Exploring tunable magnet/superconductor hybrid quantum systems via scanning tunneling 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。在超导衬底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，衬底的超导状态预计会影响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，预测拓扑保护电子态将出现在异质界面上，从而允许拓扑超导性的出现。本项目主要通过自旋极化扫描隧道显微镜（SP-STM）研究新的MSH量子系统。沉积磁层中的原子自旋结构将被成像为温度和磁场的函数，从而了解超导性对超薄膜中建立的磁相的影响。此外，扫描隧道光谱（STS）将用于研究混合系统的电子特性，并揭示拓扑超导性的出现。电子特性将在物理（纳米结构的边缘）和磁（畴壁）边界的位置进行表征，以试图区分拓扑电子状态的不同可能起源。这种调查将在两种不同类型的MSH系统上进行。最初的研究将在由具有单层和双层磁性的大块超导体组成的材料系统上进行。随后，研究将转向稍微复杂的系统，在初始磁体/超导系统的界面上插入一层非常薄的第二超导材料的中间层。目的是了解初始MSH系统的特性如何通过邻近效应通过第二超导材料的存在来调整。整个系统的超导转变温度是多少？能否通过改变超导中间层的厚度来调整转变温度和三层的量子特性？作为材料和中间层厚度的函数，自旋织构是如何变化的？不同拓扑超导态能否通过改变中间层来稳定？这些是本研究项目将试图回答的一些关键科学问题。

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 ultrathin magnetic layer hosting non-collinear spin-textures. On the one hand, the superconducting state of the substrate is expected to influence the magnetic phase established in the ultrathin magnet. On the other hand, topologically protected electronic states 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.This project focuses on the investigation of new MSH quantum systems via spin-polarized scanning tunnelling microscopy (SP-STM). The atomic spin texture in the deposited magnetic layers will be imaged as a function of temperature and magnetic fields, allowing to understand the influence of superconductivity on the magnetic phase established in the ultra-thin film. In addition, scanning tunnelling spectroscopy (STS) will be used to investigate the electronic properties of the hybrid system and to unveil the emergence of topological superconductivity. The electronic properties will be characterized at the location of physical (edges of nanostructures) as well as magnetic (domain walls) boundaries, in the attempt to distinguish among the different possible origins of topological electronic states. This kind of investigation will be done on two different types of MSH systems. The initial study will be conducted on materials systems consisting of a bulk superconductor with on top magnetic monolayers and double-layers. Subsequently, the study will move towards slightly more complex systems, where a very thin interlayer of a second superconducting material will be inserted at the interface of the initial magnet/superconductor system. The aim is to understand how the properties of the initial MSH system can be tuned by the presence of a second superconducting material via proximity effects. What will be the superconducting transition temperature of the whole system? Can the transition temperature and so the quantum properties of the trilayer be tuned by changing the thickness of the superconducting interlayer? How does the spin-texture change as a function of the material and the thickness of the interlayer? Can different topological superconducting states be stabilized by changing the interlayer? These are some of the key scientific questions that this research project will try to answer.