Spin- and charge dynamics in ferromagnetic Josephson junctions

人们普遍认为，半导体器件的小型化面临着与散热和电流泄漏有关的基本物理限制以及纳米器件的有限尺寸效应。因此，探索替代装置概念。最近，混合超导纳米结构引起了极大的兴趣，因为这种技术有可能克服这些限制，甚至有望成为量子信息处理设备的新范式。然而，这种装置的实际实现需要完全理解超导和正常金属或铁磁电路元件之间的自旋和电荷电流的转移和动力学，以及这些系统中自旋和电荷自由度之间的耦合。在本研究项目中，我们将研究超导体/铁磁体混合纳米结构在非平衡条件下的自旋和电荷输运现象。我们将重点关注铁磁约瑟夫森结（fJJs），其中两个超导体被铁磁势垒分开。fjs电流相关系的实验测定提供了直接获取其基本物理性质的途径。迄今为止，大多数关于fjs的研究都只关注接近效应，即交换分裂对库珀对穿透F层的影响。然而，铁磁体还具有有趣的动态特性，可以探索在SF异质系统中产生，操纵和检测自旋电流。在fj中，约瑟夫森超电流与铁磁间隔层磁化的动态耦合导致了新的输运现象。我们将阐明与竞争顺序参数的复杂相互作用有关的一些基本问题，特别是关于自旋、电荷和能量的非平衡分布的弛豫机制问题。最终目标是为下一代电子电路设计一个具有前所未有开关率的无耗散自旋电子器件的全新概念。通过引入具有非共线磁化的自旋活性界面，可以在SF杂化体系中诱导由F中的三重态铜对携带的长距离超导对相关。最近，理论预测暗示了通过电子自旋与铁磁体磁化的动态耦合，在SF杂化系统中产生远距离三重态配对的可能性。本项目旨在通过实验研究这一新现象。目的是证明超导对相关性存在于具有长铁磁间隔的fjs中，该间隔具有通过铁磁共振诱导的空间和时间不均匀磁化。在这种特殊情况下，微波辐射下的输运实验需要检测到明显的超电流。

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.