Switchable and unswitchable bulk photovoltaic effect in two-dimensional interlayer-sliding ferroelectrics

TL;DR

This paper investigates the unique bulk photovoltaic effects in 2D interlayer sliding ferroelectrics, revealing switchable out-of-plane and unswitchable in-plane BPVE properties validated by symmetry analysis and first-principles calculations.

Contribution

It uncovers the coexistence of switchable and unswitchable BPVE in 2D ferroelectrics due to interlayer sliding, expanding understanding of ferroelectricity and photovoltaic effects.

Findings

Out-of-plane BPVE is switchable with ferroelectric polarization.

In-plane BPVE remains unswitchable despite ferroelectric flipping.

Symmetry analysis explains the distinct BPVE behaviors.

Abstract

Spontaneous polarization and bulk photovoltaic effect (BPVE) are two concomitant physical properties in ferroelectric materials. The flipping of ferroelectric order usually accompanies with the switching of BPVE as both of them are reversed under the inversion symmetry. In this study, we report the distinctive BPVE characters in two-dimensional (2D) interlayer sliding ferroelectric materials featuring unswitchable in-plane BPVE (light-induced photocurrent in the xy plane) and switchable out-of-plane BPVE (light-induced polarization along the z-direction). Symmetry analysis within abstract bilayer crystal model and first-principles calculations validate these BPVE properties. It is because the positive and negative ferroelectric states caused by interlayer sliding are related by mirror symmetry which cannot flip all the BPVE tensor elements. This finding extends the understanding of the relationship between ferroelectricity and BPVE. On one hand, the switchable out-of-plane BPVE can be used to design switchable photoelectric devices. On the other hand, the in-plane BPVE is robust against the ferroelectric flipping, and the unswitchable character is beneficial to construct larger-scale photoelectric devices.