4 CONTACT ELECTRICAL MEASUREMENTS ON THE ANISOTROPIC HIGH-T-C SUPERCONDUCTORS - VOLTAGE REVERSALS

We describe three mechanisms for the anomalous voltage reversals which are occasionally observed during four contact current-voltage measure ments on the high temperature superconductors. Voltage reversals have been frequently observed for whiskers of the bismuth strontium calcium copper oxide (BSSCO) compounds, and we describe measurements made on high quality whiskers of the 2:2:1:2 and 2:2:2:3 phases. A simple mode l based on extreme anisotropy plus offset contacts can explain the gro ss features of four contact measurements in the ohmic flux-flow regime , but not the wealth of reversal phenomena found for the IVVI configur ation in the lower temperature irreversibility region.