Quasiparticle relaxation in a high-Tc superconductor

Recent measurements by Eesley et al. [1] of transient reflectivity in superconducting Tl2Ba2Ca2Cu30io were interpreted as evidence for order-parameter relaxation in the vicinity of Tc, which was analyzed in terms of BCS weak coupling for A(r)/A(0). In this Comment we question this interpretation based on experimental evidence that laser pulse heating can mask the effect. Eesley et al. have shown [1] that the relaxation time TS in the superconducting state increases dramatically as TC is approached; a similar increase was observed previously in YBa2Cu307 [2,3] and in Bi2Sr2Ca2Cu20io [3]. From a detailed temperature dependence at various power levels Eesley et al. inferred [1] that in the temperature range (Tc ? T)/Tc ? 0.15 the relaxation time varies as rs oc T?(T)-1 with a BCS-type ?(T)/?(0), similar to that in the usual low-temperature superconductors [4].