Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements

Masaki Hada; Katsura Norimatsu; Sei Ichi Tanaka; Sercan Keskin; Tetsuya Tsuruta; Kyushiro Igarashi; Tadahiko Ishikawa; Yosuke Kayanuma; R J Dwayne Miller; Ken Onda; Takao Sasagawa; Shin-Ya Koshihara; Kazutaka G Nakamura

doi:10.1063/1.4955188

Bandgap modulation in photoexcited topological insulator Bi2Te3 via atomic displacements

J Chem Phys. 2016 Jul 14;145(2):024504. doi: 10.1063/1.4955188.

Affiliations

¹ Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
² Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan.
³ Department of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-8551, Japan.
⁴ The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761, Germany.
⁵ PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan.

PMID: 27421417
DOI: 10.1063/1.4955188

Abstract

The atomic and electronic dynamics in the topological insulator (TI) Bi2Te3 under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi2Te3 trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.