A topological Dirac insulator in a quantum spin Hall phase : Experimental observation of first strong topological insulator

Abstract

When electrons are subject to a large external magnetic field, the conventional charge quantum Hall effect \cite{Klitzing,Tsui} dictates that an electronic excitation gap is generated in the sample bulk, but metallic conduction is permitted at the boundary. Recent theoretical models suggest that certain bulk insulators with large spin-orbit interactions may also naturally support conducting topological boundary states in the extreme quantum limit, which opens up the possibility for studying unusual quantum Hall-like phenomena in zero external magnetic field. Bulk Bi${}_{1-x}$Sb${}_x$ single crystals are expected to be prime candidates for one such unusual Hall phase of matter known as the topological insulator. The hallmark of a topological insulator is the existence of metallic surface states that are higher dimensional analogues of the edge states that characterize a spin Hall insulator. In addition to its interesting boundary states, the bulk of Bi${}_{1-x}$Sb${}_x$ is predicted to exhibit three-dimensional Dirac particles, another topic of heightened current interest. Here, using incident-photon-energy-modulated (IPEM-ARPES), we report the first direct observation of massive Dirac particles in the bulk of Bi${}_{0.9}$Sb${}_{0.1}$, locate the Kramers' points at the sample's boundary and provide a comprehensive mapping of the topological Dirac insulator's gapless surface modes. These findings taken together suggest that the observed surface state on the boundary of the bulk insulator is a realization of the much sought exotic "topological metal". They also suggest that this material has potential application in developing next-generation quantum computing devices.

16 pages, 3 Figures. Submitted to NATURE on 25th November(2007)

References in corpus (5)

• Quantum Spin Hall Insulator State in HgTe Quantum Wells
• Room-Temperature Quantum Hall Effect in Graphene
• Substrate-induced band gap opening in epitaxial graphene
• Phase transition between the quantum spin Hall and insulator phases in 3D: emergence of a topological gapless phase
• Signatures of Electron Fractionalization in Ultraquantum Bismuth

Cited by in corpus (22)

• Discovery (theoretical prediction and experimental observation) of a large-gap topological-insulator class with spin-polarized single-Dirac-cone on the surface
• Anderson Transitions
• First direct observation of Spin-textures in Topological Insulators : Spin-resolved ARPES as a probe of topological quantum spin Hall effect and Berry's phase
• Topological Surface States Protected From Backscattering by Chiral Spin Texture
• Electrically detected interferometry of Majorana fermions in a topological insulator
• Topological Anderson Insulator
• Helical Metal Inside a Topological Band Insulator
• Exciton condensation and charge fractionalization in a topological insulator film
• Fractional Quantum Hall Effect via Holography: Chern-Simons, Edge States, and Hierarchy
• Orbital analogue of quantum anomalous Hall effect in $p$-band systems
• Topology induced anomalous defect production by crossing a quantum critical point
• Universal phase diagrams for the quantum spin Hall systems
• Electronic Structures and Surface States of Topological Insulator Bi${}_{1-x}$Sb${}_x$
• Topological Insulators and Metals in Atomic Optical Lattices
• A $\Gamma$-matrix generalization of the Kitaev model
• Lattice model of three-dimensional topological singlet superconductor with time-reversal symmetry
• Finite difference method for transport properties of massless Dirac fermions
• Coherent Oscillations and Giant Edge Magnetoresistance in Singly Connected Topological Insulators
• Signatures of surface states in bismuth at high magnetic fields
• DMPK Equation for the Edge Transport of Quantum Spin Hall Insulator
• A Z${}_2$ index of Dirac operator with time reversal symmetry
• First observation of spin-helical Dirac fermions and topological phases in undoped and doped Bi2Te3 demonstrated by spin-ARPES spectroscopy