Helicity dependent photocurrent in electrically gated (Bi1-x Sb x )2Te3 thin films

Yu Pan, Qing Ze Wang, Andrew L. Yeats, Timothy Pillsbury, Thomas C. Flanagan, Anthony Richardella, Haijun Zhang, David D. Awschalom, Chao Xing Liu, Nitin Samarth

Research output: Contribution to journalArticle

21 Scopus citations

Abstract

Circularly polarized photons are known to generate a directional helicity-dependent photocurrent in three-dimensional topological insulators at room temperature. Surprisingly, the phenomenon is readily observed at photon energies that excite electrons to states far above the spin-momentum locked Dirac cone and the underlying mechanism for the helicity-dependent photocurrent is still not understood. Here we show a comprehensive study of the helicity-dependent photocurrent in (Bi1-x Sb x )2Te3 thin films as a function of the incidence angle of the optical excitation, its wavelength and the gate-tuned chemical potential. Our observations allow us to unambiguously identify the circular photo-galvanic effect as the dominant mechanism for the helicity-dependent photocurrent. Additionally, we use an analytical model to relate the directional nature of the photocurrent to asymmetric optical transitions between the topological surface states and bulk bands. The insights we obtain are important for engineering opto-spintronic devices that rely on optical steering of spin and charge currents.

Original languageEnglish (US)
Article number1037
JournalNature communications
Volume8
Issue number1
DOIs
StatePublished - Dec 1 2017

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Physics and Astronomy(all)

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