Pair-breaking and superconducting state recovery dynamics in MgB2

TL;DR

This study uses femtosecond optical techniques to temporally resolve Cooper pair breaking and quasiparticle dynamics in MgB2, revealing temperature and intensity dependencies and the role of phonons in energy relaxation.

Contribution

First direct measurement of photoexcited quasiparticle dynamics in MgB2, highlighting the role of high-frequency phonons in pair-breaking and energy relaxation processes.

Findings

Cooper pair breaking dynamics are temperature and intensity dependent.

Energy relaxation initially involves high-frequency phonons, not electron-electron thermalization.

Quantified quasiparticle recombination rate and pair-breaking probability by phonons.

Abstract

We present studies of the photoexcited quasiparticle dynamics in MgB2 where, using femtosecond optical techniques, Cooper pair breaking dynamics (PBD) have been temporally resolved for the first time. The PBD are strongly temperature and photoexcitation intensity dependent. Analysis of the PBD using the Rothwarf-Taylor equations suggests that the anomalous PBD arises from the fact that in MgB2 photoexcitation is initially followed by energy relaxation to high frequency phonons instead of, as commonly assumed, e-e thermalization. Furthermore, the bare quasiparticle recombination rate and the probability for pair-breaking by phonons have been determined.