title: Gigantic surface lifetime of an intrinsic topological insulator.
abstract: The interaction between light and novel two-dimensional electronic states holds promise to realize new fundamental physics and optical devices. Here, we use pump-probe photoemission spectroscopy to study the optically excited Dirac surface states in the bulk-insulating topological insulator Bi_{2}Te_{2}Se and reveal optical properties that are in sharp contrast to those of bulk-metallic topological insulators. We observe a gigantic optical lifetime exceeding 4  μs (1  μs=10^{-6}  s) for the surface states in Bi_{2}Te_{2}Se, whereas the lifetime in most topological insulators, such as Bi_{2}Se_{3}, has been limited to a few picoseconds (1  ps=10^{-12}  s). Moreover, we discover a surface photovoltage, a shift of the chemical potential of the Dirac surface states, as large as 100 mV. Our results demonstrate a rare platform to study charge excitation and relaxation in energy and momentum space in a two-dimensional system.
authors.affiliation: Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.|Condensed Matter and Magnet Science Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Madhab
authors.initials: M
authors.lastname: Neupane
authors.affiliation: Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Su-Yang
authors.initials: SY
authors.lastname: Xu
authors.affiliation: ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yukiaki
authors.initials: Y
authors.lastname: Ishida
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.|International Center for Quantum Materials, Peking University, Beijing 100871, China.
authors.forename: Shuang
authors.initials: S
authors.lastname: Jia
authors.affiliation: Department of Physics, University of California, Berkeley, California 94720, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Fregoso
authors.affiliation: Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.affiliation: Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Ilya
authors.initials: I
authors.lastname: Belopolski
authors.affiliation: Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Guang
authors.initials: G
authors.lastname: Bian
authors.affiliation: Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Nasser
authors.initials: N
authors.lastname: Alidoust
authors.affiliation: Condensed Matter and Magnet Science Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Durakiewicz
authors.affiliation: Department of Physics, Joint Quantum Institute and Condensed Matter Theory Center, University of Maryland, College Park, Maryland 20742-4111, USA.|School of Physics, Monash University, Melbourne, Victoria 3800, Australia.
authors.forename: Victor
authors.initials: V
authors.lastname: Galitski
authors.affiliation: ISSP, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Shik
authors.initials: S
authors.lastname: Shin
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Cava
authors.affiliation: Joseph Henry Laboratory and Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.|Princeton Center for Complex Materials, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: M Zahid
authors.initials: MZ
authors.lastname: Hasan