Self-assembly and topological superconductivity in antiferromagnetic ultra-thin films studied by SP-STM

Abstract

Antiferromagnetic (AFM) materials are a promising platform for new generations of ultra-fast, low energy, robust data storage and computing systems. Their combination with different substrate symmetries and properties leads to a plethora of interesting phenomena such as multi-Q states [1], [2], frustrated antiferromagnetism [3], [4] or topological nodal point superconductivity (TNPSC) [5], [6]. However, the atomic scale magnetic ordering makes their study challenging for most microscopic techniques. In this thesis I use the spin-polarized scanning tunneling microscopy (SP-STM)[7] technique to characterize the properties of AFM ultra-thin layers on substrates with different structural and superconducting properties. In the first part, the growth and magnetism of the phases in the first monolayer of Mn on Ir(111) are studied. In this system a cluster phase and reconstructed phase coexist in the sub-monolayer regime until the coverage reaches one monolayer, when the structure becomes pseudomorphic. The magnetic state of the reconstructed and pseudomorphic phases is the Néel state. In the second part, the growth, magnetism and superconductivity of Cr/Nb(110) is studied. The first layer of Cr grows pseudomorphically, the second one goes through several phases with increasing density, and the third one reaches the Cr bulk lattice constant. Regarding magnetism, just the first layer displays magnetic properties. Its magnetic ground state is the c(2 × 2) AFM state. Small strips of the first layer and the whole second layer do not develop magnetic properties such as in-gap states or magnetic order. The study of the first Cr layer on superconducting Nb(110) results in its characterization as a TNPSC.