Comment on ``Quasiparticle Decay Effects in the Superconducting Density of States Evidence.pdf

Comment on “Quasiparticle Decay Effects in the Superconducting Density of States: Evidence for d-Wave Pairing in the Cuprates” 5 9 9 1 l u J 8 1 1 Georgios VARELOGIANNIS v 3 7 Dipartimento di Fisica 0 7 0 Universit`a degli studi di Roma ”La Sapienza” 5 9 Ple. A.Moro 2, 00185 Roma, Italy / t a m - d n o c : v i X r a 1 In a recent letter [1], D.Coffey and L.Coffey analyzed some characteristic anomalous structures in tunneling and photoemission spectra of cuprates. They concluded that the dip-like structure which appears above the gap might be considered as evidence for d-wave pairing. In the analysis of [1], this structure is due to “deviations from weak coupling mean-field behavior of the superconductivity in those materials”. While we perfectly agree with this statement, we disagree with the analysis and conclusions of [1] as well with the supposed origin of the deviations from mean-field behavior. When quasiparticle lifetime effects become important, for the descritption of supercon- ductivity it is necessary to consider a retarded strong coupling approach. The necessity of a strong coupling approach is valid even if the symmetry of the pairing is d-wave [2]. The errors in the analysis and conclusions of [1] are due to the use of a non-retarded framework, which should exclude quantitative comparison with experiment. In the case of d-wave pairing for example, the use of a retarded formalism led to the reduction of the critical temperature by an order of magnitude [2] compared to that obtained by a non-retarded approach. The arguments advanced in [1] related with a system