title: Gate-Variable Mid-Infrared Optical Transitions in a (Bi1-xSbx)2Te3Topological Insulator.
abstract: We report mid-infrared spectroscopy measurements of ultrathin, electrostatically gated (Bi1-xSbx)2Te3topological insulator films in which we observe several percent modulation of transmittance and reflectance as gating shifts the Fermi level. Infrared transmittance measurements of gated films were enabled by use of an epitaxial lift-off method for large-area transfer of topological insulator films from infrared-absorbing SrTiO3growth substrates to thermal oxidized silicon substrates. We combine these optical experiments with transport measurements and angle-resolved photoemission spectroscopy to identify the observed spectral modulation as a gate-driven transfer of spectral weight between both bulk and 2D topological surface channels and interband and intraband channels. We develop a model for the complex permittivity of gated (Bi1-xSbx)2Te3and find a good match to our experimental data. These results open the path for layered topological insulator materials as a new candidate for tunable, ultrathin infrared optics and highlight the possibility of switching topological optoelectronic phenomena between bulk and spin-polarized surface regimes.
authors.affiliation: Department of Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: William S
authors.identifier: 0000-0001-5269-2967
authors.initials: WS
authors.lastname: Whitney
authors.affiliation: Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology , Pasadena, California 91125, United States.|Kavli Nanoscience Institute, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Victor W
authors.initials: VW
authors.lastname: Brar
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, The Chinese Academy of Sciences , Beijing 100190, China.
authors.forename: Yunbo
authors.initials: Y
authors.lastname: Ou
authors.affiliation: Department of Physics, University of California-San Diego , La Jolla, California 92093, United States.|Department of Physics, Columbia University , New York, New York 10027, United States.
authors.forename: Yinming
authors.initials: Y
authors.lastname: Shao
authors.affiliation: Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Artur R
authors.initials: AR
authors.lastname: Davoyan
authors.affiliation: Department of Physics, University of California-San Diego , La Jolla, California 92093, United States.|Department of Physics, Columbia University , New York, New York 10027, United States.
authors.forename: D N
authors.initials: DN
authors.lastname: Basov
authors.affiliation: State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University , Beijing 100084, China.
authors.forename: Ke
authors.initials: K
authors.lastname: He
authors.affiliation: State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University , Beijing 100084, China.
authors.forename: Qi-Kun
authors.initials: QK
authors.lastname: Xue
authors.affiliation: Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology , Pasadena, California 91125, United States.
authors.forename: Harry A
authors.identifier: 0000-0001-9435-0201
authors.initials: HA
authors.lastname: Atwater
keywords: Bismuth antimony telluride; Burstein−Moss shift; mid-infrared; optical modulator; topological insulator; tunable optical properties