LoDiHybrids · Correlations and Proximity Effect in Low-Dimensional and Hybrid Structures

Correlations and Proximity Effect in Low-Dimensional and Hybrid Structures

Progress in nanofabrication technology has opened the door to a wide variety of novel phenomena as the sample dimensions become of the order of the relevant microscopic length scales. Research in this field is driven partly by the interest in the fundamental physics governed by quantum mechanics and partly by the ongoing miniaturization of electronic components that calls for new concepts to sustain this trend. In hybrid systems one can combine materials with different, even antagonistic properties. Through the proximity effect, the close contact between these materials leads to modifications of their properties. The project explores correlations and dynamic effects in systems in the presence of particular spin properties in systems containing magnetic materials or materials with strong spin-orbit coupling. For a long time superconductivity and ferromagnetism were believed to be mutually exclusive due to their incompatible spin properties. In hybrid structures, this incompatibility leads to a number of unusual phenomena. We studied the generation of an Andreev current by ferromagnetic resonance. Furthermore, we predicted a superharmonic long-range triplet current in diffusive bilayer ferromagnetic Josephson junctions, and we investigated the interplay of spin-singlet and spin-triplet superconducting correlations in more complex structures. Spin transport in hybrid structures is of interest in the context of the new field of “superconducting spintronics”. We showed that thermoelectric effects play an important role in understanding the non-equilibrium spin transport in Zeeman-split superconductors. The presence of spin-orbit coupling opens up new research perspectives. The search for Majorana bound states in hybrid structures containing topological insulators or nanowires with strong spin-orbit coupling is pursued very actively. On the theoretical side, the main interest is in studying signatures of the Majorana bound states and in proposing novel realizations. We investigated the AC Josephson effect in topological Josephson junctions. Specifically we elucidated the effect of the interplay between the phase dynamics and the bound state occupation dynamics in biased topological Josephson junctions on the observability of the fractional Josephson effect. We also showed that, in the presence of a magnetic field along the spin-quantization axis, topological Josephson junctions realize so-called φ0-junctions carrying an anomalous Josephson current at zero phase difference. Even in topologically trivial phases, the interplay between spin-orbit coupling and magnetic fields leads to interesting effects. We developed a quasiclassical theory of disordered Rashba superconductors admitting for a helical phase, where the superconducting phase is spatially modulated. The appearance of such a modulation is closely related to the above-mentioned possibility of realizing φ0-junctions.

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