Tunneling spectroscopy of the quasiparticle Andreev bound state in ion-irradiated YBa2Cu3O7-δ/Pb junctions

Effects of disorder on the in-plane density of states of YBa2Cu3O7-delta are investigated by planar tunneling spectroscopy. Low-fluence 1-MeV He+ irradiation reduces the YBa2Cu3O7-deltaTc and mean-free path without altering the junction quality. As the dirty limit is approached, the zero-bias conductance peak (ZBCP) disappears, as expected for a quasiparticle Andreev bound state. Thus, the quasiparticle scattering rate may be determined by the ZBCP magnitude. This rate is a direct measure of the pair-breaking strength and accounts for the T-c suppression.