Transport phenomena in superconducting hybrid nanostructures

TL;DR

This thesis explores charge and thermal transport phenomena in superconducting nanostructures, employing advanced theoretical methods to analyze various hybrid systems and their responses to external stimuli.

Contribution

It develops a comprehensive theoretical framework for understanding transport in superconducting nanostructures, including subgap, thermal, and microwave-irradiated phenomena.

Findings

Analysis of subgap transport in SIF structures

Development of a theory for microwave-irradiated SQPCs

Application of Keldysh Green functions to superconducting transport

Abstract

This PhD thesis is divided in 6 chapters. In chapter 1 we introduce basic superconducting phenomena. Such as, the BCS theory, the Andreev reflection and the proximity effect, and the charge current transport in superconducting tunnel junctions. In chapter 2 we present the Keldysh nonequilibrium Green function formalism used to obtain the results of this thesis, together with clarifying examples corresponding to simple junctions. In chapter 3, the subgap transport properties of a SIF structure are studied. We devote chapter 4 to the study of thermal transport in superconducting nanohybrid structures. In chapter 5, we develop a general theory for the microwave-irradiated high-transmittance superconducting quantum point contact (SQPC), which consists of a thin constriction of superconducting material in which the Andreev states can be observed. The thesis concludes with a summary of the obtained results in chapter 6. The detailed derivation of the quasiclassical equations is presented in the appendix.