Nonequilibrium superconductivity in Y1-xPrxBa2Cu3O7 thin films
  We have measured the picosecond conductivity dynamics in Y1-xPrxBa2Cu3O7 thin films from 0.3-2.0 terahertz. Our experimental technique measures the complex conductivity $\sigma_{re}(\omega$) + i$\sigma_{im}(\omega$) permitting the simultaneous observation of superconducting pair and quasiparticle dynamics. We emphasize aspects of the conductivity dynamics which extend our previous results. In particular, the recovery of $\sigma_{re}$ is faster than $\sigma_{im}$, and the recovery of $\sigma_{im}$ decreases with increasing frequency. This suggests another carrier relaxation pathway, in addition to superconducting pair recovery, following optical excitation. 
R.D. Averitt, V. K. Thorsmolle, Q.X. Jia, S. A. Trugman, A. J. Taylor