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 metallicPtBi2monolayer 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 withℤ2invariant 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 surpasses that of previously reported 2D and 3D FE materials. Our Letter provides an important step toward realizing intrinsic monolayer topological FE metals and paves a promising way for future nonlinear optical devices.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.186801