贝利相与非线性输运

电子输运现象包含一系列很重要的材料性质,并可以用来提供关于载体物理系统的很多信息。在 最近的二三十年,人们逐渐认识到除了电子能谱之外,电子在布里渊区的几何性质,比如贝利曲率和 轨道磁矩,会在电子输运中起到关键性的作用。在线性输运现象中的此种关联已引起广泛的兴趣并得 到深入的研究。然而,在非线性输运现象中的电子几何性质的作用的研究最近才逐渐起步。此种关联 可以大大加深对各种非线性输运现象的认识,并对如何从材料控制上调节非线性现象的强度提供有价 值的研究视角和指导原则。基于此背景,本文试图引入研究输运现象的半经典理论框架,并在几种输 运现象中举例说明贝利相的作用。     

贝利相与非线性输运

电子输运现象包含一系列很重要的材料性质,并可以用来提供关于载体物理系统的很多信息。在 最近的二三十年,人们逐渐认识到除了电子能谱之外,电子在布里渊区的几何性质,比如贝利曲率和 轨道磁矩,会在电子输运中起到关键性的作用。在线性输运现象中的此种关联已引起广泛的兴趣并得 到深入的研究。然而,在非线性输运现象中的电子几何性质的作用的研究最近才逐渐起步。此种关联 可以大大加深对各种非线性输运现象的认识,并对如何从材料控制上调节非线性现象的强度提供有价 值的研究视角和指导原则。基于此背景,本文试图引入研究输运现象的半经典理论框架,并在几种输 运现象中举例说明贝利相的作用。     

A method to stabilize the incident X‐ray energy for anomalous diffraction measurements

A method to calibrate and stabilize the incident X‐ray energy for anomalous diffraction data collection is provided and has been successfully used at the single‐crystal diffraction beamline 1W2B at the Beijing Synchrotron Radiation Facilities. Employing a feedback loop to control the movement of the double‐crystal monochromator, this new method enables the incident X‐ray energy to be kept within a 0.2 eV range at the inflection point of the absorption edge.     

Operators of observables for a neutral particle with anomalous magnetic moment in an electromagnetic field

The explicit form of operators of kinetic momenta and spin projection for a neutral particle with an anomalous magnetic moment in constant homogeneous electromagnetic field is found. The possible applications of the obtained results in neutrino physics are considered.     

Stochastic Resonance in a Simple Threshold Sensor System with Alpha Stable Noise

We investigate the effect of alpha stable noise on stochastic resonance in a single-threshold sensor system by analytic deduction and stochastic simulation. It is shown that stochastic resonance occurs in the threshold system in alpha stable noise environment, but the resonant effect becomes weakened as the alpha stable index decreases or the skewness parameter of alpha stable distribution increases. In particular, for Cauchy noise a nonlinear relation among the optimal noise deviation parameter, the signal amplitude and the threshold is analytically obtained and illustrated by using the extreme value condition for the output signal-to-noise ratio. The results presented in this communication should have application in signal detection and image restoration in the non-Gaussian noisy environment.     

傅里叶变换实时红外光谱复原的FPGA实现

为实时获取战场激光、大气污染物气体、毒气等待测物光谱信息的光谱复原,设计了基于现场可编程门阵列(FPGA) 的实时光谱采集分析系统。该系统选用迈克尔逊干涉具和碲镉汞探测器获取待测光谱信息,将采集到的数据传入FPGA。利用硬件描述语言VerilogHDL在Xilinx FPGA芯片上依据傅里叶变换(FFT)实现干涉条纹到光谱数据的实时处理。实验结果表明,FPGA实际计算1 024点基2-FFT频谱分布信息与Matlab理论计算结果相同,可满足实时光谱探测的要求。     

Numerical investigation of slow solitons in Bragg gratings with a hyperbolic tangent apodization

This paper numerically and analytically investigates the formation and propagation motion of optical soliton in the Bragg grating.We choose the fibre Bragg grating with hyperbolic tangent apodization in the middle section in order to obtain slower solitons.Optical fibre soliton but not Bragg grating soliton is used as input pulse in the discussion,which is much more approximate to the light source for the practical purpose.We discuss in detail the effects of the soliton’s velocity with some parameters in the process of transmission.The results show that by choosing special parameters,one can make the soliton slow-down with a little distortion and energy decay and obtain tunable time-delay on a small scale.     

Room-temperature anomalous Hall effect and magnetroresistance in (Ga, Co)-codoped ZnO diluted magnetic semiconductor films

This paper reports that the(Ga,Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition.Room-temperature ferromagnetism is observed for the as-grown thin films.The x-ray absorption fine structure characterization reveals that Co 2+ and Ga 3+ ions substitute for Zn 2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin.The ferromagnetic(Ga,Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room temperature.The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed.     

Fractional backward Kolmogorov equations

This paper derives the fractional backward Kolmogorov equations in fractal space-time based on the construction of a model for dynamic trajectories. It shows that for the type of fractional backward Kolmogorov equation in the fractal time whose coefficient functions are independent of time, its solution is equal to the transfer probability density function of the subordinated process X(Sα(t)), the subordinator Sα(t) is termed as the inverse-time α-stable subordinator and the process X(τ) satisfies the corresponding time homogeneous Ito stochastic differential equation.     

Quantum anomalous Hall effect and giant Rashba spin-orbit splitting in graphene system co-doped with boron and 5d transition-metal atoms

Quantum anomalous Hall effect (QAHE) is a fundamental quantum transport phenomenon in condensed matter physics. Until now, the QAHE has only been experimentally realized for Cr/V-doped (Bi, Sb)₂Te₃ but at an extremely low observational temperature, thereby limiting its potential application in dissipationless quantum electronics. By employing first-principles calculations, we study the electronic structures of graphene co-doped with 5d transition metal and boron atoms based on a compensated n–p co-doping scheme. Our findings are as follows: i) The electrostatic attraction between the n- and p-type dopants effectively enhances the adsorption of metal adatoms and suppresses their undesirable clustering. ii) Hf-B and Os-B co-doped graphene systems can establish long-range ferromagnetic order and open larger nontrivial band gaps because of the stronger spin-orbit coupling with the non-vanishing Berry curvatures to host the high-temperature QAHE. iii) The calculated Rashba splitting energies in Re–B and Pt–B co-doped graphene systems can reach up to 158 and 85 meV, respectively, which are several orders of magnitude higher than the reported intrinsic spin-orbit coupling strength.