Helicity dependent photocurrent in electrically gated (Bi1−xSbx)2Te3 thin films. Issue 1 (December 2017)

• Record Type: Journal Article
• Authors: Pan, Yu; Wang, Qing-Ze; Yeats, Andrew; Pillsbury, Timothy; Flanagan, Thomas; Richardella, Anthony; Zhang, Haijun; Awschalom, David; Liu, Chao-Xing; Samarth, Nitin
• Is Part Of: Nature communications. Volume 8:Issue 1(2017)
• Page Start: 1
• Page End: 9
• Publication Date: 2017-12
• Subjects: Biology -- Periodicals; Physical sciences -- Periodicals; 505
• DOI: 10.1038/s41467-017-00711-4
• Languages: English
• ISSNs: 2041-1723

Abstract

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 Sbx )2 Te3 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. Control of the directional photocurrent by polarized light in topological insulators may enable topological spintronics but is not yet well understood. Here the authors demonstrate that the directional photocurrent is due to the asymmetric optical transitions between topological surface states and bulk states.