硅烯：一种新型的二维狄拉克电子材料

硅烯是单原子层的硅薄膜,其结构与石墨烯类似,由于其奇特的物理性质特别是狄拉克—费米特性,在近年来引起了人们的关注。文章简要介绍了硅烯这一全新的二维体系在实验上的一些进展,包括实现硅烯在表面上的外延生长,重构的结构表征和相变,狄拉克电子特性的证实,以及可能具有的超导转变等。     

硅烯:一种新型的二维狄拉克电子材料

要硅烯是单原子层的硅薄膜,其结构与石墨烯类似,由于其奇特的物理性质特别是狄拉克—费米特性,在近年来引起了人们的关注。文章简要介绍了硅烯这一全新的二维体系在实验上的一些进展,包括实现硅烯在表面上的外延生长,重构的结构表征和相变,狄拉克电子特性的证实,以及可能具有的超导转变等。     

神奇材料graphene在室温下出现量子霍尔效应

graphene是一种由单层碳原子构成的材料，由于具有很多奇异特性，而且其中的电子在很多方面如同无质量的狄拉克费米子，因此近来备受关注。最近又传出关于它的惊人发现，graphene在室温下出现量子霍尔效应。     

石墨烯量子霍尔平台与平台之间转变的标度律关系

在2到50 K温度范围内测量了单层石墨烯量子霍尔平台与平台之间转变的标度律关系. 发现石墨烯的标度律指数κ不是普适的,在低温段的κ大约是0.13,在高温段的κ大约是0.33. 这一结果进一步验证了石墨烯中长程散射的主导地位. 关键词： 石墨烯 量子霍尔效应 标度律     

石墨烯中的Berry几何相

用量子绝热定理推导石墨烯中的Berry几何相,结果发现,由于石墨烯特有的基态能级特性,使其出现了π的几何相,这是引起反常量子霍尔效应最根本的原因。     

双层转角石墨烯的结构和电学性质

石墨烯是第一个被发现的层状二维材料,它的电学性质对层数和层间的堆垛方式有很强的 依赖性。而层间的转角可以被看作是调控石墨烯电学性质的又一个可控的自由度。本文主要综述 双层转角石墨烯的基本结构与性质,重点讲述转角对双层石墨烯电学性质的影响。我们将从理论 与实验结合的角度出发,介绍双层转角石墨烯中Dirac 费米子的新奇物理特性,重点阐述如何通 过转角来调控石墨烯的电学性质。最后我们对双层转角石墨烯的研究现状进行总结和展望。     

含外规范场和动力学费米子自能的狄拉克算符及费米子凝聚

将非阿贝尔规范理论中狄拉克算符行列式的计算从传统的只能含有硬费米子质量项的情况推广到可以含有动量相关的费米子自能的情况，并且行列式与费米子凝聚的计算都被推广到使之能够含有任意的外规范场. 关键词： 费米子自能 外规范场 狄拉克算符的行列式 费米子凝聚     

Br掺杂对石墨烯带隙影响的实验研究

石墨烯独特的结构和性能使其在纳米电子、半导体器件等领域成为研究的热点,但其零带隙的特性严重限制了其应用.采用化学气化沉积法制备了多层石墨烯,并使用溴蒸汽对制备的多层石墨烯进行掺杂,分析研究了溴蒸汽化学掺杂对石墨烯带隙的影响.为了对比溴蒸汽掺杂对石墨烯带隙的影响,使用633 nm He-Ne光分别测量了石墨烯掺杂前和掺杂后的拉曼光谱,根据拉曼光谱计算了石墨烯费米能级移动与掺杂溴蒸汽之间的关系.实验结果表明:溴蒸汽掺杂对石墨烯拉曼光谱G带产生影响;随着掺杂溴蒸汽体积的增加,拉曼光谱G带向高频移动并逐渐趋于稳定;G带和2D带强度比也迅速增加,并最终趋于稳定.费米能级的移动与G峰位置成线性关系,利用G峰峰值位置与费米能级实验关系式计算了溴掺杂后石墨烯的费米能级,分析了化学掺杂对石墨烯带隙的影响.     

拓扑绝缘体简介

拓扑绝缘体是最近几年发现的一种全新的物质形态,由于其独特的能带结构,具有零质量的狄拉克费米子及其相关的奇妙物理特性,近些年来引起了人们的广泛关注.同时,它还展现出在自旋电子学和量子计算等领域巨大的应用前景.     

Detection of hidden localized states by the quantum Hall effect in graphene

We fabricated a monolayer graphene transistor device in the shape of the Hall-bar structure, which produced an exactly symmetric signal following the sample geometry. During electrical characterization, the device showed the standard integer quantum Hall effect of monolayer graphene except for a broader range of several quantum Hall plateaus corresponding to small filling factors in the electron region. We investigated this anomaly on the basis of localized states owing to the presence of possible electron traps, whose energy levels were estimated to be near the Dirac point. In particular, the inequality between the filling of electrons and holes was ascribed to the requirement of excess electrons to fill the trap levels. The relations between the quantum Hall plateau, Landau level, and filling factor were carefully analyzed to reveal the details of the localized states in this graphene device.     

