancy (V2S) both are nonmagnetic. However, as strain increases to 8%, VS-doped ReS2 monolayer appears a magnetic half-metal behavior with zero total magnetic moment. In particular, for V2S-doped ReS2 monolayer, the system becomes a magnetic semiconductor under 6% strain, in which Re atoms at vicinity of vacancy couple anti-ferromagnetically with each other, and continues to show a ferromagnetic metal characteristic with total magnetic moment of 1.60μ B under 7% strain. Our results imply that the strain-manipulated ReS2 monolayer with VS and V2S can be a possible candidate for new spintronic applications.

Crossover of large to small radius polaron in ionic crystals

M I Umo
Chin. Phys. B, 2016, 25 (11): 117104 doi: 10.1088/1674-1056/25/11/117104
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The crossover of large to small radius polaron is studied in terms of the inverse-relaxation time and temperature. It is found that the small radius polaron exists at higher temperature than the large radius polaron. A formula which relates the inverse-relaxation time to the ratio of arbitrary temperature and Debye temperature of the crystal is derived. The polaron crossover temperatures in NaCl and KBr are found from plotted graphs. The straight line emerging at the Debye temperature TD of a graph reflects the increase of the inverse relaxation time for increasing temperature up to the collapse of the small radius polaron. The relationship between the small and large radius polarons is found and known ratios of the effective and the bare masses of the electrons for the two substances are used to validate our results. The small radius polaron's mass is later compared with the mass obtained from the hopping formula and is found to be approximately equal. Finally, we point out that the crossover temperature is material-specific since it depends on the Debye and the effective dielectric function.

Spin noise spectroscopy of rubidium atomic gas under resonant and non-resonant conditions

Jian Ma(马健), Ping Shi(史平), Xuan Qian(钱轩), Wei Li(李伟), Yang Ji(姬扬)
Chin. Phys. B, 2016, 25 (11): 117203 doi: 10.1088/1674-1056/25/11/117203
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The spin fluctuation in rubidium atom gas is studied via all-optical spin noise spectroscopy (SNS). Experimental results show that the integrated SNS signal and its full width at half maximum (FWHM) strongly depend on the frequency detuning of the probe light under resonant and non-resonant conditions. The total integrated SNS signal can be well fitted with a single squared Faraday rotation spectrum and the FWHM dependence may be related to the absorption profile of the sample.

Small-signal modeling of GaN HEMT switch with a new intrinsic elements extraction method

Miao Geng(耿苗), Pei-Xian Li(李培咸), Wei-Jun Luo(罗卫军), Peng-Peng Sun(孙朋朋), Rong Zhang(张蓉), Xiao-Hua Ma(马晓华)
Chin. Phys. B, 2016, 25 (11): 117301 doi: 10.1088/1674-1056/25/11/117301
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A novel and accurate method is proposed to extract the intrinsic elements of the GaN high-electron-mobility transistor (HEMT) switch. The new extraction method is verified by comparing the simulated S-parameters with the measured data over the 5-40 GHz frequency range. The percentage errors Eij within 3.83% show the great agreement between the simulated S-parameters and the measured data.

Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire

M Munguía-Rodríguez, Ri Betancourt-Riera, Re Betancourt-Riera, R Riera, J M Nieto Jalil
Chin. Phys. B, 2016, 25 (11): 117302 doi: 10.1088/1674-1056/25/11/117302
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The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated, and expressions for the electronic states are presented. The system is modeled by considering T=0 K and also with a single parabolic conduction band, which is split into a subband system due to the confinement. The gain and differential cross-section for an electron Raman scattering process are obtained. In addition, the emission spectra for several scattering configurations are discussed, and interpretations of the singularities found in the spectra are given. The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.

Electronic transport of bilayer graphene with asymmetry line defects

Xiao-Ming Zhao(赵小明), Ya-Jie Wu(吴亚杰), Chan Chen(陈婵), Ying Liang(梁颖), Su-Peng Kou(寇谡鹏)
Chin. Phys. B, 2016, 25 (11): 117303 doi: 10.1088/1674-1056/25/11/117303
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In this paper, we study the quantum properties of a bilayer graphene with (asymmetry) line defects. The localized states are found around the line defects. Thus, the line defects on one certain layer of the bilayer graphene can lead to an electric transport channel. By adding a bias potential along the direction of the line defects, we calculate the electric conductivity of bilayer graphene with line defects using the Landauer-Büttiker theory, and show that the channel affects the electric conductivity remarkably by comparing the results with those in a perfect bilayer graphene. This one-dimensional line electric channel has the potential to be applied in nanotechnology engineering.

Effects of fluorine-based plasma treatment and thermal annealing on high-Al content AlGaN Schottky contact

Fang Liu(刘芳), Zhixin Qin(秦志新)
Chin. Phys. B, 2016, 25 (11): 117304 doi: 10.1088/1674-1056/25/11/117304
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Fluorine plasma treatment was used prior to the Schottky metal deposition on the undoped Al0.45Ga0.55N, which aimed at the solar-blind wavelength. After fluorine plasma treatment and before depositing the Ni/Au Schottky, the samples were thermal annealed in the N2 gas at 400℃. The reverse leakage current density of Al0.45Ga0.55N Schottky diode was reduced by 2 orders of magnitude at -10 V. The reverse leakage current density was reduced by 3 orders of magnitude after thermal annealing. Further capacitance-frequency analysis revealed that the fluorine-based plasma treatment reduces the surface states of AlGaN by one order of magnitude at different surface state energies. The capacitance-frequency analysis also proved that the concentration of carriers in AlGaN top is reduced through fluorine plasma treatment.

Recessed-gate quasi-enhancement-mode AlGaN/GaN high electron mobility transistors with oxygen plasma treatment

Yun-Long He(何云龙), Chong Wang(王冲), Min-Han Mi(宓珉瀚), Xue-Feng Zheng(郑雪峰), Meng Zhang(张濛), Meng-Di Zhao(赵梦荻), Heng-Shuang Zhang(张恒爽), Li-Xiang Chen(陈立香), Jin-Cheng Zhang(张进成), Xiao-Hua Ma(马晓华), Yue Hao(郝跃)
Chin. Phys. B, 2016, 25 (11): 117305 doi: 10.1088/1674-1056/25/11/117305
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In this paper, the enhancement-mode AlGaN/GaN HEMT combined with the low damage recessed-gate etching and the optimized oxygen plasma treatment was fabricated. Scanning electron microscope/energy dispersive spectrometer (SEM/EDS) method and x-ray photoelectron spectroscopy (XPS) method were used to confirm the formation of oxides. Based on the experimental results, the obtained enhancement-mode HEMT exhibited a threshold voltage of 0.5 V, a high peak transconductance of 210 mS/mm, and a maximum drain current of 610 mA/mm at the gate bias of 4 V. Meanwhile, the on/off current ratio of enhancement-mode HEMT was as high as 108, drain induced barrier lowering (DIBL) was as low as 5 mV/V, and subthreshold swing (SS) of 80 mV/decade was obtained. Compared with the conventional HEMT, the Schottky reverse current of enhancement-mode HEMT was three orders of magnitude lower, and the off-state breakdown voltage of which was higher. In addition, a power gain cutoff frequency (fmax) of the enhancement-mode HEMT was larger than that of the conventional one.

