Laser-induced charge and spin photocurrents at BiAg$_2$ surface: a first principles benchmark

TL;DR

This study uses first-principles calculations to analyze laser-induced charge and spin photocurrents at the BiAg₂ surface, providing a benchmark for understanding Rashba surface phenomena relevant to ultrafast spintronics.

Contribution

It offers a comprehensive first-principles benchmark of laser-induced photocurrents at Rashba surfaces, including symmetry analysis and the role of electronic transitions.

Findings

Large in-plane photocurrents confirmed at BiAg₂ surface.

Photocurrent symmetry aligns with light helicity and magnetization.

Resonant electronic transitions significantly influence photocurrent magnitude.

Abstract

Here, we report first principles calculations and analysis of laser-induced photocurrents at the surface of a prototype Rashba system. By referring to Keldysh non-equilibrium formalism combined with the Wannier interpolation scheme we perform first-principles electronic structure calculations of a prototype BiAg$_2$ surface alloy, which is a well-known material realization of the Rashba model. In addition to non-magnetic ground state situation we also study the case of in-plane magnetized BiAg$_2$. We calculate the laser-induced charge photocurrents for the ferromagnetic case and the laser-induced spin photocurrents for both the non-magnetic and the ferromagnetic cases. Our results confirm the emergence of very large in-plane photocurrents as predicted by the Rashba model. The resulting photocurrents satisfy all the symmetry restrictions with respect to the light helicity and the magnetization direction. We provide microscopic insights into the symmetry and magnitude of the computed currents based on the ab-initio multi-band electronic structure of the system, and scrutinize the importance of resonant two-band and three-band transitions for driven currents, thereby establishing a benchmark picture of photocurrents at Rashba-like surfaces and interfaces. Our work contributes to the study of the role of the interfacial Rashba spin-orbit interaction as a mechanism for the generation of in-plane photocurrents, which are of great interest in the field of ultrafast and terahertz spintronics.