Elemental Ferroelectric Topological Insulator in $\psi$-bismuthene

TL;DR

This paper introduces $ extpsi$-bismuthene, a novel 2D elemental ferroelectric topological insulator with unique properties like measurable polarization, nontrivial band gap, and auxetic behavior, opening new avenues in physics and technology.

Contribution

It proposes the first 2D elemental ferroelectric quantum spin Hall insulator, $ extpsi$-bismuthene, with measurable ferroelectricity and topological properties, expanding the scope of ferroelectric topological insulators.

Findings

$ extpsi$-bismuthene exhibits measurable ferroelectric polarization.

It has a nontrivial band gap with a moderate switching barrier.

Displays all-angle auxetic behavior with giant negative Poisson's ratio.

Abstract

Ferroelectric quantum spin Hall insulator (FEQSHI) exhibits coexisting ferroelectricity and time-reversal symmetry protected edge states, holding fascinating prospects for inviting both scientific and application advances, especially in two dimensions. However, all of the previously demonstrated FEQSHIs consist two or more constituent elements. We herein propose the $\psi$-bismuthene, an uncharted allotrope of bilayer Bi (110), to be the first example of 2D elemental FEQSHI. It is demonstrated that $\psi$-bismuthene harbors measurable ferroelectric polarization and nontrivial band gap with moderate switching barrier, which are highly beneficial for the detection and observation of the ferroelectric topologically insulating states. In addition, all-angle auxetic behavior with giant negative Poisson's ratio and ferroelectric controllable persistent spin helix in $\psi$-bismuthene are also discussed. The emergent elemental FEQSHI represents a novel domain for both fundamental physics and technological innovation.