Anisotropic Topological Surface States on High‐Index Bi₂Se₃ Films

Abstract

A high-index topological insulator thin film, Bi2 Se3 (221), is grown on a faceted InP(001) substrate by molecular-beam epitaxy (see model in figure (a)). Angle-resolved photoemission spectroscopy measurement reveals the Dirac cone structure of the surface states on such a surface (figure (b)). The Fermi surface is elliptical (figure (c)), suggesting an anisotropy along different crystallographic directions. Transport studies also reveal a strong anisotropy in Hall conductance.

Strain in epitaxial high-index Bi2Se3(221) films grown by molecular-beam epitaxy

“…Such a film is like a pile of weakly coupled QL slabs stacked side-by-side on substrate, which can be more tolerable to strain even than that of a covalent crystal. In the earlier experiment using InP as the substrate, 20 strain was not of primary concern and there was little lattice misfit between the deposit and substrate in the a-axis direction. Here in this work, we report growth of strained Bi2Se3(221) on In2Se3-buffered GaAs(001) substrate and note a much retarded strain-relaxation dynamics.…”

“…18,19 Such elliptical Dirac cone has been experimentally revealed also by angle-resolved photoelectron spectroscopy measurements. 20 The group velocity…”

“…25 In an early experiment, we demonstrated successful growth of high-index Bi2Se3(221) epifilm by molecularbeam epitaxy (MBE) on purposely roughened InP(001) substrate. 20 The off c-axis growth direction of Bi2Se3 occurred because of the epitaxial relation (111) Bi Fig. 1(d)].…”

Molecular Beam Epitaxial Growth and Properties of Bi2Se3 Topological Insulator Layers on Different Substrate Surfaces

“…Bi 2 Se 3 on InP(001) has been successfully grown by MBE, furnishing Bi 2 Se 3 (221), 26 and by hot-well epitaxy 27 furnishing the (001) orientation. In this case we grew a ZnCdSe buffer to improve the chemical compatibility between the substrate and the TI, on the basis of similar work which used a ZnSe buffer on GaAs(111)B.…”

Role of surface termination in realizing well-isolated topological surface states within the bulk band gap inTlBiSe2andTlBiTe2

“…Unlike the (111) surface, however, the in-plane lattice constants for the (221) surface are unequal (a = 4.32Å and b = 10.06Å), reducing the symmetry to a single yz mirror plane, instead of the three-fold rotation plus a mirror plane symmetry of the (111) surface. 46,47 The (221) surface thus has a strong anisotropy between the x and y directions, which are symmetric for the (111) surface. Band structure of a symmetric TlBiSe 2 slab composed of 111 atomic layers with a flat (221) surface is shown in Fig.…”