Defect-free SrTiO3 (STO) is a band insulator but Angle Resolved Photoemission Spectroscopy (ARPES) experiments have demonstrated the existence of a nanometer thin two-dimensional electron liquid (2DEG) at the (001) oriented surface of this compound. The bulk is a trivial insulator, but our theoretical study reveals that the parity of electronic wavefunctions in this 2DEG is inverted in the vicinity of special points in reciprocal space where the low-energy dispersion consists of four gapped Dirac cones with a tilted and anisotropic shape. This gives rise to linearly dispersing topological edge states at the one-dimensional boundary. We propose to probe these modes by measuring the Josephson radiation from gapless bound Andreev states in STO based junctions, as it is predicted that they display distinctive signatures of topology.
The topological electronic structure plays a central role in the non-trivial physical properties in topological quantum materials. A minimal, hydrogen-atom-like topological electronic structure is desired for researches. In this work, we demonstrate an effort towards the realization of such a system in the intrinsic magnetic topological insulator MnBi2Te4, by manipulating the topological surface state (TSS) via surface modification. Using high resolution laser- and synchrotron-based angle-resolved photoemission spectroscopy (ARPES), we found the TSS in MnBi2Te4 is heavily hybridized with a tri…
Weak topological insulators possess a symmetry related set of Dirac-Weyl cones in the surface Brillouin zone, implying misorientation between the principle axis of the low energy manifold of the bulk and the surface normal. We show that this feature of weak topological insulators comes with a hidden richness of surface spin textures, and that by misorientation a helical texture can become an unusual hyperbolic spin texture. We illustrate this effect by comparison of the $M$-point and $Γ$-point Dirac-Weyl cones on the (111) surface of the crystalline topological insulator SnTe.
Controlling and distinguishing electronic transport of topological and trivial surface states in a topological insulator
拓扑绝缘体（TI）是一类具有狄拉克-费米子拓扑表面态（TSS）特征的新型电子材料，在新物理和器件应用方面具有广阔的应用前景。然而，现实的TI材料的主要挑战是访问，区分和操纵TSS的电子输运经常被其他可能的平行传导通道所掩盖，所述其他可能的平行传导通道包括体以及由于体带的弯曲而在表面附近形成的二维电子气（2DEG）。这样的（薛定谔-费米子）2DEG代表拓扑平凡的表面状态，其共存的TSS已被揭示的角度分辨光电子能谱。在这里，我们表明，表面条件的简单操作可以用来访问和控制这两种类型的表面状态和它们的共存体绝缘Bi 2 Te 2Se，其表面导电突出表现在温度相关的电阻和非局部运输。平凡的二维电子气和TSS在磁电阻中都表现出明显的Shubnikov-de Haas振荡，不同的Berry相位~0和~pi区分了它们不同的拓扑特征。我们还报告了偏离典型的弱反定位行为，可能是由于高流动性TSS。我们的研究能够区分，控制和利用不同拓扑性质的TI表面载流子的电子输运。
Topological Control: Systematic control of topological insulator Dirac fermion density on the surface of Bi2Te3
三维（3D）拓扑绝缘体是具有自旋-轨道诱导的体绝缘带隙的量子材料，其在不存在外加磁场的情况下表现出量子霍尔现象。拓扑绝缘体在器件几何结构中的拟议应用依赖于在狄拉克节点附近调节其表面上的化学势的能力。在这里，我们展示了一套基于光掺杂和分子掺杂相结合的表面控制方法，以系统地调整Bi 2 Te 3的拓扑（111）表面上的狄拉克费米子密度。它们的功效通过使用高分辨率角分辨光电子能谱（ARPES）的直接电子结构拓扑测量来证明。这些结果为探索Bi 2 Te 3表面Dirac电子的拓扑行为提供了新的机会。这里所示的方法中的至少一种可以成功地应用于其他拓扑绝缘体，例如Bi{1-x}Sb{x}、Sb 2 Te 3和Bi 2Se 3，这些将在别处示出。更重要的是，我们的拓扑表面状态操纵的方法在这里展示了非常适合未来的拓扑现象，这将补充从传统的电门控技术获得的传输结果的光谱研究。
