Optical tuning of Berry phase effect in topological insulators

We theoretically discuss the influence of driving laser field on the topological nature, one of the manifestation of the electron Berry phase effect, in two-dimensional electronic systems. Adiabatic change of the laser amplitude with circular polarization alters the “order parameter”, termed the Chern number, in topological insulator with broken time-reversal symmetry, resulting in photo-induced phase transition. The finding is an optical analog of the integer quantum Hall effect, that is triggered by the laser field instead of magnetic field. This parallelism suggests the similarity of effects to electron dynamics between circularly polarized light and magnetic field.     

Optical reflection properties for the interface associated with Chern insulator and chiral metamaterial

Based on the topological nature of Chern insulator and magnetoelectric coupling of chiral metamaterial, we investigate the electrodynamics for the interface associated with the two media. The Fresnel coefficients of the interface between Chern insulator and chiral metamaterial, as well as the corresponding polarization rotation angles, are derived. The reflection characteristics of the linearly polarized incident wave at the interface, such as complete polarization conversion and change of polarization state, are discussed. Under the combined influence of Chern insulator and chiral metamaterial, the partial polarization conversion may be enhanced to the complete polarization conversion, and the chiral metamaterial may compensate for the suppression effect of longitudinal conductivity of Chern insulator on the polarization conversion.     

Pseudo topological insulators

We predict pseudo topological insulators that have been previously overlooked. We determine some conditions under which robust pseudo topological edge states appear and illustrate our idea on the Su–Schrieffer–Heeger (SSH) model with extra chiral symmetry breaking potentials. We discuss that pseudo topological insulating phase transition occurs without band gap closing.     

纳米尺度下超导体和拓扑绝缘体的电输运特性

超导体和拓扑绝缘体研究是当前凝聚态物理领域中的重大课题.文章重点介绍了作者所在实验室在纳米超导和拓扑绝缘体电输运领域的实验进展,其中包括金属和铁磁纳米线中的超导近邻效应、半金属纳米线中的新奇超导特性、拓扑绝缘体薄膜中的量子输运以及超导态-拓扑量子态的相互作用等,并对该领域的进一步发展进行了展望.     

Electron transport properties of three-dimensional topological insulators

We review experimental advances in the study of the electron transport in three-dimensional topological insulators with emphasis on experiments that attempted to identify the surface transport. Recent results on transport properties of topological insulator thin films will be discussed in the context of weak antilocalization and electron-electron interactions. Current status of gate-voltage control of the chemical potential in topological insulators will also be described.     

Transport properties of topological insulators films and nanowires

The last several years have witnessed the rapid developments in the study and understanding of topological insulators. In this review, after a brief summary of the history of topological insulators, we focus on the recent progress made in transport experiments on topological insulator films and nanowires. Some quantum phenomena, including the weak antilocalization, the Aharonov-Bobm effect, and the Shubnikov-de Haas oscillations, observed in these nanostructures are described. In addition, the electronic transport evidence of the superconducting proximity effect as well as an anomalous resistance enhancement in topological insulator/superconductor hybrid structures is included.     

Z2拓扑不变量与拓扑绝缘体

文章回顾了几种Z2拓扑数的计算方法,并详细介绍了一种用非阿贝尔贝里联络表示绝缘体Z2不变量的计算方法.这种方法可以确定出一般能带绝缘体的拓扑性质,而不需要限定波函数的规范.利用这种新方法,文章作者计算了二维石墨烯(graphene)系统的Z2拓扑数,得到了和以前研究相一致的结论.     

Z_2拓扑不变量与拓扑绝缘体

文章回顾了几种Z2拓扑数的计算方法,并详细介绍了一种用非阿贝尔贝里联络表示绝缘体Z2不变量的计算方法.这种方法可以确定出一般能带绝缘体的拓扑性质,而不需要限定波函数的规范.利用这种新方法,文章作者计算了二维石墨烯(graphene)系统的Z2拓扑数,得到了和以前研究相一致的结论.     

Thermoelectric effects and topological insulators

The recent discovery of topological insulators(TIs) offers new opportunities for the development of thermoelectrics,because many TIs(like Bi_2Te_3) 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 twodimensional 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.     

Photonic band gap and defect mode from a layered periodic structure with anisotropic nonmagnetic right-handed and left-handed metamaterials

We demonstrate a photonic band gap (PBG) from a layered periodic structure containing anisotropic nonmagnetic right-handed and left-handed metamaterials whose permittivity elements are partially negative. A set of criteria imposed on materials and structures to realize a PBG is derived, and the transmission spectra are also discussed. When a defect layer is introduced, some unusual properties are found in contrast to that of a defect mode in ordinary PBG structures.     

