Dynamics of cooper pair formation in Bi2Sr2CaCu2O8+δ -: art. no. 060510

We report ultrafast measurements of the transient terahertz conductivity in the high-T-C superconductor Bi2Sr2CaCu2O8+delta. After depletion of the superconducting condensate by optical excitation, the ensuing dynamics is tracked with high sensitivity at various excitation densities and temperatures. We measure low-energy spectra and shapes of decay that demonstrate a bimolecular kinetics of condensate formation on a picosecond time scale and yield a measure of quasiparticle interactions hidden in linear spectroscopy.