Optical forces from an evanescent wave on a magnetodielectric small particle

We report the first study on the optical force exerted by an evanescent wave on a small sphere with both electric and magnetic responses to the incident field, immersed in an arbitrary nondissipative medium. New expressions and effects from their gradient, radiation pressure, and curl components are obtained owing to the particle induced electric and magnetic dipoles, as well as to their mutual interaction. We predict possible dramatic changes in the force depending on the host medium, the polarization, and the nature of the surface wave.     

Ferroelectricity in spiral magnets

It was recently observed that the ferroelectrics showing the strongest sensitivity to an applied magnetic field are spiral magnets. We present a phenomenological theory of inhomogeneous ferroelectric magnets, which describes their thermodynamics and magnetic field behavior, e.g., dielectric susceptibility anomalies at magnetic transitions and sudden flops of electric polarization in an applied magnetic field. We show that electric polarization can also be induced at domain walls and that magnetic vortices carry electric charge.     

Effect of mechanical force on domain switching in BiFeO_3 ultrathin films

Ferroelectric polarization can be switched by an external applied electric field and may also be reversed by a mechanical force via flexoelectricity from the strain gradient.In this study,we report the mechanical writing of an epitaxial BiFeO3(BFO)thin film and the combined action of an applied mechanical force and electric field on domain switching,where the mechanical force and electric field are applied using the tip of atomic force microscopy.When the applied force exceeds the threshold value,the upward polarization of the BFO thin film can be reversed by pure mechanical force via flexoelectricity;when an electric field is simultaneously applied,the mechanical force can reduce the coercive electric field because both the piezoelectricity from the homogeneous strain and the flexoelectricity from strain gradient contribute to the internal electric field in the film.The mechanically switched domains exhibit a slightly lower surface potential when compared with that exhibited by the electrically switched domains due to no charge injection in the mechanical method.Furthermore,both the mechanically and electrically switched domains exhibit a tunneling electroresistance in the BFO ferroelectric tunnel junction.     

Electrostatic interactions of charges and dipoles near a polarizable membrane

A variational method is used to determine the polarization charge density induced on the surfaces of a dielectric slab (a coarse-grained model of a membrane) by electric point charges and extended dipoles. The results are used to obtain analytic expressions for the polarization energy and the resulting forces acting on and between pairs of charges positioned in various geometries relative to the membrane. The polarization effects are shown to be substantial and often non-trivial on the nanometre scale, compared to direct Coulomb interactions.     

Electrical conductivity characteristics of soda-lime-silicate glasses in strong electrical fields after gamma irradiation

Stable radiation-induced changes of electrical conductivity in strong electric fields in soda-lime-silicate glasses is explained using the concept that the accumulation of volume charge creates a high-voltage polarization in the presence of electrons excited by gamma irradiation. It is assumed that the processes of recombination of electrons and sodium cations, and their dissociations, are controlled by the strong electric field.     

Electrical control of magnetism in oxides

Recent progress in the electrical control of magnetism in oxides,with profound physics and enormous potential applications,is reviewed and illustrated.In the first part,we provide a comprehensive summary of the electrical control of magnetism in the classic multiferroic heterostructures and clarify the various mechanisms lying behind them.The second part focuses on the novel technique of electric double layer gating for driving a significant electronic phase transition in magnetic oxides by a small voltage.In the third part,electric field applied on ordinary dielectric oxide is used to control the magnetic phenomenon originating from charge transfer and orbital reconstruction at the interface between dissimilar correlated oxides.At the end,we analyze the challenges in electrical control of magnetism in oxides,both the mechanisms and practical applications,which will inspire more in-depth research and advance the development in this field.     

An Exotic Phase Change in Dynamic Electrorheological Fluids

It is well known that constant or time-varying electric fields can induce phase changes in electrorheological(ER) fluids, from a liquid to semi-solid state, provided the field strength is larger than some critical value. We describe here an experimental and theoretical study considering yet a different class of phase changes, specifically those for an ER fluid in the presence of both shear flow and a time-varying electric field. We note that as the frequency of the field is decreased, the ER fluid will go from a liquid to an intermediate transition state, and eventually to a shear banding state. Our theoretical analysis further indicates that this phase change originates from competing effects of viscous and electrical forces. Ultimately, we conclude that it is possible to achieve various states and corresponding(desired)macroscopic properties of dynamic colloidal suspensions by adjusting the frequency of the externally applied electric field.     

