Emergence of Orbital Angular Momentum by Inversion Symmetry Breaking and Its Detection by ARPES
Choong H. Kim, Jin-Hong Park, Jun Won Rhim, Beom Young Kim, Jaejun Yu, Masashi Arita, Kenya Shimada, Hirofumi Namatame, Masaki Taniguchi, Changyoung Kim, Jung Hoon Han
备注：
5 pages, 2 figures, ARPES experiment on Cu included; author list updated, This version will not be published. A newer version, which is submitted, is available at arXiv:1112.1821
Rashba-split surface band is characterized by a one-to-one correspondence between the electron's momentum k and its spin orientation. Here we show that a similar correspondence between momentum and orbital angular momentum (OAM) must exist on surface bands once the inversion symmetry is broken. The correspondence is valid even when there is no spin-orbit interaction. Tight-binding and first-principles calculations are presented to support our claim. As a method to detect such OAM-momentum correspondence, we propose the circular dichroism (CD) experiment using the angle-resolved photoemission (ARPES) setup. CD-ARPES experiment performed on Cu surface confirms the existence of chiral OAM. A new concept of "orbital Galvanic effect" is proposed.
We investigate the hidden Berry curvature in bulk 2H-WSe2 by utilizing the surface sensitivity of angle resolved photoemission (ARPES). The symmetry in the electronic structure of transition metal dichalcogenides is used to uniquely determine the local orbital angular momentum (OAM) contribution to the circular dichroism (CD) in ARPES. The extracted CD signals for the K and K' valleys are almost identical but their signs, which should be determined by the valley index, are opposite. In addition, the sign is found to be the same for the two spin-split bands, indicating that it is independent of…
FeSe${}_{0.45}$Te${}_{0.55}$ (FeSeTe) has recently emerged as a promising candidate to host topological superconductivity, with a Dirac surface state and signatures of Majorana bound states in vortex cores. However, correlations strongly renormalize the bands compared to electronic structure calculations, and there is no evidence for the expected bulk band inversion. We present here a comprehensive angle resolved photoemission (ARPES) study of FeSeTe as function of photon energies ranging from 15 - 100 eV. We find that although the top of bulk valence band shows essentially no $k_z$ dispersion…
Using angle resolved photoemission spectroscopy (ARPES) and density functional theory (DFT) calculations we studied the low-energy electronic structure of bulk ZrTe$_2$. ARPES studies on ZrTe$_2$ demonstrate free charge carriers at the Fermi level, which is further confirmed by the DFT calculations. An equal number of hole and electron carrier density estimated from the ARPES data, points ZrTe$_2$ to a semimetal. The DFT calculations further suggest a band inversion between Te $p$ and Zr $d$ states at the $Γ$ point, hinting at the non-trivial band topology in ZrTe$_2$. Thus, our studies for th…
We have performed angle-resolved photoemission spectroscopy (ARPES) on CeBi which undergoes a two-step antiferromagnetic (AF) transition with temperature. Soft-x-ray ARPES has revealed the inverted band structure at the X point of bulk Brillouin zone for CeBi (and also for LaBi) as opposed to LaSb with non-inverted band structure. Low-energy ARPES on CeBi has revealed the Dirac-cone band at the Gamma point in the paramagnetic phase associated with the bulk band inversion. On the other hand, a double Dirac-cone band appears on entering the first AF phase at T = 25 K, whereas a single Dirac-cone…
The combination of space inversion and time reversal symmetries result in doubly-degenerate Bloch states with opposite spin. Many lattices with these symmetries can be constructed by combining a noncentrosymmetric potential (lacking this degeneracy) with its inverted copy. Using simple models, we unravel the evolution of local spin-splitting during this process of inversion symmetry restoration, in the presence of spin-orbit interaction and sublattice coupling. Importantly, through an analysis of quantum mechanical commutativity, we examine the difficulty of identifying states that are simulta…
Reexamining Circular Dichroism in Photoemission From a Topological Insulator
