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Title: Acoustic phonon dynamics in thin-films of the topological insulator Bi{sub 2}Se{sub 3}

Transient reflectivity traces measured for nanometer-sized films (6–40 nm) of the topological insulator Bi{sub 2}Se{sub 3} revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort (∼100 fs) laser pulses of 1.51 eV photon energy. These oscillations have been suggested to result from acoustic phonon dynamics, including coherent longitudinal acoustic phonons in the form of standing acoustic waves. An increase of oscillation frequency from ∼35 to ∼70 GHz with decreasing film thickness from 40 to 15 nm was attributed to the interplay between two different regimes employing traveling-acoustic-waves for films thicker than 40 nm and the film bulk acoustic wave resonator (FBAWR) modes for films thinner than 40 nm. The amplitude of oscillations decays rapidly for films below 15 nm thick when the indirect intersurface coupling in Bi{sub 2}Se{sub 3} films switches the FBAWR regime to that of the Lamb wave excitation. The frequency range of coherent longitudinal acoustic phonons is in good agreement with elastic properties of Bi{sub 2}Se{sub 3}.
Authors:
 [1] ;  [2] ; ; ; ;  [1]
  1. Department of Physics and Astronomy, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)
  2. (Ukraine)
Publication Date:
OSTI Identifier:
22402955
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 16; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BISMUTH SELENIDES; COUPLING; ELASTICITY; ELECTROMAGNETIC PULSES; EV RANGE; EXCITATION; GHZ RANGE; LASER RADIATION; OSCILLATIONS; PHONONS; PHOTONS; REFLECTIVITY; RELAXATION; RESONATORS; SOUND WAVES; THIN FILMS; TOPOLOGY; TRANSIENTS