Time-resolved dynamics of the superconducting two-gap state in MgB2 thin films

TL;DR

This study uses femtosecond pump-probe techniques to investigate the ultrafast carrier dynamics in MgB2 thin films, revealing distinct electron-phonon relaxation processes and the temperature-dependent behavior of two superconducting gaps.

Contribution

It provides the first detailed time-resolved analysis of the two-gap superconducting state in MgB2, highlighting the different relaxation processes associated with each gap.

Findings

Electron-phonon relaxation occurs at sub-ps and few-ps timescales.

Superconducting relaxation time diverges at two different Tc's.

Superconducting gap amplitudes follow two distinct temperature dependences.

Abstract

Femtosecond pump-probe studies show that carrier dynamics in MgB2 films is governed by the sub-ps electron-phonon (e-ph) relaxation present at all temperatures, the few-ps e-ph process well pronounced below 70 K, and the sub-ns superconducting relaxation below Tc. The amplitude of the superconducting component versus temperature follows the superposition of the isotropic dirty gap and the 3-dimensional gap dependences, closing at two different Tc values. The time constant of the few-ps relaxation exhibits a double-divergence at temperatures corresponding to the Tc's of the two gaps.