Planar tunneling spectroscopy of Y1-xPrxBa2Cu3O7 thin films as a function of crystallographic orientation

We present a systematic study of the charge transport and quasiparticle tunneling properties of Y1-xPrxBa2Cu3O7 thin films. Pr doping increases the resistivity along the copper oxide planes and suppresses the superconducting critical temperature T-c. ultimately inducing a superconductor-insulator transition. The tunneling conductance is reproducible and correlated with the crystallographic film orientation. The crystallographic dependence can be divided into two distinct categories: tunneling into (001)-oriented (c-axis) films and tunneling into (100)-, (110)-, and (103)-oriented (ab-oriented) films, c-axis tunneling data exhibit a conductance dip at zero bias and a broad temperature-dependent peak over similar to 15-40 mV that decreases in magnitude but stays fixed in energy for increasing Pr doping levels. ab-plane tunneling data exhibit a zero-bias conductance peak and a gaplike feature at an energy that scales roughly linearly with T-c for x = 0.0, 0.2, and 0.4. When x = 0.5, the resistivity is not linear in temperature and a zero-bias conductance dip is observed. The background conductance that ensures conservation of states in the low-temperature nb-plane data exhibits temperature- and doping-dependent structure over - 15-40 mV that is very similar to the peak observed in c-axis tunneling. Finally, analysis of the temperature and magnetic field dependence of the zero bias conductance peak indicates that states are conserved to within similar to 20%, supporting its interpretation as a feature of a superconducting density of states.