Nonequilibrium superconductivity probed by time-resolved far-infrared conductivity dynamics: Comparison between MgB₂ and YBa ₂Cu₃O₇

We present studies of superconducting state recovery dynamics in superconductors probed by time-resolved optical-pump terahertz-probe spectroscopy. In these experiments femtosecond optical pulses excite the superconductor out of equilibrium, while the condensate and quasiparticle dynamics are probed by measuring the associated changes in the far-infrared conductivity as a function of time delay with respect to the excitation pulse. Recent results on MgB₂ and YBa₂Cu₃O₇ are presented, with main differences and similarities between the two pointed out and discussed.