Quantum phenomena in spin physics: from spin interference to the nature of time

The spin of electronic states in solids provides an enthralling playground to study fundamental quantum phenomena, especially if spin-orbit interaction is included. We explore such effects in our spin- and angle-resolved photoemission experiments where we can measure the 3D spin polarisation vector for any point of the band structure. It will be shown how the coherent superposition of spin states in, for example, Rashba systems and topological insulators leads to a spin polarisation in the plane perpendicular to what would be expected classically. The understanding of such processes allows us to take these effects to a next level and measure the fundamental time scale of a quantum transition. It will be experimentally shown that these time scales are in the order of attoseconds and differ with the strength of interactions. These findings allow us to philosophise about the fundamental nature of time and its role in quantum mechanics