Distinct pseudogap and superconducting state quasiparticle relaxation dynamics in near-optimally doped SmFeAsO0.8F0.2 single crystals

TL;DR

This study uses femtosecond spectroscopy to distinguish between pseudogap and superconducting quasiparticle dynamics in a near-optimally doped SmFeAsO0.8F0.2 superconductor, revealing distinct temperature-dependent and temperature-independent gaps.

Contribution

It provides the first detailed separation of pseudogap and superconducting quasiparticle relaxation dynamics in this material, highlighting their distinct properties.

Findings

Identification of a temperature-independent pseudogap of ~61 meV

Observation of a T-dependent superconducting gap below T_c

Different saturation thresholds for pseudogap and superconducting components

Abstract

We use femtosecond spectroscopy to investigate the quasiparticle relaxation and low-energy electronic structure in a near-optimally doped pnictide superconductor with T_c=49.5 K. Multiple relaxation processes are evident, with distinct superconducting state quasiparticle (QP) recombination dynamics exhibiting a T-dependent superconducting (SC) gap, and a clear "pseudogap" (PG) -like feature with an onset around 200K indicating the existence of a temperature-independent gap of magnitude \Delta_PG= 61 +- 9 meV above T_c. Both the SC and PG components show saturation as a function of fluence with distinct saturation thresholds ~0.15 \muJ/cm^2 and 1.5 \muJ/cm^2, respectively.