Two-dimensional Topological Ferroelectric Metal with Giant Shift Current

TL;DR

This paper demonstrates through first-principles calculations that a monolayer PtBi2 is an intrinsic 2D topological ferroelectric metal with giant shift current, combining ferroelectricity, metallicity, and nontrivial topology for advanced optoelectronic applications.

Contribution

It provides the first evidence of a 2D topological ferroelectric metal with giant shift current, revealing a new class of materials with combined ferroelectric, metallic, and topological properties.

Findings

PtBi2 monolayer is an intrinsic 2D topological ferroelectric metal.

It exhibits a significant bulk photovoltaic effect enhanced by strain.

The material has a Z2 topological invariant of 1, indicating nontrivial topology.

Abstract

The pursuit for "ferroelectric metal" which combines seemingly incompatible spontaneous electric polarization and metallicity, has been assiduously ongoing but remains elusive. Unlike traditional ferroelectrics with a wide band gap, ferroelectric (FE) metals can naturally incorporate nontrivial band topology near the Fermi level, endowing them with additional exotic properties. Here, we show first-principles evidence that the metallic PtBi2 monolayer is an intrinsic two-dimensional (2D) topological FE metal, characterized by out-of-plane polarization and a moderate switching barrier. Moreover, it exhibits a topologically nontrivial electronic structure with Z2 invariant equal to 1, leading to a significant FE bulk photovoltaic effect. A slight strain can further enhance this effect to a remarkable level, which far surpass that of previously reported 2D/3D FE materials. Our work provides an important step towards realizing intrinsic monolayer topological FE metals and paves a promising way for future nonlinear optical devices.