Magneto-transport properties of thin superconducting strips in the framework of Time Dependent Ginzburg Landau model

Abstract

This dissertation is addressed to summarize my experimental/phenomenological research activities conducted at the laboratories of Physics Department, University of Salerno. The experimental work consisted in the fabrication of mesoscopic superconducting devices made using Electron Beam Lithography (EBL) on Niobium thin films obtained by magnetron RF sputtering deposition. Among the devices fabricated with success are worthy of attention thin strips (25 nm) of Niobium with a regular array of antidots in deep submicron scale (15 nm diameter holes spaced 50 nm) on which studies were performed about the matching of Abrikosov vortices lattice at high magnetic fields. Other devices successfully produced have been superconducting strips with lateral dimensions of the order of microns, but with variable thickness on the nanometer scale. On this type of devices we have conducted a study of magneto‐transport properties at cryogenic (liquid helium) and deep cryogenic (300 mK) temperatures in a magnetic field both parallel and perpendicular to the substrate. The most interesting result was that these devices may exhibit a behavior of superconducting diode. In parallel to experimental activities were carried out investigations aimed at the theoretical and computational description/interpretation of the phenomena observed experimentally in the framework of Time‐Dependent Ginzburg‐Landau (TDGL) model of superconductivity. The direct numerical integration of the TDGL as well as its specialization to magneto‐transport properties of superconducting strips in finite and unconventional geometry had not tradition at the Department of Physics, and we gave an original contribution to this research line. Results acquired in this activity that are worth mentioning are the interpretation of the asymmetry and bistability in a Abrikosov diode based on superconductor/ferromagnet strips, the interpretation of matching properties in strips with square arrays of antidots in the nanometer scale, the behavior of superconducting cylindrical shells in the presence of a magnetic field applied parallel and perpendicular to the axis, including the dynamics of a single Abrikosov vortex trapped in these shells, and finally the magneto‐transport properties of superconducting strips with variable section at the nanoscale. [edited by author]