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

作者：Glinka Yuri D^*; Babakiray Sercan; Johnson Trent A; Holcomb Mikel B; Lederman David

来源：Journal of Applied Physics, 2015, 117(16): 165703.

DOI：10.1063/1.4919274

Transient reflectivity traces measured for nanometer-sized films (6-40 nm) of the topological insulator Bi2Se3 revealed GHz-range oscillations driven within the relaxation of hot carriers photoexcited with ultrashort (similar to 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 similar to 35 to similar 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 Bi2Se3 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 Bi2Se3.

• 出版日期2015-4-28