QUASI-PARTICLE SPECTRUM IN SUPERCONDUCTING YBA2CU3O7

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