Quantification of electron–phonon interaction in bismuth telluride under hydrostatic pressure via ultrafast spectroscopy

Here, we demonstrate a strategy for the quantification of electron–phonon interaction (EPI) of bismuth telluride (Bi2Te3) under hydrostatic pressure through systematic femtosecond pump-probe spectroscopy. Two optical phonon modes, namely A1g and Eg with frequencies of 1.87 and 3.71 THz at ambient pressure, are detected using time-resolved transient reflection (TR) measurement. Frequencies of both coherent phonon oscillations increase monotonically by around 33% and 17%, respectively, with the rising pressure up to 5.67 GPa, indicating pressure-induced phonon-hardening effect. The mode-specific electron–phonon coupling constant λ of Bi2Te3 under different pressures are calculated with the frequency of the A1g mode. It turns out that the variation of phonon lifetime and the corresponding phonon dephasing rate of the A1g mode may result from the pressure modification of λ. Our findings reveal the significant role of EPI in phonon transport and shed light on further manipulation on thermoelectric efficiency of Bi2Te3 with external strain.