Tel Aviv University（特拉维夫大学）；École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院）；University of West Bohemia（西波希米亚大学）；Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory（斯坦福材料能源科学研究所，SLAC国家加速器实验室）；Geballe Laboratory for Advanced Materials, Stanford University（斯坦福大学高威实验室）；Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory（SLAC国家加速器实验室斯坦福同步辐射光源）
Using classical Monte Carlo simulations, we study a simple statistical mechanical model of relevance to the emergence of polarisation from local displacements on the square and cubic lattices. Our model contains two key ingredients: a Kitaev-like orientation-dependent interaction between nearest neighbours, and a steric term that acts between next-nearest neighbours. Taken by themselves, each of these two ingredients is incapable of driving long-range symmetry breaking, despite the presence of a broad feature in the corresponding heat capacity functions. Instead each component results in a "hi…
We study the mechanism of the exceptionally large anomalous Hall effect (AHE) in the noncentrosymmetric antiferromagnet $\mathrm{Co}\mathrm{Nb}_3\mathrm{S}_6$ by angle-resolved photoemission spectroscopy (ARPES) and magnetotransport measurements. From ARPES measurements of $\mathrm{Co}\mathrm{Nb}_3\mathrm{S}_6$ and its family compounds ($\mathrm{Fe}\mathrm{Nb}_3\mathrm{S}_6$ and $\mathrm{Ni}\mathrm{Nb}_3\mathrm{S}_6$), we find a band dispersion unique to the Co intercalation existing near the Fermi level. We further demonstrate that a slight deficiency of sulfur in $\mathrm{Co}\mathrm{Nb}_3\ma…
Dirac semimetals associated with bulk Dirac fermions are well-known in topological electronic systems. In sharp contrast, three-dimensional (3D) Dirac phonons in crystalline solids are still unavailable. Here we perform symmetry arguments and first-principles calculations to systematically investigate 3D Dirac phonons in all space groups with inversion symmetry. The results show that there are two categories of 3D Dirac phonons depending on their protection mechanisms and positions in momentum space. The first category originates from the four-dimensional irreducible representations at the hig…
Topological kagome systems have been a topic of great interest in condensed matter physics due totheir unique electronic properties. The vanadium-based kagome materials are particularly intrigu-ing since they exhibit exotic phenomena such as charge density wave (CDW) and unconventionalsuperconductivity. The origin of these electronic instabilities is not fully understood, and the re-cent discovery of a charge density wave in ScV6Sn6provides a new avenue for investigation. In thiswork, we investigate the electronic structure of the novel kagome metal ScV6Sn6using angle resolvedphotoemission spe…
Epitaxial Growth and Electronic Properties of QuasiFreeStanding Rhombohedral WSe2 Bilayers on Cubic W110
Université Paris-Saclay（巴黎萨克雷大学）；CNRS, Centre de Nanosciences et de Nanotechnologies（法国国家科学研究中心，纳米科学与技术中心）；Thales Research & Technology (TRT)（泰雷兹研究与技术）；Université de Toulouse, INSA-CNRS-UPS, LPCNO（图卢兹大学，INSA-CNRS-UPS，LPCNO）；Synchrotron SOLEIL（索莱尔同步辐射中心）
Emergence of a weak topological insulator from the Bi$_x$Se$_y$ family and the observation of weak anti-localization
强拓扑绝缘体的发现导致了凝聚态物理的巨大活动和新型拓扑材料的发现。基于铋的硫族化物是示例性强三维拓扑绝缘体，其在所有表面上具有奇数个无质量狄拉克费米子态。一个与这个概念不同的想法是弱拓扑绝缘体，其中只有某些表面终端主机表面状态的特点是偶数狄拉克锥导致令人兴奋的新物理。然而，在实验上，弱拓扑绝缘体已被证明是难以捉摸的。在这里，我们报告发现了一个弱的拓扑绝缘体（WTI），铋硒，铋硫族化物家庭的间接带隙为42毫电子伏。它的结构单元由铋双层（Bi $_2$）组成，铋双层是夹在两个Bi $_2$ Se $_3$单元之间的已知量子自旋霍尔绝缘体，两个Bi $_2$ Se $_3$单元是三维强拓扑绝缘体。角分辨光电子能谱（ARPES）测量和密度泛函理论（DFT）计算证实了BiSe的弱拓扑绝缘态的存在。此外，我们已经进行了磁输运测量单晶片以及薄膜的BiSe，表现出明显的签名弱反本地化在低温下，符合拓扑绝缘体的属性。
Quasi One Dimensional Dirac Electrons on the Surface of Ru$_2$Sn$_3$
利用ARPES方法研究了新型三维强拓扑绝缘体Ru $_2$ Sn $_3$的表面态.与目前已知的3D TI（其显示具有穿过表面布里渊区（SBZ）中的一个点的线性各向同性色散的二维狄拉克锥）相比，Ru $_2$ Sn $_3$上的表面状态是高度各向异性的，显示沿着某些高对称方向的几乎平坦的色散。这导致准一维（1D）狄拉克电子态在整个SBZ，我们认为是继承的Ru $_2$ Sn $_3$的体电子结构中的功能，其中体导带是高度各向异性的。与先前实验表征的TI不同，Ru $_2$ Sn $_3$的拓扑表面态是d-p带反转而不是s-p带反转的结果。所观测到的表面态在拓扑上等价于表面布里渊区的单个2D狄拉克锥
