Studies were made of the photo-excited quasiparticle dynamics in MgB2 where, using fs optical techniques, Cooper pair-breaking dynamics were temporally resolved for the first time. The Cooper pair-breaking dynamics were strongly temperature and photo-excitation intensity dependent. Analysis of the Cooper pair-breaking dynamics using the Rothwarf-Taylor equations suggests that the anomalous Cooper pair-breaking dynamics arises from the fact that in MgB2 photo-excitation was 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 were determined.

Pair-Breaking and Superconducting State Recovery Dynamics in MgB2. J.Demsar, R.D.Averitt, A.J.Taylor, V.V.Kabanov, W.N.Kang, H.J.Kim, E.M.Choi, S.I.Lee: Physical Review Letters, 2003, 91[26], 267002 (3pp)