Charge transport and bipolar switching mechanismin a Cu/HfO2/Pt resistive switching cell

Tingting Tan(谭婷婷), Tingting Guo(郭婷婷), Zhihui Wu(吴志会), Zhengtang Liu(刘正堂)
Chin. Phys. B, 2016, 25 (11): 117306 doi: 10.1088/1674-1056/25/11/117306
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Bipolar resistance switching characteristics are investigated in Cu/sputtered-HfO2/Pt structure in the application of resistive random access memory (RRAM). The conduction mechanism of the structure is characterized to be SCLC conduction. The dependence of resistances in both high resistance state (HRS) and low resistance state (LRS) on the temperature and device area are studied. Then, the composition and chemical bonding state of Cu and Hf at Cu/HfO2 interface region are analyzed by x-ray photoelectron spectroscopy (XPS). Combining the electrical characteristics and the chemical structure at the interface, a model for the resistive switching effect in Cu/HfO2/Pt stack is proposed. According to this model, the generation and recovery of oxygen vacancies in the HfO2 film are responsible for the resistance change.

Spin-dependent thermoelectric effect and spin battery mechanism in triple quantum dots with Rashba spin-orbital interaction

Wei-Ping Xu(徐卫平), Yu-Ying Zhang(张玉颖), Qiang Wang(王强), Yi-Hang Nie(聂一行)
Chin. Phys. B, 2016, 25 (11): 117307 doi: 10.1088/1674-1056/25/11/117307
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We have studied spin-dependent thermoelectric transport through parallel triple quantum dots with Rashba spin-orbital interaction (RSOI) embedded in an Aharonov-Bohm interferometer connected symmetrically to leads using nonequilibrium Green's function method in the linear response regime. Under the appropriate configuration of magnetic flux phase and RSOI phase, the spin figure of merit can be enhanced and is even larger than the charge figure of merit. In particular, the charge and spin thermopowers as functions of both the magnetic flux phase and the RSOI phase present quadruple-peak structures in the contour graphs. For some specific configuration of the two phases, the device can provide a mechanism that converts heat into a spin voltage when the charge thermopower vanishes while the spin thermopower is not zero, which is useful in realizing the thermal spin battery and inducing a pure spin current in the device.

First-principles calculation of the structural,electronic,and magnetic properties of cubic perovskite RbXF3(X=Mn,V,Co,Fe)

Muhammad Raza ur rehman Hashmi, Muhammad Zafar, M Shakil, Atif Sattar, Shabbir Ahmed, S A Ahmad
Chin. Phys. B, 2016, 25 (11): 117401 doi: 10.1088/1674-1056/25/11/117401
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First-principles calculations by means of the full-potential linearized augmented plane wave method using the generalized gradient approximation with correlation effect correction (GGA+U) within the framework of spin polarized density functional theory (DFT+U) are used to study the structural, electronic, and magnetic properties of cubic perovskite compounds RbXF3 (X=Mn, V, Co, and Fe). It is found that the calculated structural parameters, i.e., lattice constant, bulk modulus, and its pressure derivative are in good agreement with the previous results. Our results reveal that the strong spin polarization of the 3d states of the X atoms is the origin of ferromagnetism in RbXF3. Cohesive energies and the magnetic moments of RbXF3 have also been calculated. The calculated electronic properties show the half-metallic nature of RbCoF3 and RbFeF3, making these materials suitable for spintronic applications.

Spatially resolved gap closing in single Josephson junctions constructed on Bi2Te3 surface Hot!

Yuan Pang(庞远), Junhua Wang(王骏华), Zhaozheng Lyu(吕昭征), Guang Yang(杨光), Jie Fan(樊洁), Guangtong Liu(刘广同), Zhongqing Ji(姬忠庆), Xiunian Jing(景秀年), Changli Yang(杨昌黎), Li Lu(吕力)
Chin. Phys. B, 2016, 25 (11): 117402 doi: 10.1088/1674-1056/25/11/117402
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Full gap closing is a prerequisite for hosting Majorana zero modes in Josephson junctions on the surface of topological insulators. Previously, we have observed direct experimental evidence of gap closing in Josephson junctions constructed on Bi2Te3 surface. In this paper we report further investigations on the position dependence of gap closing as a function of magnetic flux in single Josephson junctions constructed on Bi2Te3 surface.

Interplay between spin frustration and magnetism in the exactly solved two-leg mixed spin ladder

Yan Qi(齐岩), Song-Wei Lv(吕松玮), An Du(杜安), Nai-sen Yu(于乃森)
Chin. Phys. B, 2016, 25 (11): 117501 doi: 10.1088/1674-1056/25/11/117501
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We study a mixed spin-( 3/2, 1) ladder system with antiferromagnetic rung coupling and next-nearest-neighbor interaction. The exactly solved Ising-chain model is employed to investigate the ground-state properties and thermodynamics of the low-dimensional ladder system. Our results show that the competition between different exchange couplings brings in a large variety of ground states characterized by various values of normalized magnetization equal to 0, 1/5, 2/5, 3/5, 1. Moreover, an interesting double-peak structure is also detected in the thermal dependence of magnetic susceptibility and specific heat when the frustration comes into play. It is shown that the double-peak phenomenon at zero-field for the case of AF2 ground-state arises from the very strong antiferromagnetic rung coupling, while other cases are attributed to the excitations induced by temperature and external field around the phase boundary.

Size-dependent exchange bias in single phase Mn3O4 nanoparticles

Song-Wei Wang(王松伟), Xin Zhang(张鑫), Rong Yao(姚蓉), Guang-Hui Rao(饶光辉)
Chin. Phys. B, 2016, 25 (11): 117502 doi: 10.1088/1674-1056/25/11/117502
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Glassy magnetic behavior and exchange bias phenomena are observed in single phase Mn3O4 nanoparticles. Dynamics scaling analysis of the ac susceptibility and the Henkel plot indicate that the observed glassy behavior at low temperature can be understood by taking into account the intrinsic behavior of the individual particles consisting of a ferrimagnetic (FIM) core and a spin-glass surface layer. Field-cooled magnetization hysteresis loops display both horizontal and vertical shifts. Dependence of the exchange bias field (HE) on the cooling field shows an almost undamped feature up to 70 kOe, indicating the stable exchange bias state in Mn3O4.HE increases as the particle size decreases due to the higher surface/volume ratio. The occurrence of the exchange bias can be attributed to the pinning effect of the frozen spin-glass surface layer upon the FIM core.