Dabconium hybrid perovskites include a number of recently-discovered ferroelectric phases with large spontaneous polarisations. The origin of ferroelectric response has been rationalised in general terms in the context of hydrogen bonding, covalency, and strain coupling. Here we use a combination of simple theory, Monte Carlo simulations, and density functional theory calculations to assess the ability of these microscopic ingredients---together with the always-present through-space dipolar coupling---to account for the emergence of polarisation in these particular systems whilst not in other …
Young and Kane have given a great insight for 2D Dirac semimetals with nontrivial topology in the presence of nonsymmorphic crystalline symmetry. Based on one of 2D nonsymmorphic square lattice structures they proposed, we further construct a set of 3D minimal tight-binding models via vertically stacking the 2D nonsymmorphic lattice. Specifically, our model provides a platform to generate three topologically semimetallic phases such as Dirac nodal line semimetals, Weyl nodal line semimetals and Weyl semimetals. The off-centered mirror symmetry sufficiently protects nodal lines emerging within …
In this letter, we predict the emergence of non-trivial band topology in the family of XX'Bi compounds having $P\overline{6}2m$ (\# 189) space group. Using first principles calculations within hybrid functional framework, we demonstrate that NaSrBi and NaCaBi are strong topological insulator under controlled band engineering. Here, we propose three different ways to engineer the band topology to get a non-trivial order: (i) hydrostatic pressure, (ii) biaxial strain (due to epitaxial mismatch), and (iii) doping. Non-triviality is confirmed by investigating bulk band inversion, topological Z$_2$…
Realization of a parity-violating antiferromagnetic state in LaMnSi
Graduate School of Advanced Science and Engineering, Hiroshima University（广岛大学先进理工学研究科）；International Institute for Sustainability with Knotted Chiral Meta Matter (WPI-SKCM 2 ), Hiroshima University（广岛大学螺旋手性超物质可持续研究所（WPI-SKCM2））；Department of Chemical System Engineering, Graduate School of Engineering, The University of Tokyo（东京大学大学院工学系研究科化学系统工程专业）；Research Institute for Synchrotron Radiation Science, Hiroshima University（广岛大学同步辐射科学研究所以）；Japan Synchrotron Radiation Research Instit（日本同步辐射研究机构）
The contribution of bulk and surface to the electrical resistance along crystallographic \textit{b}- and \textit{c}-axes as a function of crystal thickness gives evidence for a temperature independent surface states in an antiferromagnetic narrow-gap semiconductor CrSb$_{2}$. ARPES shows a clear electron-like pocket at $Γ$-$Z$ direction which is absent in the bulk band structure. First-principles calculations also confirm the existence of metallic surface states inside the bulk gap. Whereas combined experimental probes point to enhanced surface conduction similar to topological insulators, sur…
Using spin- and angle- resolved photoemission spectroscopy (spin-ARPES) together with ${\it ab~initio}$ calculations, we demonstrate the existence of a type-II Dirac semimetal state in NiTe$_2$. We show that, unlike PtTe$_2$, PtSe$_2$, and PdTe$_2$, the Dirac node in NiTe$_2$ is located in close vicinity of the Fermi energy. Additionally, NiTe$_2$ also hosts a pair of band inversions below the Fermi level along the $Γ-A$ high-symmetry direction, with one of them leading to a Dirac cone in the surface states. The bulk Dirac nodes and the ladder of band inversions in NiTe$_2$ support unique topo…
Carbon allotropes have a large family of materials with varieties of crystal structures and properties and can realize different topological phases. Using first principles calculations, we predict a new two-dimensional (2D) carbon allotrope, namely penta-octa-graphene, which consists of pentagonal and octagonal carbon rings. We find that penta-octa-graphene can host both type-I and type-II Dirac line nodes (DLNs). The band inversion between conduction and valence bands forms the type-I DLNs and the two highest valence bands form the type-II DLNs. We find that the type-I DLNs are robust to the …
Topological properties of systems lead to the emergence of surface states which can be observed experimentally within the angle-resolved photoemission spectroscopy (ARPES) measurements. Recently, the topological properties of Pb$_{2}$Pd were reported. In this paper, we discuss the role of the surface termination on the realized surface states. We discuss the termination dependence of the surface state for (001) and (110) surface. We demonstrate that the Pd terminated (001) surface allow realization of the Dirac cone-like surface state. In the case (110) we observe well visible surface states w…
