Laser-induced charge and spin photocurrents at the BiAg_{2} surface: A first-principles benchmark

Abstract

Here, we report first-principles calculations of laser-induced photocurrents at the surface of a prototype Rashba system. By referring to Keldysh nonequilibrium 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 the nonmagnetic 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 nonmagnetic and the ferromagnetic cases. Our results confirm the emergence of very large in-plane photocurrents as predicted by the Rashba model and are in agreement with previous experimental measurements of THz emission generated at Bi/Ag interfaces. 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 multiband 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 establishing the interfacial Rashba spin-orbit interaction as a major mechanism for the generation of in-plane photocurrents, which are of great interest in the field of ultrafast and terahertz spintronics.