Specific capacitance of Nb/AlOx/Nb Josephson junctions with critical current densities in the range of 0.1–18 kA/cm2

Abstract

The specific capacitance C_s of Nb/AlO_x/Nb Josephson tunnel junction has been measured by means of the superconducting quantum interference device (SQUID) resonance technique. We have investigated the junctions with critical current densities J_c in the range of 0.1–18 kA/cm² and found that 1/C_s linearly depends on a logarithm of J_c. This suggests that the barrier thickness is moderately uniform in the junction area and increases continuously during growth. The results also show that increasing J_c reduces time constants of the junction.