Ferroelectric polarization flop in a frustrated magnet MnWO4 induced by a magnetic field

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO4 with a long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of the ferroelectric phase. An electric polarization flop from the b direction to the a direction has been observed when a magnetic field above 10 T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth 4f moments.     

Volume-Charged Cones on a Liquid Interface in an Electric Field

In this study, we explore a novel type of slender conical liquid meniscus arisen in high electric field, which carries surface charge and net bulk charge of opposite sign. Stability of such dissipative structure is ensured by the balance between capillary and electrostatic forces and competition between the surface and bulk electric currents. The bulk charge is governed by the applied voltage being generated by the electric field of the cone due to dissociation/associations reactions at its apex. The effect of the physical parameters of the liquid on the microcone structure is elucidated. It is shown that the cone angle cannot exceed a critical value, which is a function of dielectric permittivity of the liquid. The electric current through the cone is found to be proportional to the square of the applied voltage. The obtained results can be applied for analysis of atomization processes of various liquids.     

压缩应变载荷下氮化镓隧道结微观压电特性及其巨压电电阻效应

电子器件可控性研究在日益追求器件智能化和可控化的当今社会至关重要. 基于第一性原理和量子输运计算, 本文研究了压缩应变载荷对氮化镓(GaN)隧道结基态电学性质和电流输运的影响, 在原子尺度上窥视了氮化镓隧道结的微观压电性, 验证了其内在的巨压电电阻(GPR)效应. 计算结果表明, 压缩应变载荷可以调节隧道结内氮化镓势垒层的电势能降、内建电场、电荷密度和极化强度, 进而实现对隧道结电流输运和隧穿电阻的调控. 在-1.0 V的偏置电压下, -5%的压缩应变载荷将使氮化镓隧道结的隧穿电阻增至4倍. 本研究展现了氮化镓隧道结在可控电子器件中的应用潜力, 也展现了应变工程在调控电子器件性能方面的光明前景.     

强外电场作用下二甲基硅酮的分子结构和激发态

采用密度泛函(DFT)方法B3P86在6 311++G(d,p)基组水平上优化得到了分子轴方向不同电偶极 场(-0.04～0.04a.u.)作用下,二甲基硅酮的基态电子状态、几何结构、电偶极矩和分子总能量.在优化构型下 用同样的基组采用杂化CIS DFT方法(CIS B3P86)研究了同样外电场条件下对二甲基硅酮的激发能和振子强度 的影响.计算结果表明,分子几何构型与电场大小和方向呈现强烈的依赖,正向电场下基态偶极矩随电场强度线 性增加,分子总能量降低,当反向电场大于0.03a.u.时,偶极距方向改变,总能量增加;激发能随电场增加急剧减 小,且对电场方向的依赖呈现出不对称性,满足Grozema关系.电场对振子强度的影响比较复杂,但仍满足跃迁选 择定则.     

低电场下LiNbO3薄膜在非晶衬底上的取向生长

报道了外加低电场和衬底温度对脉冲激光淀积法制备的LiNbO₃薄膜取向的影响.在衬底温度为600℃和外加电场为7V/cm的条件下，在石英玻璃等非晶态衬底上获得了完全(001)取向的LiNbO₃薄膜.在对具有自发极化的LiNbO₃在电场作用下成核生长机制和温度对LiNbO₃自发极化强度的影响进行分析的基础上，给出了低电场诱导铁电薄膜取向生长的物理依据. 关键词：     

二氢化钚分子激发态结构的外场效应

采用密度泛函(DFT)方法B3LYP/Gen，在Pu为SDD基组、H为6-311++G^**基组水平上优化得到了分子轴方向不同电偶极场(-0.005—0.005a.u.)作用下，二氢化钚的基态电子状态、几何结构、电偶极矩和分子总能量.在优化构型下用同样的基组采用含时密度泛函(TDDFT)方法(TD-B3LYP)研究了同样外电场条件下对二氢化钚的激发能和振子强度的影响.计算结果表明，分子几何构型与电场大小和方向呈现较强的依赖，电场强度增加基态偶极矩随电场强度线性增加，H-Pu-H的角度线性减小，分子总能量线性减小；激发能随电场强度增加而减小，且对电场方向的依赖呈现近似对称性，满足Grozema关系.电场对振子强度的影响比较复杂，但仍满足跃迁选择定则. 关键词： 二氢化钚 激发态 电偶极场 TD-DFT     

