Quasiparticle dynamics and gap structure in Hg1223 investigated with   femtosecond spectroscopy
  Measurements of the temperature dependence of the quasiparticle (QP) dynamics in Hg1223 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 Dc that closes at Tc, and another temperature independent ''pseudogap'' Dp. The zero-temperature magnitudes of the two gaps are Dc/kTc = 6 +/- 0.5 and Dp/kTc = 6.4 +/- 0.5 respectively. The quasiparticle lifetime is found to exhibit a divergence as T -> Tc from below, which is attributed to the existence of a superconducting gap which closes at Tc. Above Tc 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 bi-particle recombination process. 
J.Demsar, R.Hudej, J.Karpinski, V.V.Kabanov and D.Mihailovic