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

Quantum spin Hall insulators 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 polarizations are associated with different topological phases. While this is not possible in a single ferroelectric material owing to symmetry constraints, the necessary asymmetry could be introduced by combining a ferroelectric layer with another 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. Remarkably, the topological band gap is mediated by the interlayer hybridization and allows to maximise the effect of on-site 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.