二维拓扑绝缘体退相干效应研究

拓扑绝缘体是当前凝聚态物理研究的热点.退相干效应对该体系的影响的研究不仅有重要的理论意义,而且也是实现未来量子器件的不可或缺的前期工作.文章作者从理论上研究了退相干对二维拓扑绝缘体特别是量子自旋霍尔效应的影响.研究结果表明,作为量子自旋霍尔效应的标志的量子化纵向电阻平台对不破坏自旋记忆的退相干效应（普通退相干）不敏感,但却对破坏自旋记忆的退相干效应（自旋退相干）非常敏感.因此,该量子化平台只能在尺寸小于自旋退相干长度的介观样品中存在,从而解释了量子自旋霍尔效应实验中所观测到的结果(见Science ,20     

磁性拓扑绝缘体中的量子化反常霍尔效应

文章从平常霍尔效应出发,介绍了反常霍尔效应及其内秉物理机制,并在此基础上介绍了其量子化版本——量子化反常霍尔效应.然后从拓扑有序态的角度,重点讨论了量子化反常霍尔效应与量子霍尔效应、量子自旋霍尔效应、拓扑绝缘体等之间的区别与内在联系.最后介绍了通过在拓扑绝缘体（Bi2Se3, Bi2Te3 和 Sb2Te3）薄膜中掺杂过渡金属元素（Cr 或 Fe）实现量子化反常霍尔效应的方法.     

二维拓扑绝缘体退相干效应研究

拓扑绝缘体是当前凝聚态物理研究的热点.退相干效应对该体系的影响的研究不仅有重要的理论意义,而且也是实现未来量子器件的不可或缺的前期工作.文章作者从理论上研究了退相干对二维拓扑绝缘体特别是量子自旋霍尔效应的影响.研究结果表明,作为量子自旋霍尔效应的标志的量子化纵向电阻平台对不破坏自旋记忆的退相干效应(普通退相干)不敏感,但却对破坏自旋记忆的退相干效应(自旋退相干)非常敏感.因此,该量子化平台只能在尺寸小于自旋退相干长度的介观样品中存在,从而解释了量子自旋霍尔效应实验中所观测到的结果(见Science,2007,318:766).同时,文章作者还定义了一个新的物理量,即自旋霍尔电阻,并发现该自旋霍尔电阻也有量子化平台.特别是该量子化平台对两种类型的退相干都不敏感.这说明在宏观样品中也能观测到自旋霍尔电阻的量子化平台,因此更能全面地反映量子自旋霍尔效应的拓扑特性.     

三维拓扑绝缘体antidot阵列结构中的磁致输运研究

利用聚焦离子束刻蚀技术在拓扑绝缘体Bi_2Se_3薄膜中刻蚀了纳米尺度的反点(antidot)阵列,并对制作的三个器件进行了系统的电学输运测量研究.低温下,所有器件中都观察到明显的弱反局域化效应.通过对弱反局域化效应的分析,发现器件一(Dev-1,不含有antidot阵列)和器件二(Dev-2,含有周期较大的antidot阵列)是始终由一个导电通道主导的量子输运系统,但在器件三(Dev-3,含有周期较小的antidot阵列)中能明确观察到较低温度下存在两个独立的导电通道,而在较高温度下Dev-3表现为由一个导电通道主导的量子输运系统.     

Negative refractive index in chiral spiral metamaterials at terahertz frequencies

A three-dimensional chiral metamaterial consisting of arrays of the multi-layered mutually twisted metallic spirals is proposed. We theoretically demonstrate such a chiral spiral structure exhibiting negative refractive index at terahertz frequencies. The chirality with varied refractive index can be obtained by change of configurations of the structure. The presented design offers flexibility for investigation of electromagnetic properties of chiral metamaterials in the terahertz regime and thus leads to a unique route to terahertz device applications.     

拓扑绝缘体电子态的电场调控

文章简要介绍了对拓扑绝缘体性质的电场控制,主要包括三维拓扑绝缘体表面磁性的电场控制、电子在p-n结中的类光输运行为以及拓扑绝缘体量子点的特性.     

Spin-plasmons in topological insulator

Collective plasmon excitations in a helical electron liquid on the surface of strong three-dimensional topological insulator are considered. The properties and internal structure of these excitations are studied. Due to spin-momentum locking in helical liquid on a surface of topological insulator, the collective excitations should manifest themselves as coupled charge- and spin-density waves.     

Efficiency of electrical manipulation in two-dimensional topological insulators

We investigate the efficiency of electrical manipulation in a two-dimensional topological insulator by inspecting the electronic states of a lateral electrical potential superlattice in the system. The spatial distribution of the electron density in the system can be tuned by changing the strength of the externally applied lateral electrical superlattice potential. This provides us the information about how efficiently one can manipulate the electron motion inside a two-dimensional topo- logical insulator. Such information is important in designing electronic devices, e.g., an electric field effect transistor made of the topological insulator. The electronic states under various conditions are examined carefully. It is found that the dispersion of the mini-band and the electron distribution in the potential well region both display an oscillatory behavior as the potential strength of the lateral superlattice increases. The probability of finding an electron in the potential well region can be larger or smaller than the average as the potential strength varies. These features can be attributed to the coupled multiple-band nature of the topological insulator. In addition, it is also found that these behaviors are not sensitive to the gap parameter of the two-dimensional topological insulator model. Our study suggests that the electron density manipulation via electrical gating in a two-dimensional topological insulator is less effective and more delicate than that in a traditional single-band semiconductor.     

Electrostatic field effects on three-dimensional topological insulators

Three-dimensional topological insulators are a new class of quantum matter which has interesting connections to nearly all main branches of condensed matter physics. In this article, we briefly review the advances in the field effect control of chemical potential in three-dimensional topological insulators. It is essential to the observation of many exotic quantum phenomena predicted to emerge from the topological insulators and their hybrid structures with other materials. We also describe various methods for probing the surface state transport. Some challenges in experimental study of electron transport in topological insulators will also be briefly discussed.