Photo-galvanic effect in Bi$_{2}$Se$_{3}$ thin films with ionic liquid gating

ORAL

Abstract

A key challenge in three dimensional (3D) topological insulators (TIs) is to reveal the helical spin-polarized surface states via electrical transport measurements. A recent study [Nature Nanotech. {\bf 7}, 96 (2012)] showed that circularly polarized light can be used to generate and control photocurrents in the 3D TI Bi$_2$Se$_3$, even at photon energies that are well above the bulk band gap. Symmetry considerations suggest that this ``photo-galvanic effect'' arises purely from photo-currents induced in the surface Dirac states. To gain insights into this phenomenon, we have carried out systematic measurements of the photo-galvanic effect in electrically gated MBE-grown Bi$_2$Se$_3$ thin films of varying thickness. By using an ionic liquid as an optically transparent gate, we map out the behavior of the photo-galvanic effect as a function of Fermi energy over a temperature range 5 K $\leq T \leq$ 300 K.

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Authors

  • Yu Pan

    Department of Physics, Penn State University

  • Anthony Richardella

    Department of Physics, Pennsylvania State University, University Park, PA 16802, USA, Department of Physics, Penn State University, Dept. of Physics and Center for Nanoscale Science, Penn State University, University Park PA 16802, Penn State University

  • Joon Sue Lee

    Department of Physics, Penn State University, Dept. of Physics, Penn State University, University Park, PA 16802

  • Thomas Flanagan

    Department of Physics, Penn State University

  • Nitin Samarth

    The Pennsylvania State University, Department of Physics, Pennsylvania State University, University Park, PA 16802, USA, Department of Physics, Penn State University, Pennsylvania State University, Dept. of Physics and Center for Nanoscale Science, Penn State University, University Park PA 16802, Penn State University