Pair-breaking and superconducting state recovery dynamics in [formula presented]

We present studies of the photoexcited quasiparticle dynamics in [Formula presented] 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 [Formula presented] photoexcitation is initially followed by energy relaxation to high frequency phonons instead of, as commonly assumed, [Formula presented] thermalization. Furthermore, the bare quasiparticle recombination rate and the probability for pair breaking by phonons have been determined.