Relativistic and nonrelativistic spin splitting above and below the Fermi level in a $g$-wave altermagnet
Lawrence Berkeley National Lab（劳伦斯伯克利国家实验室）；University of California, Berkeley（加州大学伯克利分校）；University of Notre Dame（圣母大学）；Carnegie Mellon University（卡内基梅隆大学）
The topological Hall effect (THE) has been discovered in ultrathin SrRuO3 (SRO) films, where the interface between the SRO layer and another oxide layer breaks the inversion symmetry resulting in the appearance of THE. Thus, THE only occurs in ultra-thin SRO films of several unit cells. In addition to employing a heterostructure, the inversion symmetry can be broken intrinsically in bulk SRO by introducing defects. In this study THE is observed in 60 nm thick SRO films, in which defects and lattice distortions are introduced by helium ion irradiation. The irradiated SRO films exhibit a pronoun…
Optical evidence of surface state suppression in Bi based topological insulators
凝聚态研究的一个关键挑战是拓扑绝缘体（TI）化合物的优化，以研究其独特的表面状态和未来的应用。真正绝缘的体态将允许利用预测的表面态性质，如防止反向散射，无耗散的自旋极化电流，以及新粒子的出现。为此，最近取得了重大进展，引入了高电阻的Bi $_2$ Te $_2$ Se，其中在低温下观察到表面态电导和量子振荡。然而，一个悬而未决的关键问题仍然存在：虽然室温ARPES研究揭示了TI表面状态的明确证据，但它们在运输实验中的观察仅限于低温。更好地理解这种表面态抑制在高温下是根本的利益，并推动设备应用的边界向室温操作至关重要。在这项工作中，我们同时测量TI体和表面状态，通过温度相关的光学光谱，结合运输和ARPES测量。我们发现在低温下相干表面态输运的证据，并提出声子介导的体和表面态之间的耦合抑制表面电导随着温度的升高。
Realization of Quantum Spin Hall State in Monolayer 1T'-WTe2
量子自旋霍尔（QSH）绝缘体是一种新型的二维量子态物质，在没有磁场的情况下具有量子化的霍尔电导，这是由于拓扑保护的无耗散边缘态桥接了由带反转和强自旋轨道耦合打开的能隙。通过使用角分辨光电子能谱（ARPES）和第一性原理计算研究外延生长的单层1 T '-WTe 2的电子结构，我们观察到清晰的拓扑带反转和带隙开放的特征，这是QSH态的标志。扫描隧道显微镜测量进一步证实了正确的晶体结构和体带隙的存在，并提供了证据的修改后的电子结构附近的边缘，这是一致的预期QSH绝缘体。我们的研究结果建立了单层1 T '-WTe 2作为一个强大的二维过渡金属二硫属化物（TMDC）材料家族中的一个新的类QSH绝缘体具有大的带隙。
The Weyl semimetal MoTe$_2$ offers a rare opportunity to study the interplay between Weyl physics and superconductivity. Recent studies have found that Se substitution can boost the superconductivity up to 1.5K, but suppress the Td structure phase that is essential for the emergence of Weyl state. A microscopic understanding of possible coexistence of enhanced superconductivity and the Td phase has not been established so far. Here, we use scanning tunneling microscopy (STM) to study a optimally doped new superconductor MoTe$_{1.85}$Se$_{0.15}$ with bulk Tc ~ 1.5K. By means of quasiparticle in…
X-ray diffraction pressure studies at room temperature demonstrate that the spinel FeAl$_{2}$O$_{4}$ transforms to a tetragonal phase at ~18 GPa. This tetragonal phase has a highly irregular unit-cell volume versus pressure dependence up to ~45 GPa, after which a transformation to a Cmcm post-spinel phase is onset. This is attributable to pressure driven Fe-Al site inversion at room temperature, corroborated by signatures in the 57Fe Mössbauer spectroscopy pressure data. At the tetragonal to post-spinel transition, onset in the range 45-50 GPa, there is a concurrent emergence of a non-magnetic…
Thin Bi films are interesting candidates for spintronic applications due to a large spin-orbit splitting that, combined with the loss of inversion symmetry at the surface, results in a band structure that is not spin-degenerate. In recent years, applications for topological insulators based on Bi and Bi alloys have as well attracted much attention. Here we present ARPES studies of Bi/InAs(100) interface. Bismuth deposition followed by annealing of the surface results in the formation of one full Bi monolayer decorated by Bi-nanolines. We found that the building up of the interface does affect …
In magnetic topological insulators (TIs), the interplay between magnetic order and nontrivial topology can induce fascinating topological quantum phenomena, such as the quantum anomalous Hall effect, chiral Majorana fermions and axion electrodynamics. Recently, a great deal of attention has been focused on the intrinsic magnetic TIs, where disorder effects can be eliminated to a large extent, which is expected to facilitate the emergence of topological quantum phenomena. In despite of intensive efforts, experimental evidence of the topological surface states (SSs) remains elusive. Here, by com…
