Spin- and charge dynamics in ferromagnetic Josephson junctions

点击翻译按钮获取中文摘要

It is widely accepted that the downscaling of semiconductor devices faces fundamental physical limitations related to the heat dissipation and current leakage as well as a finite size effect in nanoscale devices. Therefore, alternative device concepts are explored. Recently, hybrid superconducting nanostructures attracted a tremendous interest, because this technology has the potential to overcome these limitations 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. In this research project, we will investigate novel spin and charge transport phenomena in superconductor (S)/ferromagnet (F) hybrid nanostructures under non equilibrium conditions. We will focus on ferromagnetic Josephson junctions (fJJs), where two superconductors are separated by a ferromagnetic barrier. The experimental determination of the current phase relation of fJJs provides direct access to their fundamental physical properties. Most studies on fJJs so far have been concerned purely with proximity effects, i.e. the influence of exchange splitting on the penetration of Cooper pairs into the F layer. However, ferromagnets also possess interesting dynamic properties, which can be explored to generate, manipulate and detect spin currents in SF heterosystems. In fJJs the dynamic coupling of the Josephson supercurrent to the magnetisation of the ferromagnetic spacer leads to novel transport phenomena. We will elucidate some of the fundamental questions related to the complex interplay of competing order parameters and in particular the question of relaxation mechanisms of non equilibrium distributions with respect to spin, charge and energy. The ultimate aim is to devise a fundamentally new concept for dissipation less spin electronic devices with unprecedented switching rates for next generation electronic circuits. 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.