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 on 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 Tc. Above 50 K we have evidence for a gapless superconductor with s-wave pairing. © 1995 The American Physical Society.