Exploring tunable magnet/superconductor hybrid quantum systems via spin-polarized low energy electron microscopy

近年来，量子材料的研究正经历着前所未有的加速发展，这主要是由于量子信息技术在未来的应用前景。磁体/超导体混合（MSH）系统是设计具有可调谐性能的新型量子材料的非常有前途的候选者。在超导基板和承载非共线自旋织构的超薄磁层之间的界面上，有望出现丰富的新物理现象。一方面，有报道称基片的超导状态可以控制在超薄磁体中建立的磁相。另一方面，由于非共线自旋织构和超导相之间的相互作用，预计拓扑保护电子态和等自旋三重态将出现在异质界面上，从而允许拓扑超导和自旋极化超电流的出现。本文提出使用低温自旋极化低能电子显微镜（SPLEEM）来研究MSH量子系统。SPLEEM的独特功能将允许以纳米分辨率表征沉积的磁性薄膜和多层中的完整三维自旋织构，作为温度的函数（低于和高于超导临界温度），目的是了解超导对磁性层中稳定自旋织构的影响。所有这一切都将通过利用最近在加州劳伦斯伯克利国家实验室安装的低温SPLEEM的独特功能成为可能，这是唯一一个在液体He温度下工作的SPLEEM，并向外部用户开放。将研究两种不同类型的MSH系统。最初，研究将集中在MSH系统上，其中大块超导体与磁性超薄薄膜和多层膜相连接。这个项目初始阶段的目标是发现承载非共线自旋纹理的材料系统，以及温度如何影响它们的磁基态。随后，我将研究更复杂的系统，在初始MSH系统的界面处插入一层大型自旋轨道耦合材料的薄夹层。目的是了解初始MSH系统的性质如何通过存在大的自旋轨道耦合中间层来调整。

In recent years the investigation of quantum materials has been experiencing an unprecedented acceleration, mostly due to the promise of applications in the upcoming quantum information technologies. Magnet/superconductor hybrid (MSH) systems are very promising candidates for designing new quantum materials with tunable properties. Rich new physics is expected to emerge at the interface between a superconducting substrate and an ultra-thin magnetic layer hosting non-collinear spin textures. On the one hand, it has been reported that the superconducting state of the substrate can control the magnetic phase established in the ultra-thin magnet. On the other hand, topologically protected electronic states and equal-spin triplets are predicted to be present at the hetero-interface due to the interplay between the non-collinear spin texture and the superconducting phase, allowing for the emergence of topological superconductivity and spin-polarized supercurrents.Here I propose to use low temperature spin-polarized low energy electron microscopy (SPLEEM) to investigate MSH quantum systems. The unique capabilities of SPLEEM will allow the characterization of the full 3-dimentional spin texture in the deposited magnetic thin films and multilayers with nanometer resolution as a function of temperature (below and above the superconducting critical temperature), with the aim of understanding the influence of superconductivity on the stabilized spin textures in the magnetic layers. All this will be possible by exploiting the unique capabilities of the recently installed low temperature SPLEEM at the Lawrence Berkeley National Laboratory in California, which is the only SPLEEM functioning at liquid He temperature and open for access to external users.Two different types of MSH systems will be investigated. Initially, the study will focus on MSH systems where a bulk superconductor is interfaced with magnetic ultra-thin films and multilayers. The goal of this initial phase of the project will be to discover materials systems hosting non-collinear spin textures and how temperature affects their magnetic ground state. Subsequently, I will study more complex systems, where a thin interlayer of a large spin-orbit coupling material will be inserted at the interface of the initial MSH system. The aim is to understand how the properties of the initial MSH system can be tuned by the presence of the large spin-orbit coupling interlayer.