Quasiparticle dynamics and phonon softening in FeSe superconductors

TL;DR

This study uses dual-color transient reflectivity to explore quasiparticle dynamics and phonon behavior in FeSe superconductors, revealing phase transitions, phonon softening, and an unconventional superconducting mechanism.

Contribution

It provides new insights into the phase transitions, phonon softening, and electron-phonon coupling in FeSe, highlighting an unconventional superconductivity origin.

Findings

Anomalous changes at 90 K and 230 K indicating phase transitions.

Phonon softening associated with structural transition.

Electron-phonon coupling constant {1} = 0.16 supporting unconventional superconductivity.

Abstract

Quasiparticle dynamics of FeSe single crystals revealed by dual-color transient reflectivity measurements ({\Delta}R/R) provides unprecedented information on Fe-based superconductors. The amplitude of fast component in {\Delta}R/R clearly tells a competing scenario between spin fluctuations and superconductivity. Together with the transport measurements, the relaxation time analysis further exhibits anomalous changes at 90 K and 230 K. The former manifests a structure phase transition as well as the associated phonon softening. The latter suggests a previously overlooked phase transition or crossover in FeSe. The electron-phonon coupling constant {\lambda} is found to be 0.16, identical to the value of theoretical calculations. Such a small {\lambda} demonstrates an unconventional origin of superconductivity in FeSe.