Pure Bulk Orbital and Spin Photocurrent in Two-Dimensional Ferroelectric Materials

TL;DR

This paper explores how light can induce orbital and spin currents in two-dimensional ferroelectric materials, revealing new mechanisms for controlling electronic, orbital, and spin transport in nanoscale devices.

Contribution

It introduces a theoretical framework for bulk orbital and spin photovoltaic effects in 2D ferroelectric materials, supported by first-principles calculations, expanding the understanding of light-induced currents beyond charge.

Findings

Discovery of pure orbital moment current with zero charge current.

Observation of spin current generated via spin-orbit coupling.

Proposal of a device to detect charge, orbital, and spin currents simultaneously.

Abstract

We elucidate light-induced orbital and spin current through nonlinear response theory, which generalizes the well-known bulk photovoltaic effect in centrosymmetric broken materials from charge to the spin and orbital degrees of freedom. We use two-dimensional nonmagnetic ferroelectric materials (such as GeS and its analogues) to illustrate this bulk orbital/spin photovoltaic effect, through first-principles calculations. These materials possess a vertical mirror symmetry and time-reversal symmetry but lack of inversion symmetry. We reveal that in addition to the conventional photocurrent that propagates parallel to the mirror plane (under linearly polarized light), the symmetric forbidden current perpendicular to the mirror actually contains electron flows, which carry angular momentum information and move oppositely. One could observe a pure orbital moment current with zero electric charge current. This hidden photo-induced orbital current leads to a pure spin current via spin-orbit coupling interactions. Therefore, a four-terminal device can be designed to detect and measure photo-induced charge, orbital, and spin currents simultaneously. All these currents couple with electric polarization $P$, hence their amplitude and direction can be manipulated through ferroelectric phase transition. Our work provides a route to generalizing nanoscale devices from their photo-induced electronics to orbitronics and spintronics.