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Acoustic phonon dynamics in thin-films of the topological insulator Bi2Se3.

Acoustic phonon dynamics in thin-films of the topological insulator Bi2Se3.

Authors :
Glinka, Yuri D.
Babakiray, Sercan
Johnson, Trent A.
Holcomb, Mikel B.
Lederman, David
Source :
Journal of Applied Physics; 2015, Vol. 117 Issue 16, p165703-1-165703-5, 5p, 4 Graphs
Publication Year :
2015

Abstract

Transient reflectivity traces measured for nanometer-sized films (6-40 nm) of the topological insulator Bi<subscript>2</subscript>Se<subscript>3</subscript> 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<subscript>2</subscript>Se<subscript>3</subscript> 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<subscript>2</subscript>Se<subscript>3</subscript>. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
00218979
Volume :
117
Issue :
16
Database :
Complementary Index
Journal :
Journal of Applied Physics
Publication Type :
Academic Journal
Accession number :
102388392
Full Text :
https://doi.org/10.1063/1.4919274