Exploring tunable magnet/superconductor hybrid quantum systems via scanning tunneling microscopy

• Applicant: Dr. Roberto Lo Conte, Ph.D.
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2021 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459025680

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.

• DFG Programme: Research Grants