Spin- and charge dynamics in ferromagnetic Josephson junctions

铁磁约瑟夫森结中的自旋和电荷动力学

• 批准号: 317077841
• 负责人: Professorin Dr. Elke Scheer, since 9/2018
• 金额: --
• 依托单位: Arbeitsgruppe Mesoskopische Systeme
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2016
• 资助国家: 德国
• 起止时间: 2015-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/317077841?language=en
• 关键词: Spin; charge; dynamics; ferromagnetic; Josephson

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.

人们普遍认为，半导体器件的缩小面临着与散热和电流泄漏以及纳米级器件中的有限尺寸效应相关的基本物理限制。因此，探索了替代器械概念。最近，混合超导纳米结构吸引了巨大的兴趣，因为这种技术有可能克服这些限制，甚至有望为量子信息处理设备提供新的范例。然而，这种设备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。在本研究计画中，我们将探讨在非平衡条件下，超导体（S）/铁磁体（F）混合奈米结构中新颖的自旋与电荷输运现象。我们将专注于铁磁约瑟夫森结（fJJ），其中两个超导体被铁磁势垒分开。fJJ的电流相位关系的实验测定提供了直接访问它们的基本物理性质。到目前为止，大多数关于fJJ的研究仅仅关注邻近效应，即交换分裂对库珀对穿透到F层的影响。然而，铁磁体也具有有趣的动力学性质，可以探索在SF异质系统中产生，操纵和检测自旋电流。在fJJ的动态耦合的约瑟夫森超电流的磁化的铁磁间隔导致新的运输现象。我们将阐明一些基本问题有关的复杂的相互作用的竞争秩序参数，特别是问题的松弛机制的非平衡分布相对于自旋，电荷和能量。最终目标是为下一代电子电路设计一个具有前所未有的开关速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强度的自旋活性界面，可以在SF混合系统中诱导出F中三重态库珀对所携带的长程超导对关联。最近，理论预测暗示的可能性，通过动态耦合的电子自旋的铁磁体的磁化在SF混合系统中产生长距离的三重配对。该项目旨在通过实验研究这种新现象。我们的目标是表明，超导对的相关性存在于fJJs与一个长的铁磁间隔与空间和时间上不均匀的磁化通过铁磁共振诱导。在这种特殊的情况下，一个明显的超电流应检测在微波辐射下的传输实验。