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

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 Γ.