Displaceable magnetic skyrmions in ultrathin films on superconductors for configurable Majorana state

孤立的skyrmion对磁存储器特别感兴趣，因为它们可以通过低电流密度移动，并且拓扑稳定性增强。它们已在广泛的多晶金属多层材料中被观察到。然而，在这些多晶金属薄膜中，由于固定在结构缺陷上，离子的迁移率经常受到限制。对于外延薄膜，只有少数系统是已知的稳定磁天空。在这些结构中，空间反演对称性在整体中被晶体结构本身破坏，如MnSi，或被Fe/Ir（111）等界面破坏。在这些系统中，在大磁场（1 ~ 3t）下报道了孤立的天幕。我们最近发现Co/Ru（0001）中的磁skyrmions在磁场消失时是元稳定的，并且可以用磁性STM尖端观察时移动。然而，Ru在低于500 mK和低于7 mT的磁场下具有超导性，并且有人认为，在传统超导体和显示Skyrmions的磁膜之间的界面上形成了Majorana费米子。本项目的主要目标是实现和理论上描述Co/Ru（0001）或相关系统中的马约拉纳态，借助STM对观测到的skyrmions和相关马约拉纳态进行横向位移，了解横向位移的机制，研究磁层中的邻近效应和马约拉纳态的演化。最终，将研究马约拉纳态的纠缠和马约拉纳零模式的编织，以研究在Co/Ru中使用skyrmions作为拓扑量子计算的潜力。这个项目依赖于实验和理论的密切配合。合作伙伴之前曾在材料系统的纯磁性方面进行过合作。

Isolated skyrmions are of particular interest for magnetic memories since they can be moved by low current densities and their topologically enhanced stability. They have been observed in a wide range of polycrystalline metallic multilayers. However, in these polycrystalline metallic films, skyrmion mobility is often limited by pinning to structural defects. For epitaxial films, only few systems are known to stabilize magnetic skyrmions. Among them are the structures where the spatial inversion symmetry is broken in the bulk by the crystal structure itself, as in MnSi, or by interfaces such as Fe/Ir(111). In these systems, isolated skyrmions were reported under large magnetic fields (1 to 3 T). We recently discovered that magnetic skyrmions in Co/Ru(0001) are meta stable down to vanishing magnetic fields and can be moved when observed with magnetic STM tip. Ru is, however, superconducting below 500 mK and at magnetic fields below 7 mT, and it has been suggested that at the interface between a conventional superconductor and magnetic films displaying Skyrmions, Majorana fermions are formed. The main objectives of this project is to realize and theoretically describe Majorana states in the hybrid non-collinear magnetic-superconducting system Co/Ru(0001) or related systems, to laterally displace the observed skyrmions and associated Majorana states with help of STM, to understand the mechanism of the lateral displacement, to investigate the proximity effect in the magnetic layer and the evolution of the Majorana states. Ultimately, the entanglement of Majorana states and the braiding of the Majorana zero modes will be studied in order to investigate the potential to use skyrmions in Co/Ru as for topological quantum computing. The project relies on a close collaboration between experiment and theory. The partners have collaborated on the purely magnetic aspects of the materials system, before.