Tunneling Current-Voltage Characteristics of Bi-2212 Intrinsic Josephson Junction Stacks

Abstract

Tunneling type current-voltage (I — V) chaxactersistics have been observed in intrinsic Josephson junction stacks of Bi2Sr2CaCu2O8 single crystals. Since the nonequilibrium effect is significant in this system, the I — V curve which has an energy gap structure is oberved only for samples with a small junction area and a small number of junctions of less than 100. The tunneling properties are characterized by the following three points: (1) the energy gap suppression by the nonequilibrium superconductivity effect, (2) large subgap conductance, and (3) a small Josephson-current normal-resistance product. Since the intrinsic tunnel junctions are considered to be almost ideal, the latter two properties are quite different from those of s-wave superconductors. Based on the two-dimensional pure d-wave superconductivity, the quasiparticle I — V characteristics are calculated and compared with the experimental results. When the gap suppression due to the nonequilibrium effect is taken into account, a good agreement is obtained, indicating that the symmetry of the pair wave function in this system is likely to be d-wave like.