Large-gap quantum anomalous Hall states induced by functionalizing buckled Bi-III monolayer/Al$_{2}$O$_{3}$

TL;DR

This study predicts large-gap quantum anomalous Hall states in Bi-III monolayers on Al$_{2}$O$_{3}$ substrates, achieved through nitrogen passivation and Zeeman splitting, promising for robust quantum and spintronic applications.

Contribution

It introduces a novel approach to realize large-gap QAH states in Bi-III monolayers on Al$_{2}$O$_{3}$ substrates via nitrogen passivation and effective modeling.

Findings

Large topological gap in Bi-III/Al$_{2}$O$_{3}$ system.

Topological phase transition induced by Zeeman splitting.

Effective p_x, p_y orbital model applicable to similar systems.

Abstract

Chiral edge modes inherent to the topological quantum anomalous Hall (QAH) effect are a pivotal topic of contemporary condensed matter research aiming at future quantum technology and application in spintronics. A large topological gap is vital to protecting against thermal fluctuations and thus enabling a higher operating temperature. From first-principle calculations, we propose Al$_{2}$O$_{3}$ as an ideal substrate for atomic monolayers consisting of Bi and group-III elements, in which a large-gap quantum spin Hall effect can be realized. Additional half-passivation with nitrogen then suggests a topological phase transition to a large-gap QAH insulator. By effective tight-binding modelling, we demonstrate that Bi-III monolayer/Al$_{2}$O$_{3}$ is dominated by $p_{x}, p_{y}$ orbitals, with subdominant $p_z$ orbital contributions. The topological phase transition into the QAH is induced by Zeeman splitting, where the off-diagonal spin exchange does not play a significant role. The effective model analysis promises utility far beyond Bi-III monolayer/Al$_{2}$O$_{3}$, as it should generically apply to systems dominated by $p_{x}, p_{y}$ orbitals with a band inversion at $\Gamma$.