Quasiparticle spectrum in superconducting YBa2Cu3O7

We have used the real-axis Eliashberg equations for an anisotropic superconductor to study the quasiparticle density of states of superconducting YBa2Cu3O7 in a temperature range from 0 up to 120 K. A first-principles electronic structure and a nonorthogonal tight-binding method was used to calculate the electron-phonon interaction. The large variation we found in gap energies for different bands and directions an the Fermi surface and strong frequency dependence of the gap explains broad features seen in the low temperature tunneling density of states as well as structure seen close to T-c. Above 50 K we have evidence for a gapless superconductor with s-wave pairing.