Origin of topologically trivial states and topological phase transitions in low-buckled plumbene

TL;DR

This study combines theoretical models and first-principles calculations to analyze the electronic and topological properties of low-buckled plumbene, revealing its trivial topological nature and potential for quantum anomalous Hall and spin Hall effects.

Contribution

It demonstrates that coupling between topological states causes plumbene's trivial topology and explores how functionalization induces quantum spin Hall effects.

Findings

Low-buckled plumbene is a topologically trivial insulator.

Exchange fields can induce quantum anomalous Hall effects with Chern numbers ±2.

Functionalization with ethynyl leads to quantum spin Hall effects.

Abstract

Combining tight-binding (TB) models with first-principles calculations, we investigate electronic and topological properties of plumbene. Different from the other two-dimensional (2D) topologically nontrivial insulators in group IVA (from graphene to stanene), low-buckled plumbene is a topologically trivial insulator. The plumbene without spin-orbit coupling exhibits simultaneously two kinds of degeneracies, i.e., quadratic non-Dirac and linear Dirac band dispersions around the \Gamma and K/K' points, respectively. Our TB model calculations show that it is the coupling between the two topological states around the \Gamma and K/K' points that triggers the global topologically trivial property of plumbene. Quantum anomalous Hall effects with Chern numbers of 2 or -2 can be, however, achieved after an exchange field is introduced. When the plumbene is functionalized with ethynyl (PbC2H), quantum spin Hall effects appear due to the breaking of the coupling effect of the local topological states.