Abstract
SUMMARYWe used a scanning tunnelling microscope (STM) to measure both the tunnel current, I, and the dynamic conductance, dI/dV, at 4·2 K for a number of high‐transition temperature oxide superconductors. Large spatial variations in the tunnelling characteristics are observed. At low tunnel resistances, all samples show evidence of single electron tunnelling and incremental charging. Results on BiSrCaCu2Ox show the coexistence of charging with Josephson coupling between grains within the sample. Results on both the Bi sample and a single crystal of YBa2Cu3O6·5+x reveal possible energy gap (2A) values of 17 and 20 meV, respectively. A very sharp 5 meV gap, observed in ceramic samples of YBa2Cu3O6·5+x and Y0·5Al0·05Ba2Cu3O6·5+x, may indicate the presence of a lower temperature phase in these samples.
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