The interplay of magnetism and superconductivity in one-dimensional (1D) magnetic chains on superconductors presents a promising avenue for realizing topologically protected quantum states, including Majorana zero modes (MZMs). This thesis investigates the structural, electronic and magnetic properties of rare-earth metal (REM) chains, with a particular focus on gadolinium (Gd) atoms placed on the Nb(110) surface. We demonstrate that Gd adatoms, with their large 4f magnetic moments, exhibit indirect exchange interactions mediated by their valence electrons, manifested as Yu-Shiba-Rusinov (YSR) states on the superconducting Nb(110) surface. Combining scanning tunneling microscopy and spectroscopy (STM/STS) with density functional theory (DFT) simulations, we reveal that non-collinear spin configurations could possibly arise as the magnetic ground states. These spin textures serve as an essential prerequisite for realizing topological superconductivity. Additionally, the emergence of zero-energy edge states in atomically precise Gd spin chains is investigated. Orientation-dependent differences in YSR states are revealed, where 1 1 0-oriented chains exhibit trivial edge states, while the longer 0 0 1 chains display robust zero-energy modes at their chain ends, indicative of a potential topological nature. Four-atom Gd chains in both orientations develop uniform zero-energy modes along their entire length. These experimental results emphasize the significance of chain geometry and magnetic configuration in stabilizing non-trivial edge states. We investigated other REMs to understand the role of f-shell magnetic moments on the contribution to their YSR states, including terbium (Tb), europium (Eu), cerium (Ce), and lanthanum (La), on the Nb(110) surface. While Gd and Tb chains demonstrate pronounced YSR states and robust zero-energy edge modes in the 0 0 1 orientation, Eu, Ce, and La chains fail to develop such states. With a significant diminishing of the f-shell magnetic moments, the YSR states of chains disappear, highlighting the role of the strong f-shell magnetic moments on the emergence of YSR states. Overall, this thesis provides a comprehensive analysis of the interplay between f-shell magnetism and superconductivity in 1D rare-earth chains on Nb(110) surface. The findings underscore the potential of rare-earth magnets for precise tuning of non-collinear ground states, paving the way for advancements in Majorana-based quantum systems.
Yu Wang (Thu,) studied this question.