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

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.