Dy substitution effect on the temperature dependences of magnetostriction in Pr1-xDyxFe1.9 alloys

Yan-Mei Tang(唐妍梅), Hai-Fu Huang(黄海富), Shao-Long Tang(唐少龙), You-Wei Du(都有为)
Chin. Phys. B, 2016, 25 (11): 117503 doi: 10.1088/1674-1056/25/11/117503
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The temperature dependences of magnetostriction in Pr1-xDyxFe1.9 (0≤x≤1.0) alloys between 5 K and 300 K were investigated. An unusual decrease of magnetostriction with temperature decreasing was found in Pr-rich alloys (0≤x≤0.2), due to the change of the easy magnetization direction (EMD). Dy substitution reduces the magnetostriction in high-magnetic field (10 kOe≤H≤90 kOe) at 5 K, while a small amount of Dy substitution (x=0.05) is beneficial to increasing the magnetostriction in low-magnetic field between 10 K and 50 K. This makes the alloys a potential candidate for low temperature applications.

Improvement in coercivity,thermal stability,and corrosion resistance of sintered Nd-Fe-B magnets with Dy80Ga20 intergranular addition

Beibei Zhou(周贝贝), Xiangbin Li(李向斌), Xuejing Cao(曹学静), Gaolin Yan(严高林), Aru Yan(闫阿儒)
Chin. Phys. B, 2016, 25 (11): 117504 doi: 10.1088/1674-1056/25/11/117504
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To investigate the coercivity, corrosion resistance, and thermal stability of Nd-Fe-B magnets, their properties were investigated at room and high temperature before and after doping with Dy80Ga20 (at.%) powder. The coercivity of the magnets increased from the undoped value of 12.72 kOe to a doped value of 21.44 kOe. A micro-structural analysis indicates that a well-developed core-shell structure forms in the magnets doped with Dy80Ga20 powder. The improvement in magnetic properties is believed to be related to the refined and uniform matrix grains, continuous grain boundaries, and a hardened (Nd, Dy)2Fe14B shell surrounding the matrix grains. Additionally, the doped magnets exhibit an obvious improvement in thermal stability. For the magnets with added Dy80Ga20 powder, the temperature coefficients of remanence (α) and coercivity (β) increased to -0.106%℃-1 and -0.60%℃-1 over the range 20-100℃, compared to temperature coefficients of -0.117%℃-1 (α) and -0.74%℃-1 (β) in the regular magnets without Dy80Ga20 powder. The irreversible loss of magnetic flux (Hirr) was investigated at different temperatures. After being exposed to 150℃ for 2 h, the Hirr of magnets with 4 wt.% Dy80Ga20 decreased by ~95% compared to that of the undoped magnets. The enhanced temperature coefficients and Hirr indicate improved thermal stability in the doped Nd-Fe-B magnets. The intergranular addition of Dy80Ga20 also improved the corrosion resistance of the magnets because of the enhanced intergranular phase. In a corrosive atmosphere for 96 h, the mass loss of the sintered magnets with 4 wt.% Dy80Ga20 was 2.68 mg/cm2, less than 10% of that suffered by the undoped magnets (28.1 mg/cm2).

Lumped modeling with circuit elements for nonreciprocal magnetoelectric tunable band-pass filter

Xiao-Hong Li(李小红), Hao-Miao Zhou(周浩淼), Qiu-shi Zhang(张秋实), Wen-Wen Hu(胡文文)
Chin. Phys. B, 2016, 25 (11): 117505 doi: 10.1088/1674-1056/25/11/117505
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This paper presents a lumped equivalent circuit model of the nonreciprocal magnetoelectric tunable microwave band-pass filter. The reciprocal coupled-line circuit is based on the converse magnetoelectric effect of magnetoelectric composites, includes the electrical tunable equivalent factor of the piezoelectric layer, and is established by the introduced lumped elements, such as radiation capacitance, radiation inductance, and coupling inductance, according to the transmission characteristics of the electromagnetic wave and magnetostatic wave in an inverted-L-shaped microstrip line and ferrite slab. The nonreciprocal transmission property of the filter is described by the introduced T-shaped circuit containing controlled sources. Finally, the lumped equivalent circuit of a nonreciprocal magnetoelectric tunable microwave band-pass filter is given and the lumped parameters are also expressed. When the deviation angles of the ferrite slab are respectively 0° and 45°, the corresponding magnetoelectric devices are respectively a reciprocal device and a nonreciprocal device. The curves of S parameter obtained by the lumped equivalent circuit model and electromagnetic simulation are in good agreement with the experimental results. When the deviation angle is between 0° and 45°, the maximum value of the S parameter predicted by the lumped equivalent circuit model is in good agreement with the experimental result. The comparison results of the paper show that the lumped equivalent circuit model is valid. Further, the effect of some key material parameters on the performance of devices is predicted by the lumped equivalent circuit model. The research can provide the theoretical basis for the design and application of nonreciprocal magnetoelectric tunable devices.

Effects of thickness and annealing condition on magnetic properties and thermal stabilities of Ta/Nd/NdFeB/Nd/Ta sandwiched films

Wen-Feng Liu(刘文峰), Min-Gang Zhang(张敏刚), Ke-Wei Zhang(张克维), Hai-Jie Zhang(张海杰), Xiao-Hong Xu(许小红), Yue-Sheng Chai(柴跃生)
Chin. Phys. B, 2016, 25 (11): 117506 doi: 10.1088/1674-1056/25/11/117506
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Ta/Nd/NdFeB/Nd/Ta sandwiched films are deposited by magnetron sputtering on Si (100) substrates, and subsequently annealed in vacuum at different temperatures for different time. It is found that both the thickness of NdFeB and Nd layer and the annealing condition can affect the magnetic properties of Ta/Nd/NdFeB/Nd/Ta films. Interestingly, the thickness and annealing temperature show the relevant behaviors that can affect the magnetic properties of the film. The high coercivity of 24.1 kOe (1 Oe=79.5775 A/m) and remanence ratio (remanent magnetization/saturation magnetization) of 0.94 can be obtained in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed for 3 min at 1023 K. In addition, the thermal stability of the film is also linked to the thickness of NdFeB and Nd layer and the annealing temperature as well. The excellent thermal stability can be achieved in a Ta/Nd(250 nm)/NdFeB(600 nm)/Nd(250 nm)/Ta film annealed at 1023 K.

Threshold resistance switching in silicon-rich SiOx thin films

Da Chen(陈达), Shi-Hua Huang(黄仕华)
Chin. Phys. B, 2016, 25 (11): 117701 doi: 10.1088/1674-1056/25/11/117701
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Si-rich SiOx and amorphous Si clusters embedded in SiOx films were prepared by the radio-frequency magnetron cosputtering method and high-temperature annealing treatment. The threshold resistance switching behavior was achieved from the memory mode by continuous bias sweeping in all films, which was caused by the formation of clusters due to the local overheating under a large electric field. Besides, the I-V characteristics of the threshold switching showed a dependence on the annealing temperature and the SiOx thickness. In particular, formation and rupture of conduction paths is considered to be the switching mechanism for the 39 nm-SiOx film, while for the 78 nm-SiOx film, adjusting of the Schottky barrier height between insulator and semiconductor is more reasonable. This study demonstrates the importance of investigation of both switching modes in resistance random access memory.

