Elemental topological ferroelectrics and polar metals of few-layer materials

TL;DR

This paper predicts new two-dimensional elemental ferroelectric and polar metallic materials with topological properties, created through stacking-engineering of buckled honeycomb lattices, expanding the possibilities for 2D ferroelectric and metallic materials.

Contribution

It introduces a theoretical framework for designing 2D elemental topological ferroelectrics and polar metals via stacking-engineering of buckled honeycomb structures.

Findings

Two-bilayer Bi film is an elemental topological ferroelectric.

Bi films with 3-4 bilayers are ferroelectric-like polar metals with topological edge states.

Trivial elemental polar metals are predicted for Ge and Sn.

Abstract

Ferroelectricity can exist in elemental phases as a result of charge transfers between atoms occupying inequivalent Wyckoff positions. We investigate the emergence of ferroelectricity in two-dimensional elemental materials with buckled honeycomb lattices. Various multi-bilayer structures hosting ferroelectricity are designed by stacking-engineering. Ferroelectric materials candidates formed by group IV and V elements are predicted theoretically. Ultrathin Bi films show layer-stacking-dependent physical properties of ferroelectricity, topology, and metallicity. The two-bilayer Bi film with a polar stacking sequence is found to be an elemental topological ferroelectric material. Three and four bilayers Bi films with polar structures are ferroelectric-like elemental polar metals with topological nontrivial edge states. For Ge and Sn, trivial elemental polar metals are predicted. Our work reveals the possibility of design two-dimensional elemental topological ferroelectrics and polar metals by stacking-engineering.