No abstract

No abstract

Coffey and Coffey Reply: Varelogiannis [1] has missed the point of our calculation [2] which was motivated by the data of Zasadzinski et al. [3]. In these data there is a feature which scales with D 0 at values of the bias across a junction given by eV 3D 0 in the tunneling conductance of superconductor-insulator-superconductor junctions as well as the peak at eV 2D 0 expected from the mean-field approximation. This scaling holds for superconductors whose T c 's vary by a factor of 20. The scaling clearly points to something intrinsic to the superconducting state and is absent from the meanfield approximation for superconductivity. These data are shown in Refs. [3,4]. Given this scaling, Varelogiannis' point about the precision with which D 0 is known is irrelevant.Our calculation is aimed at bringing out the effect of going beyond the mean-field approximation. One consequence of these corrections is that the mean-field quasiparticle eigenstates spontaneously decay because they are not eigenstates of the full Hamiltonian but only of the BCS reduced Hamiltonian. This phenomenon occurs independently of the details of the effective interaction responsible for the superconductivity. The strong-coupling effects in phonon mediated superconductors reflect the frequency dependence of the self-energy coming from the frequency dependence of the phonon density of states. One could imagine doing the same calculation with magnons. However, it is very unlikely that there happens to be a sharp feature giving very large strong-coupling effects at precisely 3D 0 in a set of superconductors whose D 0 's vary by more than an order of magnitude but which share the same basic component, copper oxygen planes. Furthermore, the strong-coupling features have been investigated for some of the cuprates, and they turn out to be very small, ϳ1%, just as is the case in most superconductors [3,5]. On the other hand, the dip feature is close to a 10% effect.After the original submission, Varelogiannis introduced a second issue in a new version of his Comment, namely, that our simple model gives a dip in the direction in momentum space in which the gap goes to zero. He points out that this is in contradiction to Dessau et al. data [6]. If he had read Ref.[4] of our original reply, we would have found that the direction along which the dip feature is seen depends on the choice of band structure. One of us showed [4] that by putting a next-nearest neighbor hopping term into the nearest neighbor tightbinding band structure the anisotropy could be made to vanish. The fact that a simple band structure does not reproduce all the details of these materials does not invalidate our identification of the dip feature in the tunneling conductance. This result has been published for nearly two years now. We note that this contribution to the quasiparticle self-energy is present in both the k

Evidence for the validity of the pairing glue interpretation of high temperature superconductivity is presented using a modified Eliashberg analysis of experimental superconductor-insulator-superconductor (SIS) tunneling data in B 2 Sr 2 CaCu 2 O 8 (Bi2212) over a wide range of doping. This is accomplished by extracting detailed information on the diagonal and anomalous contributions to the quasiparticle selfenergy. In particular, a comparison of the imaginary part of the anomalous self-energy ImÈð!Þ and the pairing glue spectral function 2 Fð!Þ used in the model is consistent with Hubbard model simulations in the literature. In addition, the real part of the diagonal self-energy for optimal doped Bi2212 bears a strong resemblance to that obtained from photoemission experiments.

No abstract