Intermediate vortex states in nanoscale anti-dots and mesoscopic superconductors

Abstract

We have fabricated anti-dots array in Nb and NbN, and high-Tc superconductor Bi2Sr2CaCu2Oy (Bi-2212), and have measured the flow-resistance of vortices perpendicular to the array and magnetic field. We could produce a variety of vortex-matching effect; the usual and the fractional matching. In low-Tc superconductors, the usual matching effect shows "dips" in the flow resistance at the matching field. However, it shows "humps" at higher matching magnetic fields to be related to the formation of giant vortices and/or interstitial vortices. In Bi-2212, the matching effect is closely related to the first order transition of vortex lattice melting in the pristine samples in the presence of the anti-dot arrays. We also have measured the vortex state in mesoscopic type-I superconductor of In. This includes the observation of topological hysteresis with a signature of occurrence in different critical fields during vortex entry and exit. We will show the existence of a metastable configuration of vortices depending on the recipes to access them, and demonstrate the manifestation of superheating and supercooling of superconducting and normal states, respectively, across the superconducting transition.