Dynamic Triplet-Supercurrent generation in Ferromagnetic Josephson Junctions

Recently, hybrid superconducting nanostructures attracted a tremendous interest, because this technology has the potential to overcome the limitations of conventional, dissipative electronic devices and even promises a new paradigm for quantum information processing devices. The practical realisation of such devices, however, requires a complete understanding of the transfer and the dynamics of spin and charge currents between superconducting and normal metal or ferromagnetic circuit elements as well as the coupling between spin and charge degrees of freedom in these systems.

Here, we investigate novel spin and charge transport phenomena in superconductor (S) –ferromagnet (F) hybrid nanostructures under non equilibrium conditions. We focus on ferromagnetic Josephson junctions (fJJs), where two superconductors are separated by a ferromagnetic barrier.

It has been established that long range superconducting pair correlations, carried by triplet cooper pairs in F, can be induced in SF hybrid systems via the introduction of spin active interfaces with a non collinear magnetisation. Recently, theoretical predictions hint to the possibility to generate long range triplet pairing in SF hybrid systems via a dynamic coupling of the electron spin to the magnetisation of the ferromagnet. This project aims to experimentally investigate this novel phenomenon. The objective is to show that superconducting pair correlations exist in fJJs with a long ferromagnetic spacer with spatially and temporally inhomogeneous magnetisation induced via a ferromagnetic resonance. In this special situation, a pronounced supercurrent should be detected in transport experiments under microwave irradiation. Moreover, the experimental determination of the current phase relation of these fJJs provides direct access to their fundamental physical properties, which are studied to evaluate the role of the spin-polarization and nature of the ferromagnetic spacer.

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Publications

1. M. Thalmann, Mesoskopische Supraleiter-Ferromagnet Heterokontakte unter Hochfrequenzeinfluss (2015)
2. M. Rudolf, Proximity-Josephson-Effekt und nichtlokale Spannungsmessungen an Supraleiter-Ferromagnet Spinventilen (2015)
3. L. Kammermeier, M. Thalmann, T. Pietsch Dynamic triplet pairing in long ferromagnetic Josephson junctions induced by FMR 628. WHS Seminar on “Trends in Mesoscopic Superconductivity” (2016) Bad Honnef (Germany)
4. Thalmann, Marcel; Pernau, Hans-Fridtjof; Strunk, Christoph; Scheer, Elke; Pietsch, Torsten, Comparison of cryogenic low-pass filters, Review of Scientific Instruments ; 88 (2017)