Tuning the Spin-Orbit Coupling and the Spin Dynamics of Atomic Chains on Superconductors

The ever-growing demand for high-performance computational power can no longer be met by the miniaturization of existing Si-based integrated circuit technology. New approaches that replace the electrical charge as the information carrier such as nanospintronics or overall new computing schemes such as quantum computation are promising technological routes to address these issues and are at the heart of modern physics research. While research towards quantum computation has made large leaps forward in recent years, it also became apparent that the decoherence time of the so-far realized qubits is too short. A heavily pursued approach to solve this issue is the use of topologically protected qubits that rely on exotic non-Abelian Majorana bound states (MBS), which can be realized as excitations in condensed-matter systems e.g. at the boundaries of topological superconductors. This Ph.D. thesis addresses the experimental realization and fundamental properties of both technological concepts (nanospintronics and topological qubits) in the platform of artificial atomic spin chains assembled on the surfaces of s-wave superconductors. The methods of scanning tunneling microscopy (STM) and - spectroscopy (STS) are employed to construct such chains and different operational modes are used to investigate their magnetic and electronic properties as well as their spin dynamics. The experiments are carried out in a setup with a base temperature of 320 mK and an external magnet capable of applying a 12 T magnetic field. Three material systems are investigated in the course of this thesis in order to determine suitable properties for the realization of MBS in spin chains on superconductors. These properties are closely linked to the local bound states that magnetic adatoms induce in superconductors - Yu-Shiba-Rusinov (YSR) states - as well as their magnetic and electronic interactions in ensembles of multiple adatoms, which give rise to Shiba bands. The first material platform investigated in this thesis are single adatoms, ...