Room-temperature single-electron charging and surface polarization in tunneling spectroscopy of high-T-c superconducting thin films

Abstract

The tunneling spectroscopy of both YBa2Cu3O7-delta (YBCO) and TlBa2Ca2Cu3O9+/-delta (Tl-1223) superconducting thin films was studied using scanning tunneling microspectroscopy. The marked staircase structure in the current-voltage characteristics showed the manifestation of single-electron charging of two series-coupled mesoscopic tunnel junctions. For YBCO films, the step width across the zero-bias voltage (Delta V-0) was larger than that of other steps (Delta V-n), with Delta V(0)congruent to 1.5L Delta V-n, as the bias voltage exceeded a threshold value. Such a step-widening anomaly, however, was not seen in Tl-1223 films. Preliminary surface polarization measurements showed that the polarization is much more hysteretic for YBCO than for Tl-1223 films, suggesting that the anomalous widening of Delta V-0 may originate from the polarization-induced residual charging effect. [S0163-1829(98)09841-5].