Exchange effect and magneto-plasmon mode dispersion in an anisotropic two-dimensional electronic system

Xiaoguang Wu(吴晓光)
Chin. Phys. B, 2016, 25 (11): 117801 doi: 10.1088/1674-1056/25/11/117801
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The exchange effect and the magneto-plasmon mode dispersion are studied theoretically for an anisotropic two-dimensional electronic system in the presence of a uniform perpendicular magnetic field. Employing an effective low-energy model with anisotropic effective masses, which is relevant for a monolayer of phosphorus, the exchange effect due to the electron-electron interaction is treated within the self-consistent Hartree-Fock approximation. The magneto-plasmon mode dispersion is obtained by solving a Bethe-Salpeter equation for the electron density-density correlation function within the ladder diagram approximation. It is found that the exchange effect is reduced in the anisotropic system in comparison with the isotropic one. The magneto-plasmon mode dispersion shows a clear dependence on the direction of the wave vector.

Full-profile fitting of emission spectrum to determine transition intensity parameters of Yb3+: GdTaO4

Qingli Zhang(张庆礼), Guihua Sun(孙贵花), Kaijie Ning(宁凯杰), Chaoshu Shi(施朝淑), Wenpeng Liu(刘文鹏), Dunlu Sun(孙敦陆), Shaotang Yin(殷绍唐)
Chin. Phys. B, 2016, 25 (11): 117802 doi: 10.1088/1674-1056/25/11/117802
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The Judd-Ofelt theoretic transition intensity parameters Atpk of luminescence of rare-earth ions in solids are important for the quantitative analysis of luminescence. It is very difficult to determine them with emission or absorption spectra for a long time. A “full profile fitting” method to obtain Atpk in solids with its emission spectrum is proposed, in which the contribution of a radiative transition to the emission spectrum is expressed as the product of transition probability, line profile function, instrument measurement constant and transition center frequency or wavelength, and the whole experimental emission spectrum is the sum of all transitions. In this way, the emission spectrum is expressed as a function with the independent variables intensity parameters Atpk, full width at half maximum (FWHM) of profile functions, instrument measurement constant, wavelength, and the Huang-Rhys factor S if the lattice vibronic peaks in the emission spectrum should be considered. The ratios of the experimental to the calculated energy lifetimes are incorporated into the fitting function to remove the arbitrariness during fitting Atpk and other parameters. Employing this method obviates measurement of the absolute emission spectrum intensity. It also eliminates dependence upon the number of emission transition peaks. Every experiment point in emission spectra, which usually have at least hundreds of data points, is the function with variables Atpk and other parameters, so it is usually viable to determine Atpk and other parameters using a large number of experimental values. We applied this method to determine twenty-five Atpk of Yb3+ in GdTaO4. The calculated and experiment energy lifetimes, experimental and calculated emission spectrum are very consistent, indicating that it is viable to obtain the transition intensity parameters of rare-earth ions in solids by a full profile fitting to the ions' emission spectrum. The calculated emission cross sections of Yb3+:GdTaO4 also indicate that the F-L formula gives larger values in the wavelength range with reabsorption.

Engineering optical gradient force from coupled surface plasmon polariton modes in nanoscale plasmonic waveguides

Jiahui Lu(卢佳慧), Guanghui Wang(王光辉)
Chin. Phys. B, 2016, 25 (11): 117804 doi: 10.1088/1674-1056/25/11/117804
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We explore the dispersion properties and optical gradient forces from mutual coupling of surface plasmon polariton (SPP) modes at two interfaces of nanoscale plasmonic waveguides with hyperbolic metamaterial cladding. With Maxwell's equations and Maxwell stress tensor, we calculate and compare the dispersion relation and optical gradient force for symmetric and antisymmetric SPP modes in two kinds of nanoscale plasmonic waveguides. The numerical results show that the optical gradient force between two coupled hyperbolic metamaterial waveguides can be engineered flexibly by adjusting the waveguide structure parameters. Importantly, an alternative way to boost the optical gradient force is provided through engineering the hyperbolic metamaterial cladding of suitable orientation. These special optical properties will open the door for potential optomechanical applications, such as optical tweezers and actuators.

Effect of Mo capping layers thickness on the perpendicular magnetic anisotropy in MgO/CoFeB based top magnetic tunnel junction structure

Yi Liu(刘毅), Kai-Gui Zhu(朱开贵), Hui-Cai Zhong(钟汇才), Zheng-Yong Zhu(朱正勇), Tao Yu(于涛), Su-De Ma(马苏德)
Chin. Phys. B, 2016, 25 (11): 117805 doi: 10.1088/1674-1056/25/11/117805
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A detailed study of the magnetic characterizations of the top structure MgO/CoFeB/Mo is presented. The samples show strong perpendicular magnetic anisotropy (PMA) when the thickness of CoFeB is 0.9 nm and 1.1 nm. The saturation magnetic moment and interface anisotropy constant are 1566 emu/cm3 and 3.75 erg/cm2, respectively. The magnetic dead layer (MDL) is about 0.23 nm in this system. Furthermore, strong capping layer thickness dependence is also observed. The strong PMA of 1.1 nm CoFeB only exists in a Mo cap layer thickness window of 1.2-2 nm. To maintain PMA, the metal layer could not be too thin or thick in these multilayers. The oxidation and diffusion of the metal capping layer should be respectively responsibility for the degradation of PMA in these thin or thick metal capping layer samples.

Restructuring of plasmonic nanoparticle aggregates with arbitrary particle size distribution in pulsed laser fields

A E Ershov, A P Gavrilyuk, S V Karpov, S P Polyutov
Chin. Phys. B, 2016, 25 (11): 117806 doi: 10.1088/1674-1056/25/11/117806
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We have studied processes of interaction of pulsed laser radiation with resonant groups of plasmonic nanoparticles (resonant domains) in large colloidal nanoparticle aggregates having different interparticle gaps and particle size distributions. These processes are responsible for the origin of nonlinear optical effects and photochromic reactions in multiparticle aggregates. To describe photo-induced transformations in resonant domains and alterations in their absorption spectra remaining after the pulse action, we introduce the factor of spectral photomodification. Based on calculation of changes in thermodynamic, mechanical, and optical characteristics of the domains, the histograms of the spectrum photomodification factor have been obtained for various interparticle gaps, an average particle size, and the degree of polydispersity. Variations in spectra have been analyzed depending on the intensity of laser radiation and various combinations of size characteristics of domains. The obtained results can be used to predict manifestation of photochromic effects in composite materials containing different plasmonic nanoparticle aggregates in pulsed laser fields.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY

