Transport and spectral properties of low-dimensional superconductors in the presence of spin-dependent fields.

Abstract

he interplay between superconductivity and spin-dependent fields is known to lead to striking phenomena, like critical field enhancement, magnetoelectric effects and the appearance of Yu-Shiba-Rusinov bound states at magnetic impurities. In this thesis, we investigate these effects in low dimensional systems.We first demonstrate that the combination of both spin-orbit and Zeeman fields in superconducting one-dimensional systems leads to the appearance of an inhomogeneous phase at low magnetic field and high critical temperature. We show that the ground state corresponds to a zero-current state where the current stemming from spin-orbit coupling, called anomalous charge current, is exactly compensated by the current coming from the wave-vector of the superconducting order parameter. We also discuss how it is possible to predict the appearance of the anomalous current from symmetry arguments based on the SU(2)-covariant formalism.In a second part, we consider a type-II superconducting thin film in contact with a Néel skyrmion. The skyrmion induces spontaneous currents in the superconducting layer, which under the right condition generate a superconducting vortex in the absence of external magnetic fields. We compute the magnetic field and current distributions in the superconducting layer in the presence of the Néel skyrmion.In the last part of this thesis, we focus on the appearance of Yu-Shiba-Rusinov states in the superconducting crystal ß-Bi2Pd. We propose effective models in order to explain recent experimental results showing a double spatial oscillation of the local density of states at Shiba energy. We demonstrate that the minimal condition to reproduce this double oscillation is the presence of two superconducting channels connected via a hopping term or via a magnetic impurity. These effective models can be easily generalized to describe the spectrum of multiband superconductors with magnetic impurities.