Band resolved imaging of photocurrent in a topological insulator

Soifer H, Gauthier A, Kemper AF, Rotundu CR, Yang S, Xiong H, Lu DH, Hashimoto M, Kirchmann PS, Sobota JA, Shen ZX
Phys. Rev. Lett. 122, 167401 (2019)


We study the microscopic ingredients to photocurrent generation in the topological insulator Bi2Se3 using time-resolved photoemission spectroscopy. We image the unoccupied band structure as it evolves following an optical excitation and observe an asymmetric electron population in momentum space that is controlled by the light polarization. By analyzing the rise times of the population we identify which occupied and unoccupied electronic states are coupled by optical excitation. We conclude that photocurrents can only be excited via resonant optical transitions coupling to spin-orbital textured states. Our work provides a microscopic understanding of how to control photocurrents in materials with spin-orbit coupling and broken inversion symmetry.