Low specific contact resistivity to graphene achieved by AuGe/Ni/Au and annealing process

Shu-Zhen Yu(于淑珍), Yan Song(宋焱), Jian-Rong Dong(董建荣), Yu-Run Sun(孙玉润), Yong-Ming Zhao(赵勇明), Yang He(何洋)
Chin. Phys. B, 2016, 25 (11): 118101 doi: 10.1088/1674-1056/25/11/118101
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Low metal-graphene contact resistance is important in making high-performance graphene devices. In this work, we demonstrate a lower specific contact resistivity of Au0.88 Ge0.12/Ni/Au-graphene contact compared with Ti/Au and Ti/Pt/Au contacts. The rapid thermal annealing process was optimized to improve AuGe/Ni/Au contact resistance. Results reveal that both pre- and post-annealing processes are effective for reducing the contact resistance. The specific contact resistivity decreases from 2.5×10-4 to 7.8×10-5 Ω·cm2 by pre-annealing at 300℃ for one hour, and continues to decrease to 9.5×10-7 Ω·cm2 after post-annealing at 490℃ for 60 seconds. These approaches provide reliable means of lowering contact resistance.

Metal-enhanced fluorescence of graphene oxide by palladium nanoparticles in the blue-green part of the spectrum

A Omidvar, M R RashidianVaziri, B Jaleh, N Partovi Shabestari, M Noroozi
Chin. Phys. B, 2016, 25 (11): 118102 doi: 10.1088/1674-1056/25/11/118102
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Graphene oxide (GO) has a wide fluorescence bandwidth, which makes it a prospective candidate for numerous applications. For many of these applications, the fluorescence yield of GO should be further increased. The sp2-hybridized carbons in GO confine the π-electrons. Radiative recombination of electron-hole pairs in such sp2 clusters is the source of fluorescence in this material. Palladium nanoparticles are good catalysts for sp2 bond formations. We report on the preparation of GO, palladium nanoparticles and their nanocomposites in two different solvents. It is shown that palladium nanoparticles can considerably enhance the intrinsic fluorescence of GO in the blue-green part of the visible light spectrum. Fluorescence enhancement has been attributed to the catalytic role of palladium nanoparticles in increasing the number of sp2 bonds of GO with the molecules of the surrounding media. It is shown that palladium nanoparticles could be the nanoparticle of choice for fluorescence enhancement of GO because of their catalytic role in sp2 bond formation.

Bolometric effect in a waveguide-integrated graphene photodetector

Yubing Wang(王玉冰), Weihong Yin(尹伟红), Qin Han(韩勤), Xiaohong Yang(杨晓红), Han Ye(叶焓), Qianqian Lv(吕倩倩), Dongdong Yin(尹冬冬)
Chin. Phys. B, 2016, 25 (11): 118103 doi: 10.1088/1674-1056/25/11/118103
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Graphene is an alternative material for photodetectors owing to its unique properties. These include its uniform absorption of light from ultraviolet to infrared and its ultrahigh mobility for both electrons and holes. Unfortunately, due to the low absorption of light, the photoresponsivity of graphene-based photodetectors is usually low, only a few milliamps per watt. In this letter, we fabricate a waveguide-integrated graphene photodetector. A photoresponsivity exceeding 0.11 A·W-1 is obtained which enables most optoelectronic applications. The dominating mechanism of photoresponse is investigated and is attributed to the photo-induced bolometric effect. Theoretical calculation shows that the bolometric photoresponsivity is 4.6 A·W-1. The absorption coefficient of the device is estimated to be 0.27 dB·μ-1.

Large single crystal diamond grown in FeNiMnCo-S-C system under high pressure and high temperature conditions

He Zhang(张贺), Shangsheng Li(李尚升), Taichao Su(宿太超), Meihua Hu(胡美华), Guanghui Li(李光辉), Hongan Ma(马红安), Xiaopeng Jia(贾晓鹏)
Chin. Phys. B, 2016, 25 (11): 118104 doi: 10.1088/1674-1056/25/11/118104
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Large diamonds have successfully been synthesized from FeNiMnCo-S-C system at temperatures of 1255-1393 ° C and pressures of 5.3-5.5 GPa. Because of the presence of sulfur additive, the morphology and color of the large diamond crystals change obviously. The content and shape of inclusions change with increasing sulfur additive. It is found that the pressure and temperature conditions required for the synthesis decrease to some extent with the increase of S additive, which results in left down of the V-shape region. The Raman spectra show that the introduction of additive sulfur reduces the quality of the large diamond crystals. The x-ray photoelectron spectroscopy (XPS) spectra show the presence of S in the diamonds. Furthermore, the electrical properties of the large diamond crystals are tested by a four-point probe and the Hall effect method. When sulfur in the cell of diamond is up to 4.0 wt.%, the resistance of the diamond is 9.628×105 Ω·cm. It is shown that the large single crystal samples are n type semiconductors. This work is helpful for the further research and application of sulfur-doped semiconductor large diamond.

Large scale fabrication of nitrogen vacancy-embedded diamond nanostructures for single-photon source applications Hot!

Qianqing Jiang(姜倩晴), Wuxia Li(李无瑕), Chengchun Tang(唐成春), Yanchun Chang(常彦春), Tingting Hao(郝婷婷), Xinyu Pan(潘新宇), Haitao Ye(叶海涛), Junjie Li(李俊杰), Changzhi Gu(顾长志)
Chin. Phys. B, 2016, 25 (11): 118105 doi: 10.1088/1674-1056/25/11/118105
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Color centers in diamond are prominent candidates for generating and manipulating quantum states of light, even at room temperature. However, the photon collection efficiency of bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, we fabricated arrays of diamond nanostructures, differing in both diameter and top end shape, with HSQ, PMMA, and Cr as the etching mask materials, aiming toward large scale fabrication of single-photon sources with enhanced collection efficiency made of nitrogen vacancy (NV) embedded diamond. With a mixture of O2 and CHF3 gas plasma, diamond pillars with diameters down to 45 nm were obtained. The top end shape evolution has been represented with a simple model. The tests of size dependent single-photon properties confirmed an improved single-photon collection efficiency enhancement, larger than tenfold, and a mild decrease of decoherence time with decreasing pillar diameter was observed as expected. These results provide useful information for future applications of nanostructured diamond as a single-photon source.

High performance photodetectors based on high quality InP nanowires Hot!

