Quasiparticle Dynamics in FeSe Superconductors Studied by Femtosecond Spectroscopy

Abstract

The ultrafast quasiparticle dynamics in FeSe single crystals were measured by using dual-color transient reflectivity measurements (Delta R/R) from 4.4 to 290 K. In general, the typical Delta R/R of FeSe includes two significant components. One is the relaxation of photoinduced quasiparticles, which has been used to estimate the electron-phonon coupling strength (lambda=0.16). The other is the oscillation component due to the acoustic phonon. Moreover, the acoustic phonon's energy estimated from the period of oscillation in Delta R/R markedly shrinks around 90 K, which is the so-called phonon softening.