Optical manipulation of Rashba-split 2-Dimensional Electron Gas

TL;DR

This paper demonstrates that ultrafast optical excitation can manipulate the Rashba spin splitting in a 2D electron gas at a topological insulator surface, enabling potential all-optical THz spin logic devices.

Contribution

It provides the first direct evidence of optical control over Rashba spin splitting using TR-ARPES on a topological insulator surface.

Findings

Optical excitation modulates Rashba spin splitting on sub-picosecond timescales.

Light-induced photovoltage and charge redistribution alter spin-orbit coupling.

Potential for developing all-optical THz spin logic devices.

Abstract

In spintronic devices, the two main approaches to actively control the electrons' spin degree of freedom involve either static magnetic or electric fields. An alternative avenue relies on the application of optical fields to generate spin currents, which promises to bolster spin-device performance allowing for significantly faster and more efficient spin logic. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about the direct optical control of the intrinsic spin splitting. Here, to explore the all-optical manipulation of a material's spin properties, we consider the Rashba effect at a semiconductor interface. The Rashba effect has long been a staple in the field of spintronics owing to its superior tunability, which allows the observation of fully spin-dependent phenomena, such as the spin-Hall effect, spin-charge conversion, and spin-torque in semiconductor devices. In this work, by means of time and angle-resolved photoemission spectroscopy (TR-ARPES), we demonstrate that an ultrafast optical excitation can be used to manipulate the Rashba-induced spin splitting of a two-dimensional electron gas (2DEG) engineered at the surface of the topological insulator Bi$_{2}$Se$_{3}$. We establish that light-induced photovoltage and charge carrier redistribution -- which in concert modulate the spin-orbit coupling strength on a sub-picosecond timescale -- can offer an unprecedented platform for achieving all optically-driven THz spin logic devices.