Yan-Kun Yang(杨燕琨), Tie-Feng Yang(杨铁锋), Hong-Lai Li(李洪来), Zhao-Yang Qi(祁朝阳), Xin-Liang Chen(陈新亮), Wen-Qiang Wu(吴文强), Xue-Lu Hu(胡学鹿), Peng-Bin He(贺鹏斌), Ying Jiang(蒋英), Wei Hu(胡伟), Qing-Lin Zhang(张清林), Xiu-Juan Zhuang(庄秀娟), Xiao-Li Zhu(朱小莉), An-Lian Pan(潘安练)
Chin. Phys. B, 2016, 25 (11): 118106 doi: 10.1088/1674-1056/25/11/118106
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In this paper, small diameter InP nanowires with high crystal quality were synthesized through a chemical vapor deposition method. Benefitting from the high crystallinity and large specific surface area of InP nanowires, the simply constructed photodetector demonstrates a high responsivity of up to 1170 A·W-1 and an external quantum efficiency of 2.8×105% with a fast rise time of 110 ms and a fall time of 130 ms, even at low bias of 0.1 V. The effect of back-gate voltage on photoresponse of the device was systematically investigated, confirming that the photocurrent dominates over thermionic and tunneling currents in the whole operation. A mechanism based on energy band theory at the junction between metal and semiconductor was proposed to explain the back-gate voltage dependent performance of the photodetectors. These convincing results indicate that fine InP nanowires will have a brilliant future in smart optoelectronics.

Block copolymer morphologies confined by square-shaped particle: Hard and soft confinement

Qiyi Zhang(张启义), Wenyan Yang(杨文艳), Kaiyan Hu(胡凯燕)
Chin. Phys. B, 2016, 25 (11): 118201 doi: 10.1088/1674-1056/25/11/118201
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The self-assembly of diblock copolymers confined around one square-shaped particle is studied systematically within two-dimensional self-consistent field theory (SCFT). In this model, we assume that the thin block copolymer film is confined in the vicinity of a square-shaped particle by a homopolymer melt, which is equivalent to the poor solvents. Multiple sequences of square-shaped particle-induced copolymer aggregates with different shapes and self-assembled internal morphologies are predicted as functions of the particle size, the structural portion of the copolymer, and the volume fraction of the copolymer. A rich variety of aggregates are found with complex internal self-assembled morphologies including complex structures of the vesicle, with one or several inverted micelle surrounded by the outer monolayer with the particle confined in the core. These results demonstrate that the assemblies of diblock copolymers formed around the square-shaped particle in poor solvents are of immediate interest to the assembly of copolymer and the morphology of biomembrane in the confined environment, as well as to the transitions of vesicles to micelles.

Polydisperse spherical colloidal silica particles: Preparation and application

Hui Kong(孔慧), Junchao Huo(霍军朝), Chenliang Liang(梁晨亮), Shasha Li(李沙沙), Weili Liu(刘卫丽), Zhitang Song(宋志棠)
Chin. Phys. B, 2016, 25 (11): 118202 doi: 10.1088/1674-1056/25/11/118202
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A new industrial method has been developed to produce polydisperse spherical colloidal silica particles with a very broad particle size, ranging from 20-95 nm. The process uses a reactor in which the original seed solution is heated to 100 ° C, and then active silicic acid and the seed solution are titrated to the reactor continuously with a constant rate. The original seeds and the titrated seeds in the reactor will go through different particle growth cycles to form different particle sizes. Both the particles' size distribution and morphology have been characterized by dynamic light scattering (DLS) and the focus ion beam (FIB) system. In addition, the as-prepared polydisperse colloidal silica particle in the application of sapphire wafer's chemical mechanical polishing (CMP) process has been tested. The material removal rate (MRR) of this kind of abrasive has been tested and verified to be much faster than traditional monodisperse silica particles. Finally, the mechanism of sapphire CMP process by this kind of polydisperse silica particles has been investigated to explore the reasons for the high polishing rate.

Parasitic effects of air-gap through-silicon vias in high-speed three-dimensional integrated circuits

Xiaoxian Liu(刘晓贤), Zhangming Zhu(朱樟明), Yintang Yang(杨银堂), Ruixue Ding(丁瑞雪), Yuejin Li(李跃进)
Chin. Phys. B, 2016, 25 (11): 118401 doi: 10.1088/1674-1056/25/11/118401
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In this paper, ground-signal-ground type through-silicon vias (TSVs) exploiting air gaps as insulation layers are designed, analyzed and simulated for applications in millimeter wave. The compact wideband equivalent-circuit model and passive elements (RLGC) parameters based on the physical parameters are presented with the frequency up to 100 GHz. The parasitic capacitance of TSVs can be approximated as the dielectric capacitance of air gaps when the thickness of air gaps is greater than 0.75 μm. Therefore, the applied voltage of TSVs only needs to achieve the flatband voltage, and there is no need to indicate the threshold voltage. This is due to the small permittivity of air gaps. The proposed model shows good agreement with the simulation results of ADS and Ansoft's HFSS over a wide frequency range.

An ultra-wideband pattern reconfigurable antenna based on graphene coating

YanNan Jiang(姜彦南), Rui Yuan(袁锐), Xi Gao(高喜), Jiao Wang(王娇), SiMin Li(李思敏), Yi-Yu Lin(林诒玉)
Chin. Phys. B, 2016, 25 (11): 118402 doi: 10.1088/1674-1056/25/11/118402
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An ultra-wideband pattern reconfigurable antenna is proposed. The antenna is a dielectric coaxial hollow monopole with a cylindrical graphene-based impedance surface coating. It consists of a graphene sheet coated onto the inner surface of a cylindrical substrate and a set of independent polysilicon DC gating pads mounted on the outside of the cylindrical substrate. By changing the DC bias voltages to the different gating pads, the surface impedance of the graphene coating can be freely controlled. Due to the tunability of graphene's surface impedance, the radiation pattern of the proposed antenna can be reconfigured. A transmission line method is used to illustrate the physical mechanism of the proposed antenna. The results show that the proposed antenna can reconfigure its radiation pattern in the omnidirectional mode with the relative bandwidth of 58.5% and the directional mode over the entire azimuth plane with the relative bandwidth of 67%.

Theoretical investigation of frequency characteristics of free oscillation and injection-locked magnetrons

Song Yue(岳松), Dong-ping Gao(高冬平), Zhao-chuan Zhang(张兆传), Wei-long Wang(王韦龙)
Chin. Phys. B, 2016, 25 (11): 118403 doi: 10.1088/1674-1056/25/11/118403
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The frequency characteristics of free oscillation magnetron (FOM) and injection-locked magnetron (ILM) are theoretically investigated. By using the equal power voltage obtained from the experiment data, expressions of the frequency and radio frequency (RF) voltage of FOM and ILM, as well as the locking bandwidth, on the anode voltage and magnetic field are derived. With the increase of the anode voltage and the decrease of the magnetic field, the power and its growth rate increase, while the frequency increases and its growth rate decreases. The theoretical frequency and power of FOM agree with the particle-in-cell (PIC) simulation results. Besides, the theoretical trends of the power and frequency with the anode voltage and magnetic field are consistent with the experimental results, which verifies the accuracy of the theory. The theory provides a novel calculation method of frequency characteristics. It can approximately analyze the power and frequency of both FOM and ILM, which promotes the industrial applications of magnetron and microwave energy.

