Twisted Type-II Rashba Homobilayer: A Platform for Tunable Topological Flat Bands

TL;DR

This paper introduces twisted type-II Rashba homobilayers as a new platform for tunable topological flat bands, demonstrating their potential for controlling topological phases through twist angle and material parameters.

Contribution

It proposes a novel twisted Rashba homobilayer system that enables tunable topological flat bands and topological phase transitions, expanding the possibilities for topological material engineering.

Findings

Prediction of flat topological bands with bandwidth below 20 meV.

Identification of a transition from valley Hall to quantum spin Hall insulator with increasing twist angle.

Demonstration of tunability via Rashba spin-orbit coupling and interlayer interactions.

Abstract

The recent discovery of topological flat bands in twisted transition metal dichalcogenide homobilayers and multilayer graphene has sparked significant research interest. We propose a new platform for realizing tunable topological moire flat bands: twisted type-II Rashba homobilayers. The interplay between Rashba spin-orbit coupling and interlayer interactions generates an effective pseudo-antiferromagnetic field, opening a gap within the Dirac cone with non-zero Berry curvature. Using twisted BiTeI bilayers as an example, we predict the emergence of flat topological bands with a remarkably narrow bandwidth (below 20 meV). Notably, the system undergoes a transition from a valley Hall insulator to a quantum spin Hall insulator as the twisting angle increases. This transition arises from a competition between the twisting-driven effective spin-orbit coupling and sublattice onsite energies presented in type-II Rashba moir\'e structures. The high tunability of Rashba materials in terms of the spin-orbit coupling strength, interlayer interaction, and twisting angle expands the range of materials suitable for realizing and manipulating correlated topological properties.