Photo-magnetization in two-dimensional sliding ferroelectrics

Jian Zhou

doi:10.1038/s41699-022-00297-6

Abstract

Light–matter interaction is one of the key routes to understanding and manipulating geometric and electronic behaviors of materials, especially two-dimensional materials which are optically accessible owing to their high surface to volume ratio. In the current work, we focus on the recently discovered two-dimensional sliding ferroelectric materials, in which the out-of-plane electric polarization can be switched with a small horizontal translation in one layer. Combining symmetry analysis and first-principles calculations, we predict that light illumination could inject non-equilibrium magnetic moments into the sliding ferroelectrics. Such magnetic moment is composed of both spin and orbital degrees of freedom contributions. We use ZrI2, WTe2, and MoS2 bilayer ferroelectrics to illustrate our theory. Under intermediate light illumination, one can yield non-equilibrium magnetic moments on the order of 0.1–1 μB in these systems, which also depends on the polarization nature of incident light. Furthermore, we show that such photo-injected magnetism changes its sign when the sliding dipole moment switches. This photo-magnetization can be detected by magneto-optical methods (such as Kerr or Faraday effect), which serves as an indicator of sliding ferroelectricity. Hence, one can use an all-optical pump and probe setup to measure and detect the subtle sliding ferroelectric phase.

Highlights

Two-dimensional (2D) ferroelectric materials hold their potential applications in ultrafast information storage and data memory with low energy cost and high volumetric density[1–3]
Most 2D sub-nanometer ferroelectric materials have been realized by physically exfoliating layered materials into their monolayer form, which lacks inversion symmetry intrinsically and possesses an in-plane electric polarization or out-of-plane dipole moment
One has to note that this photo-magnetization is non-equilibrium angular momentum injection, which is different from spin polarization created by a static magnetic field in equilibrium

Summary

INTRODUCTION

Two-dimensional (2D) ferroelectric materials hold their potential applications in ultrafast information storage and data memory with low energy cost and high volumetric density[1–3]. The calculations suggest that linearly polarized light (LPL) induced bulk photovoltaic effect, namely, shift current would flip its direction once the SFE transition occurs in the trilayer WTe2, while the bilayer structure does not have such property[27]. In order to distinguish the subscript between the LPL and CPL, we use ↺ and ↻ to denote the left-handed and right-handed CPL (instead of subscripts xy and yx in ξ), RESULTS Nonlinear Edelstein theory for photo-magnetization respectively Since both spin and orbital are angular momenta, they show the same symmetry transformation under mirror M, rotation C, and time reversal T. The complex conjugate of electric field is EÃðωÞ 1⁄4 EðÀωÞ This equation explicitly indicates that under a two-photon (polarization along b and c respectively) process with opposite phase, the system could generate magnetization hδmai which points along direction-a. The angular momentum O transforms as pseudovector, npj 2D Materials and Applications (2022) 15

Zhou 3

DISCUSSION

METHODS