Quasiparticle dynamics and gap structure in HgBa2Ca2Cu3O8+δ investigated with femtosecond spectroscopy -: art. no. 054519

Measurements of the temperature dependence of quasiparticle (QP) dynamics in Hg1Ba2Ca2Cu3O8+delta with femtosecond time-resolved optical spectroscopy are reported. From the temperature dependence of the amplitude of the photoinduced reflection, the existence of two gaps is deduced, one temperature-dependent Delta (c)(T) that closes at T-c., and another temperature-independent "pseudogap" Delta (p). The zero-temperature magnitudes of the two gaps are Delta (c)(0)/k(B)T(c) = 6+/-0.5 and Delta (p)/k(B)T(c) = 6.4+/-0.5, respectively. The quasiparticle lifetime is found to exhibit a divergence as T --> T-c from below, which is attributed to the existence of a superconducting gap that closes at T-c. Above T-c the relaxation time is longer than expected for metallic relaxation, which is attributed to the presence of the pseudogap. The QP relaxation time is found to increase significantly at low temperatures. This behavior is explained assuming that at low temperatures the relaxation of photoexcited quasiparticles is governed by a biparticle recombination process.