Tunneling Under Pressure

We have studied the pressure dependence of the tunneling resistance of tunnel junctions between 300 nm -thick Bi films and 20 nm-thick Al films deposited at room temperature. Native Al oxide formed by oxygen glow discharge provided the tunnel barrier. Measurements were made from room temperature to below the superconducting transition temperature of the Al film. The pressure range covered was from 0 kbar to about 10 kbar. The resistance decreases in a way easily described by simple tunneling theory. In the curves we observed a pressure dependence of structure which has, in the past, been associated with the pressure dependence of the Bi band structure. We have also investigated the pressure dependence of aluminum-aluminum oxide-aluminum tunnel junctions. Measurements were from room temperature to below the superconducting transition temperature of the Al film. The pressure range covered was from 0 kbar to about 10 kbar. The superconducting energy gap of the Al film changes at a rate of about 0.01 meV/kbar. We also observed a "bump" in the conductance vs. voltage curve that disappeared at high pressure, and we explained that occurrence in terms of a dissimilarity in the two electrodes arising from the preparation conditions.