Superconducting contacts on YBa2Cu3O7−x in magnetic fields

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Abstract
The contact resistance Rc of pressed and diffused gold contacts on polycrystalline YBa2Cu3O7−x is known to vanish below the critical temperature Tc≊90 K. The lack of a voltage drop over the contacts at finite currents strongly suggests pair tunneling between the high Tc superconductor and the adjacent gold layer, becoming superconducting via the proximity effect. Comparison of the current‐voltage characteristics with those calculated including a Josephson current reveals a point contact structure rather than a homogeneous contact area. The contacts are studied at high currents up to I=19 A at different temperatures and magnetic fields. Staying superconducting at externally applied magnetic fields B up to B=30 mT, Rc rises monotonically with increasing magnetic field to Rc=180 μΩ at B=100 mT. This very low contact resistance persists essentially up to B=10 T, opening the possibility to design high magnetic field devices with negligible contact power dissipation.