Analytical threshold voltage model for strained silicon GAA-TFET

Hai-Yan Kang(康海燕), Hui-Yong Hu(胡辉勇), Bin Wang(王斌)
Chin. Phys. B, 2016, 25 (11): 118501 doi: 10.1088/1674-1056/25/11/118501
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Tunnel field effect transistors (TFETs) are promising devices for low power applications. An analytical threshold voltage model, based on the channel surface potential and electric field obtained by solving the 2D Poisson's equation, for strained silicon gate all around TFETs is proposed. The variation of the threshold voltage with device parameters, such as the strain (Ge mole fraction x), gate oxide thickness, gate oxide permittivity, and channel length has also been investigated. The threshold voltage model is extracted using the peak transconductance method and is verified by good agreement with the results obtained from the TCAD simulation.

Equivalent distributed capacitance model of oxide traps onfrequency dispersion of C-V curve for MOS capacitors

Han-Han Lu(卢汉汉), Jing-Ping Xu(徐静平), Lu Liu(刘璐), Pui-To Lai(黎沛涛), Wing-Man Tang(邓咏雯)
Chin. Phys. B, 2016, 25 (11): 118502 doi: 10.1088/1674-1056/25/11/118502
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An equivalent distributed capacitance model is established by considering only the gate oxide-trap capacitance to explain the frequency dispersion in the C-V curve of MOS capacitors measured for a frequency range from 1 kHz to 1 MHz. The proposed model is based on the Fermi-Dirac statistics and the charging/discharging effects of the oxide traps induced by a small ac signal. The validity of the proposed model is confirmed by the good agreement between the simulated results and experimental data. Simulations indicate that the capacitance dispersion of an MOS capacitor under accumulation and near flatband is mainly caused by traps adjacent to the oxide/semiconductor interface, with negligible effects from the traps far from the interface, and the relevant distance from the interface at which the traps can still contribute to the gate capacitance is also discussed. In addition, by excluding the negligible effect of oxide-trap conductance, the model avoids the use of imaginary numbers and complex calculations, and thus is simple and intuitive.

Ultra-low temperature radio-frequency performance of partially depleted silicon-on-insulator n-type metal-oxide-semiconductor field-effect transistors with tunnel diode body contact structures

Kai Lu(吕凯), Jing Chen(陈静), Yuping Huang(黄瑜萍), Jun Liu(刘军), Jiexin Luo(罗杰馨), Xi Wang(王曦)
Chin. Phys. B, 2016, 25 (11): 118503 doi: 10.1088/1674-1056/25/11/118503
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Radio-frequency (RF) characteristics under ultra-low temperature of multi-finger partially depleted silicon-on-insulator (PD SOI) n-type metal-oxide-semiconductor field-effect transistors (nMOSFETs) with tunnel diode body-contact (TDBC) structure and T-gate body-contact (TB) structure are investigated in this paper. When operating at 77 K, TDBC device suppresses floating-body effect (FBE) as well as the TB device. For TB device and TDBC device, cut-off frequency (fT) improves as the temperature decreases to liquid-helium temperature (77 K) while that of the maximum oscillation frequency (fMAX) is opposite due to the decrease of the unilateral power gain. While operating under 77 K, fT and fMAX of TDBC device reach to 125 GHz and 77 GHz, representing 8% and 15% improvements compared with those of TB device, respectively, which is mainly due to the lower parasitic resistances and capacitances. The results indicate that TDBC SOI MOSFETs could be considered as promising candidates for analog and RF applications over a wide range of temperatures and there is immense potential for the development of RF CMOS integrated circuits for cryogenic applications.

Technology demonstration of a novel poly-Si nanowire thin film transistor

Libin Liu(刘立滨), Renrong Liang(梁仁荣), Bolin Shan(单柏霖), Jun Xu(许军), Jing Wang(王敬)
Chin. Phys. B, 2016, 25 (11): 118504 doi: 10.1088/1674-1056/25/11/118504
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A simple process flow method for the fabrication of poly-Si nanowire thin film transistors (NW-TFTs) without advanced lithographic tools is introduced in this paper. The cross section of the nanowire channel was manipulated to have a parallelogram shape by combining a two-step etching process and a spacer formation technique. The electrical and temperature characteristics of the developed NW-TFTs are measured in detail and compared with those of conventional planar TFTs (used as a control). The as-demonstrated NW-TFT exhibits a small subthreshold swing (191 mV/dec), a high ON/OFF ratio (8.5×107), a low threshold voltage (1.12 V), a decreased OFF-state current, and a low drain-induced-barrier lowering value (70.11 mV/V). The effective trap densities both at the interface and grain boundaries are also significantly reduced in the NW-TFT. The results show that all improvements of the NW-TFT originate from the enhanced gate controllability of the multi-gate over the channel.

Bias-dependent timing jitter of 1-GHz sinusoidally gated InGaAs/InP avalanche photodiode

Ge Zhu(朱阁), Fu Zheng(郑福), Chao Wang(王超), Zhibin Sun(孙志斌), Guangjie Zhai(翟光杰), Qing Zhao(赵清)
Chin. Phys. B, 2016, 25 (11): 118505 doi: 10.1088/1674-1056/25/11/118505
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We characterized the dependence of the timing jitter of an InGaAs/InP single-photon avalanche diode on the excess bias voltage (Vex) when operated in 1-GHz sinusoidally gated mode. The single-photon avalanche diode was cooled to -30 degrees Celsius. When the Vex is too low (0.2 V-0.8 V) or too high (3 V-4.2 V), the timing jitter is increased with the Vex, particularly at high Vex. While at middle Vex (1 V-2.8 V), the timing jitter is reduced. Measurements of the timing jitter of the same avalanche diode with pulsed gating show that this effect is likely related to the increase of both the amplitude of the Vex and the width of the gate-on time. For the 1-GHz sinusoidally gated detector, the best jitter of 93 ps is achieved with a photon detection efficiency of 21.4% and a dark count rate of ~2.08×10-5 per gate at the Vex of 2.8 V. To evaluate the whole performance of the detector, we calculated the noise equivalent power (NEP) and the afterpulse probability (Pap). It is found that both NEP and Pap increase quickly when the Vex is above 2.8 V. At 2.8-V Vex, the NEP and Pap are ~2.06×10-16 W/Hz1/2 and 7.11%, respectively. Therefore, the detector should be operated with Vex of 2.8 V to exploit the fast time response, low NEP and low Pap.

