PRESSURE CONTACTS TO BI2212 WHISKERS

Eight electrical silver contacts were attached to very small and thin orthorhombic Bi2212 single-crystal whiskers by the application of pres sure in a small cell developed especially for this purpose. No heating treatment of the sample and the contacts was necessary; thus, diffusi on of the contact material into the sample was avoided. Four contacts were made to the top ab-face of the whisker, and four to the bottom ab -face, the crystallographic c-axis being along the thickness of the wh isker. This arrangement allowed electrical measurements to be made in a variety of ways. These measurements revealed that the current distri bution is not uniform through the highly anisotropic Bi2212 supercondu ctor. A contact resistance of a few ohms was seen and it changed by le ss than 30% between the superconducting transition of the whiskers and 4.2 K. This contact resistance is due to the normal surface layers of the whiskers and shows a temperature dependence similar to that of me tallic glasses. However, the contact resistance is only of the order o f 10% of the resistance of the whiskers in the normal state and stays constant at any given temperature below the superconducting transition of the whiskers which makes this pressure contact technique valuable.