Transition properties of 2D granular thin films of Bi-Sr-Ca-Cu-O

The I-V relations of granular Bi-Sr-Ca-Cu-O thin films have been investigated. It is demonstrated that the electrical properties can be classified into two groups according to their sheet resistance. Films with lower sheet resistance show superconductive transition, where the Kosterlitz-Thouless (K-T) effect with respect to the flux soliton has been observed in the resistive transition. Films with higher sheet resistance show sharp resistivity increase at low temperature; their properties are explainable based on a new K-T effect with respect to the charge soliton.