High-performance InGaN/GaN MQW LEDs with Al-doped ZnO transparent conductive layers grown by MOCVD using H2O as an oxidizer

Jia-Yong Lin(林家勇), Yan-Li Pei(裴艳丽), Yi Zhuo(卓毅), Zi-Min Chen(陈梓敏), Rui-Qin Hu(胡锐钦), Guang-Shuo Cai(蔡广烁), Gang Wang(王钢)
Chin. Phys. B, 2016, 25 (11): 118506 doi: 10.1088/1674-1056/25/11/118506
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In this study, the high performance of InGaN/GaN multiple quantum well light-emitting diodes (LEDs) with Al-doped ZnO (AZO) transparent conductive layers (TCLs) has been demonstrated. The AZO-TCLs were fabricated on the n+-InGaN contact layer by metal organic chemical vapor deposition (MOCVD) using H2O as an oxidizer at temperatures as low as 400℃ without any post-deposition annealing. It shows a high transparency (98%), low resistivity (510-4 Ω·cm), and an epitaxial-like excellent interface on p-GaN with an n+-InGaN contact layer. A forward voltage of 2.82 V@20 mA was obtained. Most importantly, the power efficiencies can be markedly improved by 53.8%@20 mA current injection and 39.6%@350 mA current injection compared with conventional LEDs with indium tin oxide TCL (LED-Ⅲ), and by 28.8%@20 mA current injection and 4.92%@350 mA current injection compared with LEDs with AZO-TCL prepared by MOCVD using O2 as an oxidizer (LED-Ⅱ), respectively. The results indicate that the AZO-TCL grown by MOCVD using H2O as an oxidizer is a promising TCL for a low-cost and high-efficiency GaN-based LED application.

Dynamic instability of collective myosin II motors

Jin-Fang Li(李金芳), Zi-Qing Wang(汪自庆), Qi-Kun Li(李奇昆), Jian-Jun Xing(邢建军), Guo-Dong Wang(王国栋)
Chin. Phys. B, 2016, 25 (11): 118701 doi: 10.1088/1674-1056/25/11/118701
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Some kinds of muscles can oscillate spontaneously, which is related to the dynamic instability of the collective motors. Based on the two-state ratchet model and with consideration of the motor stiffness, the dynamics of collective myosin Ⅱ motors are studied. It is shown that when the motor stiffness is small, the velocity of the collective motors decreases monotonically with load increasing. When the motor stiffness becomes large, dynamic instability appears in the force-velocity relationship of the collective-motor transport. For a large enough motor stiffness, the zero-velocity point lies in the unstable range of the force-velocity curve, and the motor system becomes unstable before the motion is stopped, so spontaneous oscillations can be generated if the system is elastically coupled to its environment via a spring. The oscillation frequency is related to the motor stiffness, motor binding rate, spring stiffness, and the width of the ATP excitation interval. For a medium motor stiffness, the zero-velocity point lies outside the unstable range of the force-velocity curve, and the motion will be stopped before the instability occurs.

Control of epitaxial growth at a-Si: H/c-Si heterointerface by the working pressure in PECVD

Yanjiao Shen(沈艳娇), Jianhui Chen(陈剑辉), Jing Yang(杨静), Bingbing Chen(陈兵兵), Jingwei Chen(陈静伟), Feng Li(李峰), Xiuhong Dai(代秀红), Haixu Liu(刘海旭), Ying Xu(许颖), Yaohua Mai(麦耀华)
Chin. Phys. B, 2016, 25 (11): 118801 doi: 10.1088/1674-1056/25/11/118801
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The epitaxial-Si (epi-Si) growth on the crystalline Si (c-Si) wafer could be tailored by the working pressure in plasma-enhanced chemical vapor deposition (PECVD). It has been systematically confirmed that the epitaxial growth at the hydrogenated amorphous silicon (a-Si:H)/c-Si interface is suppressed at high pressure (hp) and occurs at low pressure (lp). The hp a-Si:H, as a purely amorphous layer, is incorporated in the lp-epi-Si/c-Si interface. We find that:(i) the epitaxial growth can also occur at a-Si:H coated c-Si wafer as long as this amorphous layer is thin enough; (ii) with the increase of the inserted hp layer thickness, lp epi-Si at the interface is suppressed, and the fraction of a-Si:H in the thin films increases and that of c-Si decreases, corresponding to the increasing minority carrier lifetime of the sample. Not only the epitaxial results, but also the quality of the thin films at hp also surpasses that at lp, leading to the longer minority carrier lifetime of the hp sample than the lp one although they have the same amorphous phase.

Pedestrians' behavior in emergency evacuation: Modeling and simulation

Lei Wang(汪蕾), Jie-Hui Zheng(郑杰慧), Xiao-Shuang Zhang(张晓爽), Jian-Lin Zhang(张建林), Qiu-Zhen Wang(王求真), Qian Zhang(张茜)
Chin. Phys. B, 2016, 25 (11): 118901 doi: 10.1088/1674-1056/25/11/118901
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The social force model has been widely used to simulate pedestrian evacuation by analyzing attractive, repulsive, driving, and fluctuating forces among pedestrians. Many researchers have improved its limitations in simulating behaviors of large-scale population. This study modifies the well-accepted social force model by considering the impacts of interaction among companions and further develops a comprehensive model by combining that with a multi-exit utility function. Then numerical simulations of evacuations based on the comprehensive model are implemented in the waiting hall of the Wulin Square Subway Station in Hangzhou, China. The results provide safety thresholds of pedestrian density and panic levels in different operation situations. In spite of the operation situation and the panic level, a larger friend-group size results in lower evacuation efficiency. Our study makes important contributions to building a comprehensive multi-exit social force model and to applying it to actual scenarios, which produces data to facilitate decision making in contingency plans and emergency treatment.
GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS

North west cape-induced electron precipitation and theoretical simulation

Zhen-xia Zhang(张振霞), Xin-qiao Li(李新乔), Chen-Yu Wang(王辰宇), Lun-Jin Chen
Chin. Phys. B, 2016, 25 (11): 119401 doi: 10.1088/1674-1056/25/11/119401
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Enhancement of the electron fluxes in the inner radiation belt, which is induced by the powerful North West Cape (NWC) very-low-frequency (VLF) transmitter, have been observed and analyzed by several research groups. However, all of the previous publications have focused on NWC-induced >100-keV electrons only, based on observations from the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and the Geostationary Operational Environmental Satellite (GOES) satellites. Here, we present flux enhancements with 30-100-keV electrons related to NWC transmitter for the first time, which were observed by the GOES satellite at night. Similar to the 100-300-keV precipitated-electron behavior, the low energy 30-100-keV electron precipitation is primarily located east of the transmitter. However, the latter does not drift eastward to the same extent as the former, possibly because of the lower electron velocity. The 30-100-keV electrons are distributed in the L=1.8-2.1 L-shell range, in contrast to the 100-300-keV electrons which are at L=1.67-1.9. This is consistent with the perspective that the energy of the VLF-wave-induced electron flux enhancement decreases with higher L-shell values. We expand upon the rationality of the simultaneous enhancement of the 30-100- and 100-300-keV electron fluxes through comparison with the cyclotron resonance theory for the quasi-linear wave-particle interaction. In addition, we interpret the asymmetry characteristics of NWC electric power distribution in north and south hemisphere by ray tracing model. Finally, we present considerable discussion and show that good agreement exists between the observation of satellites and theory.
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