The nature of spin transport in the bulk and side surface of three-dimensional topological insulator thin film geometry is a relatively unexplored subject, compared to the extensively studied top and bottom surface states. Here we employ time- and space-resolved helicity-dependent photocurrent measurements to investigate the effect of optically excited bulk carriers on the spin-polarized topological side surface conduction. Time-resolved femtosecond double-pulse excitation reveals that the spin current toward the side surface arises from the bulk-originated spin Hall effect (SHE), whose microscopic origin is governed by an Elliott-Yafet-type spin relaxation mechanism via an extrinsic side jump process. Bias- and temperature-dependent measurements further confirm that the spin scattering in Bi2Se3 has multiple sources including impurity and electron-phonon scattering. The SHE-assisted side surface spin conduction shows an exceptionally high charge-to-spin conversion efficiency of 35% at 77 K, which may offer new spintronic applications of topological insulators such as spin-orbit torque or spin-flip controlled light-emitting devices.
Bibliographical noteFunding Information:
J.L., S.S., S.P., S.C., S.L, C.I., S.C., and H.C. were supported by the National Research Foundation of Korea (NRF) through the government of Korea (MSIP) (grant nos. NRF-2016R1A4A1012929 and NRF-2015R1A2A1A10052520) and the Global Frontier Program (grant no. 2014M3A6B3063709). H.K. and J.S.K. were supported by SRC Center for Topological Matter (grant no. 2011-0030785) and Max-Plank POSTECH/ KOREA Research Initiative (grant no. 2016K1A4A4A01922028). J.K. and D.L. were supported by the Basic Science Research Program through the NRF funded by MSIP (grant no. NRF-2015R1C1A1A02037430).
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Atomic and Molecular Physics, and Optics
- Electrical and Electronic Engineering