We study topological surface-plasmon-polaritons at optical frequencies in diffraction gratings formed by bipartite corrugated metal-dielectric gratings. To do so we implement the theory as developed in Della Valle and Longhi to describe the amplitude of the field by an emergent Schrödinger-like equation. The tri-harmonic grating generates a bipartite Kronig-Penney model. Topologically protected localised modes are then predicted to occur at the edges of the grating and at defects formed by the combination of two mirror antisymmetric corrugations, whose bulk invariant is a step-wise varying Zak…
Gate-tuned Differentiation of Surface-conducting States in Bi1.5Sb0.5Te1.7Se1.3 Topological-insulator Thin Crystals
使用场角，温度和背栅电压依赖性的弱反本地化（WAL）和普遍的电导波动薄Bi 1.5 Sb 0.5 Te 1.7 Se 1.3拓扑绝缘体单晶，结合栅极调谐霍尔电阻率测量，我们可靠地分离的拓扑性质的表面导电体导电和拓扑平凡的表面导电。我们最大限度地减少了晶体中的体传导和背栅调谐费米能级的拓扑底表面带，同时保持顶面不敏感的背栅与最佳晶体厚度？100 nm。我们认为，在相对较低的磁场的载流子的相干扩散运动发生的WAL效应是更重要的比其他运输工具，如Shubnikov-de Hass振荡确认导电的拓扑保护的表面状态。我们的方法提供了一个高度连贯的图片的表面输运性质的TI和一个可靠的手段，调查的基本拓扑性质的表面导电和可能的量子器件的应用相关的动量锁定自旋极化的表面状态。
The quantum size effect has a significant impact on electrons, such that it can even change their topologically protected properties. An example of this phenomenon is the gap opening in the topologically protected gapless surface state in finite-thickness topological-insulator films. However, much is not known about the quantum size effect in topological heterojunctions. In this study, by calculating the single-particle spectrum of Bi/Bi$_{1-x}$Sb$_{x}$ based on the well-known Liu-Allen model, we found that the strong quantum size effect in topological heterojunctions yields an unexpected band…
Nonlinear optical probe of tunable surface electrons on a topological insulator
我们用超快激光脉冲实验证明了拓扑绝缘体Bi $_2$ Se $_3$的体单晶的二阶光学响应对它的表面电子是敏感的。通过进行表面掺杂依赖性测量作为光子偏振和样品取向的函数，我们表明，二次谐波产生可以同时探测表面晶体结构和表面电荷的Bi $_2$ Se $_3$。此外，我们发现，使用圆偏振光的二次谐波产生揭示了系统的时间反演对称性，并且对表面充电具有令人惊讶的鲁棒性，这使其成为拓扑表面和掩埋界面的光谱研究的有前途的工具。
The superconductor PdTe$_2$ is known to host bulk Dirac bands and topological surface states. The coexistence of superconductivity and topological surface states makes PdTe$_2$ a promising platform for exploring topological superconductivity and Majorana bound states. In this work, we report the layer-by-layer molecular beam epitaxy growth and spectroscopic characterization of high quality PdTe$_2$ films with thickness down to 3 monolayers (ML). In the 3 ML PdTe$_2$ film, we observed spin-polarized surface resonance states, which are isolated from the bulk bands due to the quantum size effects…
Topological nature of step edge states on the surface of topological crystalline insulator Pb$_{0.7}$Sn$_{0.3}$Se
除了新颖的表面态，拓扑绝缘体还可以在晶体缺陷处表现出鲁棒的无隙态。台阶边是晶体表面常见的一类缺陷。在这项工作中，我们建立了拓扑晶体绝缘体（TCI）Pb $_{0.7}$ Sn $_{0.3}$ Se的[001]表面的台阶边缘的一维（1D）束缚态的拓扑性质，从理论和实验两方面。我们表明，台阶边缘态的拓扑稳定性来自于表面低能物理的一个紧急粒子-空穴对称性，并展示了粒子-空穴对称性破缺的实验特征。我们还揭示了外部磁场对一维束缚态的影响。我们的工作表明，类似的拓扑阶边模式的可能性，在其他拓扑材料与岩盐结构。
Lifetime and surface-to-bulk scattering off vacancies of the topological surface state in the three-dimensional strong topological insulators Bi2Te3 and Bi2Se3
我们分析的有限寿命的拓扑保护的电子在表面状态的Bi 2 Te 3和Bi 2Se 3由于弹性散射表面空位和能量的函数。散射率被分解成表面到表面和表面到体的贡献，给我们新的基本见解的拓扑表面态（TSS）的散射性质。如果可能的最终体状态的数量远大于最终表面状态的数量，则表面到体的贡献是重要的，否则表面到表面的贡献占主导地位。此外，我们发现缺陷共振，有显着的影响散射特性的TSS。它们可以强烈地改变表面态的寿命，在1at%的表面缺陷浓度下在几十fs到ps之间变化。
