Effect of Rashba splitting on ultrafast carrier dynamics in BiTeI

Narrow-gap semiconductors with strong spin-orbit coupling such as bismuth tellurohalides have become popular candidates for spintronic applications. But driving spin-polarized photocurrents in these materials with circularly polarized light requires picosecond lifetimes of the photoexcited carriers and low spin-flip scattering rates. In search of these essential ingredients, we conducted an extensive study of the carrier dynamics on the Te-terminated surface of BiTeI, which exhibits a giant Rashba splitting of both surface and bulk states. We observe a complex interplay of surface and bulk dynamics after photoexcitation. Carriers are rapidly rearranged in momentum space by quasielastic phonon and defect scattering, while a phonon bottleneck leads to a slow equilibration between bulk electrons and lattice. The particular band dispersion opens an inelastic decay channel for hot carriers in the form of plasmon excitations, which are immanent to Rashba-split systems. These ultrafast scattering processes effectively redistribute excited carriers in momentum and energy space and thereby inhibit spin-polarized photocurrents.This project was supported by the German Research Foundation via the Collaborative Research Center TRR 227 on Ultrafast Spin Dynamics, project A1, and the German-Russian Interdisciplinary Science Center (GRISC). A.S.K. is indebted to the International Max Planck Research School Functional Interfaces in Physics and Chemistry for financial support. B.A. and V.V. acknowledge travel support by GRISC. O.E.T. and K.A.K. were supported by the Russian Science Foundation (Project No. 17-12-01047) and a state contract of ISP and IGM SB RAS. A.S. acknowledges support by Russian Science Foundation (Grant No. 18-12-00062). A.S. and E.V.C. acknowledge support by the Saint Petersburg State University (Grant No. ID 73028629).Peer reviewe