Non-equilibrium electron transport in mesoscale superconducting hybrids

Abstract

This thesis focusses on driven superconducting heterostructures. Both experimentally and theoretically we address the following questions: (a) how does the presence of different metallic and dielectric materials influence the electronic properties of a driven superconductor? (b) how does a non-equilibrium electron distribution arise and how does it influence the behavior of the sample? Mesoscale heterostructures offer a unique possibility to this interplay between microscopic and macroscopic behavior in a controlled environment. They are big enough for the emergence of collective macroscopic states as superconductivity or ferromagnetism. At the same time they are small compared to relevant physical length scales and therefore depend on the microscopic properties of the sample. The influence of interfaces and surfaces becomes increasingly more important and the intuitive picture in which different materials with bulk properties are connected by interfaces breaks down. Due to their small size, the samples are easily driven out of equilibrium. This leads to nonlinear behavior because collective states such as superconductivity are affected by an electronic non-equilibrium and at the same time drastically alter the thermal transport. Besides the fundamental interest, the questions asked have a direct relevance for applications. The most apparent field of use is in submillimeter photon detectors, which in many cases rely on the electrical response of a driven mesoscopic superconductor.