title: Manifestation of a Second Dirac Surface State and Bulk Bands in THz Radiation from Topological Insulators.
abstract: Topological insulators (TIs) are interesting quantum matters that have a narrow bandgap for bulk and a Dirac-cone-like conducting surface state (SS). The recent discovered second Dirac surface state (SS) and bulk bands (BBs) located ~1.5 eV above the first SS are important for optical coupling in TIs. Here, we report on the time-domain measurements of THz radiation generated from TIs n-type Cu(0.02)Bi2Se3 and p-type Bi2Te3 single crystals by ultrafast optical pulse excitation. The observed polarity-reversal of the THz pulse originated from transient current is unusual, and cannot be reconciled with the photo-Dember effect. The second SS and BBs are found to be indispensable for the explanation of the unusual phenomenon. Thanks to the existence of the second SS and BBs, TIs manifest an effective wide band gap in THz generation. The present study demonstrates that time-domain THz spectroscopy provide rich information of the optical coupling and the electronic structure of TIs.
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Chien-Ming
authors.initials: CM
authors.lastname: Tu
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Tien-Tien
authors.initials: TT
authors.lastname: Yeh
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Wen-Yen
authors.initials: WY
authors.lastname: Tzeng
authors.affiliation: Department of Electrical and Computer Engineering, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Yi-Ru
authors.initials: YR
authors.lastname: Chen
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Hsueh-Ju
authors.initials: HJ
authors.lastname: Chen
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Shin-An
authors.initials: SA
authors.lastname: Ku
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.|Taiwan Consortium of Emergent Crystalline Materials, Ministry of Science and Technology, Taipei 10601, Taiwan, R.O.C.
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Luo
authors.affiliation: Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Jiunn-Yuan
authors.initials: JY
authors.lastname: Lin
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Kaung-Hsiung
authors.initials: KH
authors.lastname: Wu
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Jenh-Yih
authors.initials: JY
authors.lastname: Juang
authors.affiliation: Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan 300, R.O.C.|Advanced Ultrafast Laser Research Center and Department of Engineering Science, The University of Electro-Communications, Chofugaoka 1-5-1, Chofu, Tokyo 182-8585, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Cheng-Maw
authors.initials: CM
authors.lastname: Cheng
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu, Taiwan 300, R.O.C.
authors.forename: Ku-Ding
authors.initials: KD
authors.lastname: Tsuei
authors.affiliation: Institut de Physique des Nanostructures, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
authors.forename: Helmuth
authors.initials: H
authors.lastname: Berger
authors.affiliation: Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan, R.O.C.
authors.forename: Raman
authors.initials: R
authors.lastname: Sankar
authors.affiliation: Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan, R.O.C.
authors.forename: Fang-Cheng
authors.initials: FC
authors.lastname: Chou