Abstract
Using the electro-optic detection method we have detected coherent phonons of Eg 1 , Eu 1 , Eg 2 , and A 1g 1 symmetry generated in a crystalline film of Bi2 Se3 by a powerful single-cycle THz pulse. Coherent excitation of Raman active modes is interpreted as a result of three-and four-phonon interactions in the anharmonic crystal lattice of Bi2 Se3 .
Highlights
As follows from the FFT spectra of three decay traces measured in succession (Fig. 1(b)) the oscillating signal contains four frequencies of 1.1, 2.05, 4.05, and 5.3 THz that correspond to optical phonon modes of
These oscillations are caused by coherent vibrations of Bi2Se3 atoms, that are induced by the pump THz pulse
Similar experiments were described in [3] and [4], where the generation of 2 g mode was interpreted as a result of vibrationally induced symmetry breaking in the bulk and sum frequency Raman scattering respectively
Summary
Spectral width of the pulses was ~ 2 THz and the central frequency ~ 1.5 THz. the IR active phonon mode Eu1 of Bi2Se3 at 67 cm-1 (2 THz) was resonantly excited. We detected anisotropic changes of the refractive index of the Bi2Se3 film induced by the electric field of the THz pulse. We registered the dependence of the corresponding ratio Ix/Iy on the delay time between pump and probe pulses.
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