Band-dependent Quasiparticle Dynamics in Single Crystals of the Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ Superconductor Revealed by Pump-Probe Spectroscopy

TL;DR

This study uses ultrafast pump-probe spectroscopy to reveal band-dependent quasiparticle relaxation dynamics in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$, showing distinct recombination processes linked to its electronic band structure.

Contribution

It provides the first detailed analysis of band-dependent quasiparticle dynamics in this superconductor using ultrafast spectroscopy, highlighting different recombination mechanisms.

Findings

Two relaxation processes observed: fast and slow components.

Fast component's decay rate increases linearly with excitation density.

Thermal quasiparticle recombination rate increases quadratically with temperature.

Abstract

We report on band-dependent quasiparticle dynamics in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$ ($T_c = 37 K$) measured using ultrafast pump-probe spectroscopy. In the superconducting state, we observe two distinct relaxation processes: a fast component whose decay rate increases linearly with excitation density and a slow component with an excitation density independent decay rate. We argue that these two components reflect the recombination of quasiparticles in the two hole bands through intraband and interband processes. We also find that the thermal recombination rate of quasiparticles increases quadratically with temperature. The temperature and excitation density dependence of the decays indicates fully gapped hole bands and nodal or very anisotropic electron bands.