Surface potential in a topological matter could unprecedentedly localize the waves. However, this surface potential is yet to be exploited in topological photonic systems. Here, we demonstrate that photonic surface states can be induced and controlled by the surface potential in a dielectric double gyroid (DG) photonic crystal. The basis translation in a unit cell enables tuning of the surface potential, which in turn regulates the degree of wave localization. The gradual modulation of DG photonic crystals enables the generation of a pseudomagnetic field. Overall, this study shows the interpla…
A topological flatband, also known as drumhead states, is an ideal platform to drive new exotic topological quantum phases. Using angle-resolved photoemission spectroscopy experiments, we reveal the emergence of a highly localized possible drumhead surface state in a topological semimetal BaAl4 and provide its full energy and momentum space topology. We find that the observed surface state is highly localized in momentum, inside a square-shaped bulk Dirac nodal loop, and in energy, leading to a flat band and a peak in the density of state. These results establish this class of materials as a p…
Intrinsic topological superconductors have protected gapless Majorana modes, bound and/or propagating, at the natural boundaries of the sample, without requiring field, defect, or heterostructure. We establish the complete classification/construction of intrinsic topological superconductors jointly protected by point-group and time-reversal symmetries in three dimensions. This is obtained from enumerating distinct ways for stacking $n$th-order irreducible building blocks, minimal anomalous surface states of $n$th-order topological superconductors. Particularly, our method provides a unified de…
Identifying open-orbit topological surface states in dual topological semimetal TaSb$_2$
Leibniz Institute for Solid State and Materials Research, IFW Dresden（德累斯顿铁电研究所）；S. N. Bose National Centre for Basic Sciences（S.N. 玻色基础科学国家中心）；Max Planck Institute for Solid State Research（马克斯·普朗克固体研究所）；Helmholtz-Zentrum Berlin für Materialien und Energie, Elektronenspeicherring BESSY II（柏林亥姆霍兹材料与能源中心）
By means of systematically first-principles calculations and model analysis, a complete phase diagram of the body-centered silicon(BC8-Si) via lattice constant a and internal atomic coordinate x is explored, which demonstrates that BC8-Si is a topological Luttinger semimetal(LSM) accompanied with topologically nontrivial surface states, and the electronic properties of BC8-Si can be further tuned to a normal insulator or topological Dirac semimetal by very tiny changing of a and x. These results successfully explain the contradictory transport reports of BC8-Si. More importantly, the topologic…
