Twist-resilient and robust ferroelectric quantum spin Hall insulators driven by van der Waals interactions

TL;DR

This paper proposes a robust, room-temperature ferroelectric control of quantum spin Hall insulators in 2D heterostructures, enabling non-volatile topological switching via van der Waals interactions.

Contribution

It introduces a novel heterostructure design combining ferroelectric and trivial insulator layers to achieve switchable topological phases with enhanced stability.

Findings

The heterostructure switches between trivial and topological phases upon polarization reversal.

The topological band gap is mediated by interlayer hybridization and spin-orbit coupling.

The effect persists at room temperature and is resilient to layer orientation.

Abstract

Quantum spin Hall insulators (QSHI) have been proposed to power a number of applications, many of which rely on the possibility to switch on and off the non-trivial topology. Typically this control is achieved through strain or external electric fields, which require energy consumption to be maintained. On the contrary, a non-volatile mechanism would be highly beneficial and could be realized through ferroelectricity if opposite polarization states are associated with different topological phases. While this is not possible in a single ferroelectric material where the two polarization states are related by inversion, the necessary asymmetry could be introduced by combining a ferroelectric layer with another two-dimensional (2D) trivial insulator. Here, by means of first-principles simulations, not only we propose that this is a promising strategy to engineer non-volatile ferroelectric control of topological order in 2D heterostructures, but also that the effect is robust and can survive up to room temperature, irrespective of the weak van der Waals coupling between the layers. We illustrate the general idea by considering a heterostructure made of a well-known ferroelectric material, In$_2$Se$_3$, and a suitably chosen, easily exfoliable trivial insulator, CuI. In one polarization state the system is trivial, while it becomes a QSHI with a robust band gap upon polarization reversal. Remarkably, the topological band gap is mediated by the interlayer hybridization and allows to maximise the effect of intralayer spin-orbit coupling, promoting a robust ferroelectric topological phase that could not exist in monolayer materials and is resilient against relative orientation and lattice matching between the layers.