Femtosecond Optical Detection of Quasiparticle Dynamics in Single-Crystal Bi₂Sr₂CaCu₂O_8+δ

Quasiparticle dynamics of an optimally doped Bi₂Sr₂CaCu₂O_8+δ single crystal is investigated by the femtosecond pump--probe technique. Temperature
dependences of amplitude of the photoinduced differential reflectivity and the relaxation time show the evidence of strong phonon bottleneck. The experimental results are analysed by the Rothwarf--Taylor model.