Chemically induced large-gap quantum anomalous Hall insulator states in III-Bi honeycombs

Christian P Crisostomo,Feng-Chuan Chuang,Arun Bansil,Chia-Hsiu Hsu,Hsin Lin,Zhi-Quan Huang

doi:10.1038/s41524-017-0044-9

Abstract

The search for novel materials with new functionalities and applications potential is continuing to intensify. Quantum anomalous Hall (QAH) effect was recently realized in magnetic topological insulators (TIs) but only at extremely low temperatures. Here, based on our first-principles electronic structure calculations, we predict that chemically functionalized III-Bi honeycombs can support large-gap QAH insulating phases. Specifically, we show that functionalized AlBi and TlBi films harbor QAH insulator phases. GaBi and InBi are identified as semimetals with non-zero Chern number. Remarkably, TlBi exhibits a robust QAH phase with a band gap as large as 466 meV in a buckled honeycomb structure functionalized on one side. Furthermore, the electronic spectrum of a functionalized TlBi nanoribbon with zigzag edge is shown to possess only one chiral edge band crossing the Fermi level within the band gap. Our results suggest that III-Bi honeycombs would provide a new platform for developing potential spintronics applications based on the QAH effect.

Highlights

Unlike the quantum Hall state, which relies on the presence of an external magnetic field, the quantum anomalous Hall (QAH) state is realized through the effects of intrinsic spin-orbit coupling (SOC) and intrinsic magnetization in a material.[11]
Crystal structure of the 2D III elements with Bi (III-Bi) honeycomb with adsorbed N and H atoms on the III-element and Bi sites [denoted as III-BiNH, Case I] and the related first Brillouin zone (BZ) with high-symmetry points are presented in Fig. 1, along with sideviews of the two-sided and one-sided functionalized planar (PL), buckled (BK), and inversely buckled (IBK) III-BiNH
Focusing on combinations of group III elements with Bi (III-Bi), which assume the quantum spin Hall (QSH) state over a range of lattice constants, we present in Table 1 the equilibrium lattice constant for the PL honeycomb, along with the associated total energies, system band gaps and topological invariants (C ≠ 0 implies QAH state) for both cases I and II

Summary

Introduction

Two-dimensional (2D) topological materials have continued to gain increasing attention in the recent years.[1,2,3,4] Among the large variety of possible topological phases, quantum anomalous Hall (QAH) insulators[5] have drawn special interest since the QAH state, which supports chiral edge states, is highly suited for spintronics and low-power-consumption electronic applications.[6,7,8,9,10] Unlike the quantum Hall state, which relies on the presence of an external magnetic field, the QAH state is realized through the effects of intrinsic spin-orbit coupling (SOC) and intrinsic magnetization in a material.[11]. In addition to the magnetic topological crystalline insulators,[30,31] films of elements of groups IV16 and V32–34 have been predicted to harbor the QAH phases. It has been predicted that III–V films can support the QSH state in a number of freestanding[24] and functionalized cases,[25,26,28] only limited work has been reported toward the QAH phase[35] with relatively small band gaps (~105 meV).

Results

Conclusion