Abstract
The dynamics of coherent optical phonons (A 1g 1 , A 1g 2 and E g 2 ) in Bi 2 Se 3 single crystal have been observed by using femtosecond time-resolved reflection measurement. The phonons with the higher frequency have the faster damping rate (decay faster). The A 1g 2 phonons show cosine-like oscillation, while the A 1g 1 and E g 2 phonons show cosine-like oscillation. The difference in the initial phase suggests that the potential energy surface may shift significantly along the A 1g 2 eigenvector and little along the A 1g 1 and E g 2 eigenvectors in the excited state.
Highlights
Bi2Se3 has attracted considerable attention in materials science because it is the well known bulk thermoelectric materials and recognized as a topological insulator [1]
The dynamics of coherent optical phonons (A1g1, A1g2 and Eg2) in Bi2Se3 single crystal have been observed by using femtosecond time-resolved reflection measurement
The difference in the initial phase suggests that the potential energy surface may shift significantly along the A1g2 eigenvector and little along the A1g1 and Eg2 eigenvectors in the excited state
Summary
Bi2Se3 has attracted considerable attention in materials science because it is the well known bulk thermoelectric materials and recognized as a topological insulator [1]. Bi2Se3 stands out due to its simple Dirac-like surface states and relatively greater band gap of ~0.3 eV. Even though its phonon properties have been studied extensively by using Raman spectroscopies [2,3], the dynamical investigations are lacking and desired. Dynamics of phonons including phonon-phonon and phonon-carrier couplings can be studied by time-domain spectroscopy. We studied the dynamics of optical phonons in a Bi2Se3 single crystal using the femtosecond time-resolved reflection measurement. Coherent optical phonon modes (A1g1, A1g2, and Eg2) have been observed at room temperature. Their decay rates per oscillations are almost the same. The coherent A1g1 and Eg2 phonons and A1g2 are sine-like and cosine-like, respectively. The initial phases suggest that the potential energy surfaces shift in direction of A1g2 eigenvector by photoexcitation
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