Energy gaps in Bi-Sr-Ca-Cu-O and Bi-Sr-Cu-O systems by electron tunneling

We report the results of electron tunneling studies of the Bi-Sr-Ca-Cu-O and Bi-Sr-Cu-O systems by using point-contact tunneling. In these studies, we observed two distinctive energy gaps at each Bi-Sr-Ca-Cu-O system, having extremely large values. The larger values of the ratios 2/kTc are 1012 for Bi2Sr2CaCu2Oy and 911 for Bi2Sr2Ca2Cu3Oiy and the smaller values are 5.56.1 for Bi2Sr2Ca2Cu3Oy. These differences can be attributed to the gap anisotropies and the ratios of gaps are 1.71.8 for Bi2Sr2CaCu2Oy and 1.51.8 for Bi2Sr2Ca2C3Oy. The ratio 2/kTc in the Ca-absent material Bi2Sr2CuOy was obtained as 5.47.4. The gap values are quite reproducible for the bulk, single crystal, and thin films.