Transport and Magnetism in Mesoscopic Superconductors

TL;DR

This paper explores the quantum transport and magnetic properties of mesoscopic superconductor-normal metal hybrids, revealing new phenomena like paramagnetic instability and non-local effects, with implications for quantum computing applications.

Contribution

It provides a comprehensive analysis of single-particle signatures in mesoscopic superconducting systems, including resonance structures, magnetic screening, and unconventional Josephson effects.

Findings

Resonance structures in conductance and shot noise of NS junctions.

Discovery of paramagnetic instability in magnetic screening.

Double critical-current-flux periodicity linked to non-locality.

Abstract

Superconductivity, discovered by Kamerlingh Onnes in 1911, continues to be a fascinating subject of condensed matter physics today. Much interest has been devoted to the study of the superconductivity induced in a metal which by itself is not superconducting but is in electrical contact with a superconductor. As the carriers of superconductivity, the Cooper pairs, diffuse across the contact into the metal they remain correlated, although the pairing mechanism is lifted; we call this the proximity effect. The observation of these superconducting correlations has come within the reach of experiments in the last decade. With state-of-the-art fabrication techniques mesoscopic samples have been produced which are small and clean enough for the quantum mechanical coherence of the electrons to be preserved over the sample size. This theoretical thesis focuses on the variety of signatures of single-particle physics that appear in the electrical transport and the magnetic screening properties of these systems. We study the resonance structure in the finite voltage conductance and shot noise of NS junctions. Mapping out the H-T phase diagram of a NS hybrid layer we describe the diamagnetic screening including non-locality and impurities, the magnetic breakdown of the Meissner expulsion, and discover a paramagnetic instability towards spontaneous magnetic moments. We trace back the double critical-current-flux periodicity in ballistic SNS junctions to non-locality. Finally we exploit the Josephson relation of junctions with unconventional superconductors for the implementation of a quantum computer.