On the high-resistivity contacts to YBa2Cu3O7 thin films, electrical behavior in the regime of high temperatures and high-bias voltages

We prepared in-situ Au contacts on high-quality epitaxial YBa2Cu3O7 (YBCO) films. Very high specific contact resistivity values up to ∼10−2 Ω cm2 at 4.2 K were obtained on 12×5 μm2 contact areas. This resistivity value decreased by two orders of magnitude as the temperature was raised to room temperature. In the temperature range T<200 K, the contacts showed non-ohmic behavior suggesting the presence of a well-defined insulating native Y–Ba–Cu–O barrier between the two electrodes. The electrical transport in this barrier layer was analyzed in the limit of high temperatures and high voltages to follow Mott's variable-range hopping conduction mechanism with physically reasonable parameters describing the localized states in the barrier. The high-resistivity contacts were tested successfully in quasiparticles injection experiments where the critical current Ic of the YBCO microbridge could be strongly suppressed on injection of an additional current through the contact into the superconducting channel.