Subgap structures in intrinsic Josephson junctions of Tl2Ba2Ca2Cu3O10+delta and Bi2Sr2CaCu2O8+delta

We report on pronounced structures in the current-voltage characteristics of intrinsic Josephson junctions in the high-T-c superconductors Tl2Ba2Ca2Cu3O10+delta and Bi2Sr2CaCu2O8+delta. The structures appear well below the superconducting gap, independent of sample geometry, magnetic field, and temperature up to 0.5T(c). We discuss possible explanations and show that the structures could be explained by a single peak in the quasiparticle current, possibly arising from a subgap structure in the quasiparticle density of states. For superconducting superlattices a subgap peak has been predicted and could explain our results.