逆向诊断劣质绝缘子的快速优化算法分析

针对劣质绝缘子电场逆问题计算量大的缺点,在传统模拟电荷法建模的基础之上采用快速多极子算法对其进行预处理,给出了基本计算原理,并采用Tikhonov正则化方法处理因测量数据干扰引起的逆问题解的不适定性,以及采用牛顿迭代法搜索逆问题的最优解,得到绝缘子模型的场源参数,从而实现对劣质绝缘子的检测。通过构造基本点电荷系模型对该快速优化算法进行可行性验证,最后将该算法应用于110 kV猫头型三相绝缘子串的一相绝缘子进行了实例计算,结果表明：该快速优化算法能够快速有效地实现对劣质绝缘子的在线诊断。     

三聚化非厄密晶格中具有趋肤效应的拓扑边缘态

近年来,探索新的拓扑量子结构、深入分析各种多聚化拓扑晶格中的新奇物理性质已经成为热点.并且,多聚化拓扑模型在量子光学等领域的研究也愈发深入,拥有广阔的发展前景.本文聚焦于研究三聚化非厄密晶格中的新奇拓扑特性.首先,若晶胞内最近邻正反向耦合不相等,三聚化模型中的体态和边缘态出现趋肤效应.其中,随着最近邻耦合正反系数差的增大,拓扑保护的边缘态的宽度和简并度均可被调制,边缘态数量也会减少.其次,当在考虑次近邻耦合的影响时,随着次近邻耦合系数在适当范围内变化,系统本征能谱的上下能隙及其中具有趋肤效应的边缘态也会发生不对称的变化.此外,当适当改变两种耦合系数,三聚化非厄密模型的体态和边缘态的局域程度也会随之发生变化.     

Interband excitations in the 1D limit of two-band fractional Chern insulators

We investigate the stability of the one-dimensional limit of $\nu =1/3$ Laughlin-like fractional Chern insulator with respect to the interband interaction. We propose a construction for the excitations in the infinite-interaction case and show that the energy gap remains finite in the thermodynamic limit. Next, by means of exact diagonalization and Density Matrix Renormalization Group approaches, we consider deviations from ideal dimerization and show that they reduce the stability of the FCI-like states. Finally, to show that our approach is not restricted to one model, we identify the dimer structure behind the thin-torus limit of other system – the checkerboard lattice.     

Dephasing effects in topological insulators

Topological insulators, a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface. The spin-momentum locked surface states and peculiar transport properties exhibit promising potential applications on quantum devices, which generate extensive interest in the last decade. Dephasing is the process of the loss of phase coherence, which inevitably exists in a realistic sample. In this review, we focus on recent progress in dephasing effects on the topological insulators. In general, there are two types of dephasing processes: normal dephasing and spin dephasing. In two-dimensional topological insulators, the phenomenologically numerical investigation shows that the longitudinal resistance plateaus is robust against normal dephasing but fragile with spin dephasing. Several microscopic mechanisms of spin dephasing are then discussed. In three-dimensional topological insulators, the helical surface states exhibit a helical spin texture due to the spin-momentum locking mechanism. Thus, normal dephasing has close connection to spin dephasing in this case, and gives rise to anomalous “gap-like” feature. Dephasing effects on properties of helical surface states are investigated.     

Quantum oscillations and nontrivial transport in(Bi_(0.92)In_(0.08))_2Se_3

Quantum phase transition in topological insulators has drawn heightened attention in condensed matter physics and future device applications.Here we report the magnetotransport properties of single crystalline(Bi_(0.92)In_(0.08))_2Se_3.The average mobility of～1000 cm~2·V~(-1)·s~(-1)is obtained from the Lorentz law at the low field(3 T)up to 50 K.The quantum oscillations rise at a field of～5 T,revealing a high mobility of～1.4×10~4cm~2·V~(-1)·s~(-1)at 2 K.The Dirac surface state is evident by the nontrivial Berry phase in the Landau–Fan diagram.The properties make the(Bi_(0.92)In_(0.08))_2Se_3a promising platform for the investigation of quantum phase transition in topological insulators.     

Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures

Conversion of thermal energy into magnonic spin currents and/or effective electric polarization promises new device functionalities. A versatile approach is presented here for generating and controlling open circuit magnonic spin currents and an effective multiferroicity at a uniform temperature with the aid of spatially inhomogeneous, external, static electric fields. This field applied to a ferromagnetic insulator with a Dzyaloshinskii–Moriya type coupling changes locally the magnon dispersion and modifies the density of thermally excited magnons in a region of the scale of the field inhomogeneity. The resulting gradient in the magnon density can be viewed as a gradient in the effective magnon temperature. This effective thermal gradient together with local magnon dispersion result in an open-circuit, electric field controlled magnonic spin current. In fact, for a moderate variation in the external electric field the predicted magnonic spin current is on the scale of the spin (Seebeck) current generated by a comparable external temperature gradient. Analytical methods supported by full-fledge numerics confirm that both, a finite temperature and an inhomogeneous electric field are necessary for this emergent non-equilibrium phenomena. The proposal can be integrated in magnonic and multiferroic circuits, for instance to convert heat into electrically controlled pure spin current using for example nanopatterning, without the need to generate large thermal gradients on the nanoscale.     

Harmonic generation in keldysh-type models

Summary We shall investigate two models of harmonic generation in the spirit of the Keldysh theory and we shall apply these models to hydrogen, for which more exact data for the rates of this process are available. Although our models correctly describe the angular distribution, the intensity dependence (in the perturbation regime) and the selection rule for odd harmonics, they badly fail in their predictions of the correct order of magnitude of the rates, in particular, of the formation of a plateau. These latter findings disagree with the results of a similar model calculation by Beckeret al. for a δ-function potential. The author of this paper has agreed to not receive the proofs for correction. This research was supported in part by the Natural Sciences and Engineering Research Council of Canada.     

Physical properties of hydrogenated amorphous gallium arsenide

Summary The elemental composition and the optical properties of hydrogenated amorphous GaAs prepared by r.f. reactive sputtering at different hydrogen and argon pressure and substrate temperature have been determined. From the dependence of the absorption coefficient on photon energy the optical gap has been deduced according to the Tauc law. The data obtained for stoichiometric samples are compared with similar data obtained by different authors. The influence of various deposition parameters on stoichiometry and on the optical properties is briefly discussed.     

Electrical and optical properties of CuIn5S8 single crystals

Summary Several transport and optical properties have been studied onn-type CuIn₅S₈ single crystals. The energy gap at 0 K was determined from the electrical measurements to be 1.4 eV. An anisotropy of the magnetoresistance effect was found and it was suggested that the minima of the conduction band were located at points along the [100] directions ink-space. An optical-absorption band was found in an infrared region of (1÷1.6) μm and was attributed to the transitions from the lowest conduction band situated along the [100] directions to an upper conduction band. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Magnetoconductance oscillations and hall current for a two-dimensional electron gas with harmonic confining potential

Summary In the present paper we calculate exactly the density of states of an ideal 2DEG in uniform magnetic and electric fields with parabolic confining potential. From the density of states, we obtain the magnetoconductance oscillations. Consequently, we get the Hall current by means of the Feynman-Hellman theorem and study its quantization.

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Riassunto In questo lavoro si calcola esattamente la densità degli stati di un ideale 2DEG in campi uniformi magnetici ed elettrici con potenziale confinante parabolico. Dalla densità degli stati si ottengono le oscillazioni di magnetoconduttanza. Di consequenza si ricava la corrente di Hall per mezzo del teorema di Feynman-Hellman e si studia la sua quantizzazione.

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Резюме В этой работе мы проводим точное вычисление плотности состояний идеального даумерного электронного газа в однородных магнитных и электрических полях с параболическим удерживаущим потенциалом. Из плотности состояний мы получаем осцилляции магнитной проводимости. Таким образом, мы определяем ток Холла с помощью теоремы фейнмана-Гелмана и исследуем его квантование.