Two identical conducting spheres with same potential in a uniform electric field

Interaction, polarization, and charges or electric field distribution of conducting spheres in applied electric field are in many fields including electrorheological fluids, electrophoresis, and electrical engineering. A system with two equipotential conducting spheres in an applied uniform electric field is analyzed by image method. A new method is put forward to calculate the image charges distribution when using image method, which ensures the validity of image method to analyze equipotential cases. An apparatus is constructed to measure the force experimentally as well. Results show that the distribution of electric field and electric interaction are different with the case not equipotential.     

Spin polarization induced by an electric field in the presence of weak localization effects

We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.     

Reprint of : Spin polarization induced by an electric field in the presence of weak localization effects

We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.     

PuH2分子激发态的外场效应

采用密度泛函(DFT)方法B3LYP/Gen,在Pu为SDD基组、H为6-311 G**基组水平上优化得到了分子轴方向不同电偶极场(-0.005~0.005 a.u.)作用下,二氢化钚的基态电子状态、几何结构和分子总能量.在优化构型下用同样的基组采用含时密度泛函(TDDFT)方法(TD-B3LYP)研究了同样外电场条件下对二氢化钚的激发能、振子强度、自旋污染和Pu原子正电荷的影响.计算结果表明,分子几何构型与电场大小和方向呈现较强的依赖,H-Pu-H的角度线性减少,分子总能量线性减少;自旋污染随电场增加线性增加;Pu原子正电荷随电场增加而线性减小;激发能随电场强度增加而减小,且对电场方向的依赖呈现近似对称性,满足Grozema关系.电场对振子强度的影响比较复杂,但仍满足跃迁选择定则.     

外电场下交联聚乙烯电介质材料分子结构变化及其电老化微观机理研究

为了从微观角度分析交联聚乙烯(XLPE)材料的电树枝老化,本文采用分子模拟方法计算并优化得到了XLPE分子结构.沿着聚乙烯链施加不同大小电场强度,分析交联聚乙烯分子的几何结构、偶极矩、极化率、电荷分布、前线轨道能量和红外光谱变化规律.计算结果表明,随着外电场的增大,交联聚乙烯分子红外光谱发生较大变化;当外施电场达到0.026a.u.后,红外光谱图中出现虚频,表明分子空间结构不再稳定,易发生断键;另外从前线轨道图的变化可以看出断键现象最先发生在交联聚乙烯链端部;沿着电场方向,原子所带电荷量由交联处向端部转移,当外施电场达到0.029a.u.后,链端部的C-H和C-C键断裂产生H·和CH_3·自由基.游离的自由基会形成空间电荷并发生积聚,产生局部较大场强,从而进一步影响交联聚乙烯链的空间结构.而电介质内部微观特性的变化必定会导致交联聚乙烯材料绝缘性能的下降,这些变化对揭示交联聚乙烯电缆电树枝形成的微观规律具有重要研究意义.     

外电场作用下苯乙烯分子结构和电子光谱

采用密度泛函B3P86方法在6-311G基组水平上优化得到了在不同外电场(0—0.05a.u.)作用下,苯乙烯分子的基态电子状态、几何结构、电偶极矩和分子总能量.在优化构型下利用杂化CIS-DFT方法(CIS-B3P86)研究了同样外电场条件下对苯乙烯的激发能和振子强度的影响.计算结果表明,分子几何构型与电场大小呈现强烈的依赖关系,分子偶极矩随电场的增加而增大.分子总能量随着电场增加而降低.激发能随电场增加快速减小,表明在电场作用下,分子易于激发和解离. 关键词： 苯乙烯 电场 激发态 杂化CIS-DFT     

Current-induced spin accumulation in lateral superlattices with Rashba and Dresselhaus spin–orbit interaction

The current-induced spin accumulation is calculated for a 1D lateral semiconductor superlattice with spin–orbit interaction of the Rashba and Dresselhaus type. Due to its particular symmetry, the Rashba interaction alone only leads to an in-plane component of the magnetization transverse to the applied electric field. When in addition a Dresselhaus contribution is present, this symmetry is lifted, and all components of the magnetization are induced by the electric field. Based on the density-matrix approach, the induced spin polarization is determined as a function of external in-plane electric and magnetic fields.