The surface orientation dependence on the hydrogen evolution reaction (HER) performance of topological crystalline insulator (TCI) SnTe thin films is studied. Their intrinsic activities are determined by linear sweep voltammetry and cyclic voltammetry measurements. It is found that SnTe (001) and (111) surfaces exhibit intrinsic activities significantly larger than the (211) surface. Density functional theory calculations reveal that pure (001) and (111) surfaces are not good electrocatalysts, while those with Sn vacancies or partially oxidized surfaces, with the latter as evidenced by X-ray p…
One of the most remarkable characteristics of topological materials is that they have special surface states, which are determined by the topological properties of their bulk materials. The angle resolved photoemission spectroscopy (ARPES) is a powerful tool to explore the surface states, which allows to further investigate the topological phase transitions. However, it is very difficult to compare the first-principle calculated band structures to the ARPES results,when the systems are doped or alloyed, because the band structures are heavily folded.We develop an efficient band unfolding metho…
Non-Dirac topological surface states in (SnTe)$_{n\geq2}$(Bi$_2$Te$_3$)$_{m=1}$
在层状范德华键合（SnTe）$_{n=2,3}$（Bi $_2$ Te $_3$）$_{m=1}$化合物中发现了一种新型的拓扑自旋螺旋表面态，该化合物在一个结构单元中包含两个共价键合的带反转子系统SnTe和Bi $_2$ Te $_3$.这种新的拓扑状态证明了带隙内的非狄拉克色散。表面态的色散有两个斜率不同的线性段，它们之间有肩状特征。拓扑表面状态的这种分散使得能够通过施加外部电场来有效切换拓扑载流子的速度。
Connection topology of step edge state bands at the surface of a three dimensional topological insulator
Bi $_2$ Se $_3$家族中的拓扑绝缘体表现出跨越拓扑有序体带隙的螺旋狄拉克表面态。最近的扫描隧道显微镜测量已经发现了Bi $_2$ Se $_3$和Bi $_2$ Te $_3$的体带隙中的附加状态，其位于一维台阶边缘。在这里的拓扑绝缘体表面的数值模拟被用来探索边缘状态形成的现象在这些材料上普遍存在的单五层台阶缺陷。一维边缘态与二维表面态Dirac点具有稳定的拓扑连接。
Spin-Polarized Surface Resonances Accompanying Topological Surface State Formation
拓扑绝缘体的自旋极化表面态是由自旋轨道相互作用驱动的体能带的能量反转产生的。在这里，我们发现以前未确定的后果带反转的拓扑绝缘体Bi $_2$ Se $_3$的表面电子结构。通过同时进行自旋，时间，和角度分辨的光电子能谱，我们映射的自旋极化未占电子结构，并确定一个表面共振，这是不同的拓扑表面状态，但共享一个类似的自旋轨道纹理与相反的方向。它的动量依赖性和自旋织构意味着它与拓扑表面态有着密切的联系.计算表明，这两个不同的状态可以出现从平凡的拉什巴类状态，通过自旋轨道诱导带反转改变拓扑结构。因此，这项工作提供了一个令人信服的观点，通过拓扑相变的表面状态的共同演变，使直接测量自旋极化未占用的能带结构的独特能力。
The surface states of 3D topological insulators in general have negligible quantum oscillations when the chemical potential is tuned to the Dirac points. In contrast, we find that topological Kondo insulators can support surface states with an arbitrarily large Fermi surface when the chemical potential is pinned to the Dirac point. We illustrate that these Fermi surfaces give rise to finite-frequency quantum oscillations, which can become comparable to the extremal area of the unhybridized bulk bands. We show that this occurs when the crystal symmetry is lowered from cubic to tetragonal in a m…
Recently, higher-order topological insulators have been attracting extensive interest. Unlike the conventional topological insulators that demand bulk gap closings at transition points, the higher-order band topology can be changed without bulk closure and exhibits as an obstruction of higher-dimensional boundary states. Here, we report the first experimental realization of three-dimensional surface-obstructed topological insulators with using acoustic crystals. Our acoustic measurements demonstrate unambiguously the emergence of one-dimensional topological hinge states in the middle of the bu…
