Optical manipulation of Rashba-split 2-Dimensional Electron Gas tracked by TR-ARPES

A new promising approach to control the electrons' spin degree of freedom in spintronic devices consists of using optical fields. Optical fields would bolster spin devices' performance, allowing for significantly faster, yet more efficient, spin-logics. To date, research has mainly focused on the optical injection of spin currents through the photogalvanic effect, and little is known about optical control of spin-gates. To explore the possibility of all-optical manipulation of the material's spin properties, we consider the Rashba effect that manifests at semiconductors' interfaces. The Rashba effect has long been a staple in this field due to its superior electrical tunability, which led to the observation of fully spin-dependent phenomena, such as the spin-Hall effect, spin-charge conversion, and spin-torque in semiconductor devices. Here we use of ultrafast optical excitation to manipulate the spin-orbit coupling strength of Rashba states. A 2-dimensional electron gas (2DEG) is engineered at the surface of the topological insulator Bi₂Se₃. We track the Rashba-induced spin splitting of the 2DEG in energy and momentum via time and angle-resolved photoemission (TR-ARPES), which allows the direct extraction of the SOC strength dynamics. We establish that light-induced photovoltage and charge carrier redistribution can offer an unprecedented route for achieving all optically-driven THz spin-logic.