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 ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{10+\ensuremath{\delta}}$ and ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$. 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.