The enigma of the quantum Hall effect in graphene

We apply Laughlin’s gauge argument to analyze the ν=0 quantum Hall effect observed in graphene when the Fermi energy lies near the Dirac point, and conclude that this necessarily leads to divergent bulk longitudinal resistivity in the zero temperature thermodynamic limit. We further predict that in a Corbino geometry measurement, where edge transport and other mesoscopic effects are unimportant, one should find the longitudinal conductivity vanishing in all graphene samples which have an underlying ν=0 quantized Hall effect. We argue that this ν=0 graphene quantum Hall state is qualitatively similar to the high field insulating phase (also known as the Hall insulator) in the lowest Landau level of ordinary semiconductor two-dimensional electron systems. We establish the necessity of having a high magnetic field and high mobility samples for the observation of the divergent resistivity as arising from the existence of disorder-induced density inhomogeneity at the graphene Dirac point.     

Theory of the integer quantum Hall effect in graphene

A Hall resistivity formula for the 2DES in graphene is derived from the zero-mass Dirac field model adopting the electron reservoir hypothesis. The formula reproduces perfectly the experimental resistivity data [K.S. Novoselov, et al., Nature 438 (2005) 201]. This perfect agreement cannot be achieved by any other existing models. The electron reservoir is shown to be the 2DES itself.     

Two-terminal quantized conductance in inhomogeneous graphene

Quantized two-terminal conductance plateaus in graphene were observed and were explained through the mechanism of different Landau level filling factors in inhomogeneous sample. Furthermore, the quantized conductance plateaus are different due to the difference of the carrier exchange through the graphene-substrate interface during the increasing and decreasing gate voltage-sweeps.     

Quantum antidot as an electrometer:Observation of fractional charge

In experiments on resonant tunneling through a quantum antidot in the quantum Hall (QH) regime, we observe periodic conductance peaks both versus magnetic field and a global gate voltage, i.e., electric field. Each conductance peak can be attributed to tunneling through a quantized antidot-bound state. The fact that the variation of the uniform electric field produces conductance peaks implies that the deficiency of the electrical charge on the antidot is quantized in units of charge of quasiparticles of surrounding QH condensate. The period in magnetic field gives the effective area of the antidot state through which tunneling occurs, the period in electric field (obtained from the global gate voltage) then constitutes a direct measurement of the charge of the tunneling particles. We obtain electron charge C in the integer QH regime, and quasiparticle charge C for the QH state.     

Anyons and the quantum Hall effect—A pedagogical review

The dichotomy between fermions and bosons is at the root of many physical phenomena, from metallic conduction of electricity to super-fluidity, and from the periodic table to coherent propagation of light. The dichotomy originates from the symmetry of the quantum mechanical wave function to the interchange of two identical particles. In systems that are confined to two spatial dimensions particles that are neither fermions nor bosons, coined “anyons”, may exist. The fractional quantum Hall effect offers an experimental system where this possibility is realized. In this paper we present the concept of anyons, we explain why the observation of the fractional quantum Hall effect almost forces the notion of anyons upon us, and we review several possible ways for a direct observation of the physics of anyons. Furthermore, we devote a large part of the paper to non-abelian anyons, motivating their existence from the point of view of trial wave functions, giving a simple exposition of their relation to conformal field theories, and reviewing several proposals for their direct observation.     

The 2D Kramers–Dirac oscillator

The Dirac oscillator was initially introduced as a Dirac operator which is linear in momentum and coordinate variables. In contrast to the usual 2D Dirac oscillator, the 2D Kramers–Dirac oscillator admits the time-reversal symmetry, which is a reason for the present nomenclature. It is shown that there exists a family of eigenstates associated with an eigenvalue linear in the control parameter, and the eigenvalue in question goes down from positive values to negative values as the parameter varies in the positive direction. The other eigenvalues are broken up into two bands, positive and negative. The 2D Dirac and the 2D Kramers–Dirac oscillators are compared in their physical grounds and in their spectral structure from the viewpoint of the time-reversal symmetry.     

量子信息讲座 第六讲 量子隐形传态

量子隐形传态是一个新颖和有趣的研究课题。它是量子力学奇妙特性的一种应用。文章阐述了量子隐形传态的基本原理,以及ＥＰＲ效应,Ｂｅｌｌ基测量等相关的概念,并介绍了基于量子光学技术而实现的两个量子隐形传态的成功实验。     

Anomalous quantum Hall effect induced by nearby quantum dots

Transport measurements in high magnetic fields have been performed on two-dimensional electron system (2DES) separated by a thin barrier layer from a layer of InAs self-assembled quantum dots (QDs). Clear feature of quantum Hall effect was observed in spite of presence of QDs nearby 2DES. However, both magnetoresistance, ρ_xx, and Hall resistance, ρ_xy, are suppressed significantly only in the magnetic field range of filling factor in 2DES ν<1 and voltage applied on a front gate . The results indicate that the electron state in QDs induces spin-flip process in 2DES.