Investigation of phonon-mediated relaxation within the topological insulator Bismuth Tellurium

In this work, using double pulses excitation technique, the energy coupling ratio from excitaton laser to coherent phonons of topological insulator bismuth tellurium(Bi2Te3) thin film was characterized. First of all, by analyzing excitation intensity dependent heating temperature of the thin film from the transmission pump probe results, the coherent phonon generation and the energy coupling from laser to phonons were confirmed. The coupling ratio was accordingly estimated and with decreasing nature as increasing temporal spacing between double pulses. Furthermore, the frequency and intensity of the phonon mode were investigated as well. Beside identification of the relaxation characteristic, we also find evidence of phonon-mediated relaxation of the energy density at the Bi2Te3 surface.