Transport in mesoscopic superconducting devices
Licentiate thesis, 2019

A field of growing interest within the last few decades is the study of superconductivity in mesoscopic-scale heterostructures. Mesoscopic refers to sizes between the atomic and macroscopic scales. Here, the size of heterostructures can be comparable to the inherent scale of superconductivity, the superconducting coherence length, and give rise to new physical phenomena.

The focus of this work is on mesoscopic hybrid structures consisting of superconducting, normal-metal, and magnetic regions. The combination of these different types of materials and the competition between interactions such as magnetism and superconductivity can then be used to design structures with novel effects. This is not only interesting from a fundamental point of view but equally relevant for technological applications. The magnet-superconductor hybrid structures examined in this work, for example, give rise spin-polarized Andreev bound states, a promising ingredient to superconducting spintronics.

We study transport in such hybrid systems under current bias to investigate the effects of such Andreev bound states on nonequilibrium properties. As part of this work, we develop a general calculation scheme for current-bias nonequilibrium within the quasiclassical theory of superconductivity. We use this scheme to study charge and spin imbalance in a normal-metal/superconductor structure with a spin-active interface. Our results show that transport in systems with spatially extended tunnel barriers is more accurately described by this current-bias picture compared to a voltage-bias description traditionally used in the theoretical literature for narrow constrictions. We find that the presence of Andreev bound states at a spin-active interface between normal-metal and superconducting regions strongly influence the charge as well as spin transport in such structures.

superconductivity

quasiclassical theory

mesoscopic physics

nonequilibrium superconductivity

Andreev bound states

superconducting spintronics

MC2 Seminarierum Hbar (C511)
Opponent: Thilo Bauch

Author

Kevin Marc Seja

Chalmers, Microtechnology and Nanoscience (MC2), Applied Quantum Physics

Areas of Advance

Nanoscience and Nanotechnology (2010-2017)

Roots

Basic sciences

Infrastructure

C3SE (Chalmers Centre for Computational Science and Engineering)

Subject Categories

Condensed Matter Physics

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology: 428

Publisher

Chalmers University of Technology

MC2 Seminarierum Hbar (C511)

Opponent: Thilo Bauch

More information

Latest update

1/13/2020