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 I_c of the YBCO microbridge could be strongly suppressed on injection of an additional current through the contact into the superconducting channel.