Bi1Te1 is a dual topological insulator

Abstract

New three-dimensional (3D) topological phases can emerge in superlattices containing constituents of known two-dimensional topologies. Here we demonstrate that stoichiometric Bi1Te1, which is a natural superlattice of alternating two Bi2Te3 quintuple layers and one Bi bilayer, is a dual 3D topological insulator where a weak topological insulator phase and topological crystalline insulator phase appear simultaneously. By density functional theory, we find indices (0;001) and a non-zero mirror Chern number. We have synthesized Bi1Te1 by molecular beam epitaxy and found evidence for its topological crystalline and weak topological character by spin- and angle-resolved photoemission spectroscopy. The dual topology opens the possibility to gap the differently protected metallic surface states on different surfaces independently by breaking the respective symmetries, for example, by magnetic field on one surface and by strain on another surface.

Intrinsically Low Thermal Conductivity and High Carrier Mobility in Dual Topological Quantum Material, n‐Type BiTe

“…BiTe, like its topological cousin BiSe, exhibits inverted a band structure between the valence band (which consisted majorly by 5p orbitals of Te, Figure S3) and conduction bands (mainly consisting of 6p orbitals of Bi QL, Figure S3) around the Fermi level along the Γ–A line in the Brillouin zone. This band inversion is induced by the SOC . Due to the relatively stronger SOC in BiTe (Te being heavier than Se), the energy difference between the inverted bands increases, giving rise to a larger band gap in BiTe.…”

“…BiTe, a unique member of the (Bi 2 ) m (Bi 2 Te 3 ) n (where m : n =1:2) homologous series, possesses natural van der Waals hetero‐structure (space group ), where a zigzag Bi‐Bi bilayer is sandwiched between Te‐Bi‐Te‐Bi‐Te quintuple layers (QL) via weak van der Waals interactions (Figure a). Recently, BiTe has emerged as a dual topological insulator, which is a fascinating new quantum material . Herein, both the weak topological insulator (WTI) and topological crystalline insulator (TCI) phases coexist.…”

“…Such unique crystal and electronic structure of BiTe stimulate enough interest to investigate its thermal conductivity and electronic properties. Although, both Bi 2 Te 3 and BiTe belong to the same (Bi 2 ) m (Bi 2 Te 3 ) n homologous series, Bi 2 Te 3 is a well‐known experimentally established 3D TI and TE materials, but BiTe is a dual topological insulator (WTI and TCI phases) with no detailed fundamental understanding of its TE properties.…”

Robust dual topological character with spin-valley polarization in a monolayer of the Dirac semimetal Na3Bi

“…In the presence of crystal mirror symmetry, the coexistence of TI and TCI phases has been predicted in three dimensions for Bi 1−x Sb x [6] and Bi chalcogenides [7][8][9], and thus they exhibit a dual topological character (DTC). Recently, unusual topological surface states for a three-dimensional (3D) DTC system have been observed experimentally [8,9]. In the 2D case, graphene may be a prototypical example of a DTC [10,11].…”

“…The hallmark of a TCI, similar to a TI, is the presence of gapless surface/edge states with Dirac points inside of the insulating bulk energy gap. In the presence of crystal mirror symmetry, the coexistence of TI and TCI phases has been predicted in three dimensions for Bi 1−x Sb x [6] and Bi chalcogenides [7][8][9], and thus they exhibit a dual topological character (DTC). Recently, unusual topological surface states for a three-dimensional (3D) DTC system have been observed experimentally [8,9].…”