Femtosecond optical detection of quasiparticle dynamics in high-Tc YBa2Cu3O7−δ superconducting thin films

Abstract

Femtosecond dynamics of photogenerated quasiparticles in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ superconducting thin films shows, at T≤${\mathit{T}}_{\mathit{c}}$, two main electronic processes: (i) quasiparticle avalanche production during hot-carrier thermalization, which takes about 300 fsec; (ii) recombination of quasiparticles to form Cooper pairs, which is completed within 5 psec. In contrastr, nonsuperconducting epitaxial films such as ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_7$ and ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_6$ show regular picosecond electronic response.