Gate-tunable imbalanced Kane-Mele model in encapsulated bilayer jacutingaite

TL;DR

This study investigates how encapsulation and electric fields can induce topological phases in bilayer jacutingaite, revealing a tunable transition from trivial insulator to quantum spin Hall state driven by sublattice symmetry effects.

Contribution

It introduces a minimal imbalanced Kane-Mele model to explain the electric-field-induced topological transition in encapsulated bilayer jacutingaite, highlighting the role of sublattice imbalance and symmetry breaking.

Findings

Encapsulation results in a small trivial gap due to sublattice effects.

A small electric field induces a transition to a quantum spin Hall insulator.

The transition is well-described by an imbalanced Kane-Mele model.

Abstract

We study free, capped and encapsulated bilayer jacutingaite Pt$_2$HgSe$_3$ from first principles. While the free standing bilayer is a large gap trivial insulator, we find that the encapsulated structure has a small trivial gap due to the competition between sublattice symmetry breaking and sublattice-dependent next-nearest-neighbor hopping. Upon the application of a small perpendicular electric field, the encapsulated bilayer undergoes a topological transition towards a quantum spin Hall insulator. We find that this topological transition can be qualitatively understood by modeling the two layers as uncoupled and described by an imbalanced Kane-Mele model that takes into account the sublattice imbalance and the corresponding inversion-symmetry breaking in each layer. Within this picture, bilayer jacutingaite undergoes a transition from a 0+0 state, where each layer is trivial, to a 0+1 state, where an unusual topological state relying on Rashba-like spin orbit coupling emerges in only one of the layers.