Topological insulators and Rashba systems

Unoccupied surface band structure of a topological insulator from measurements and calculations. From Niesner et al., PRB 2014.

In traditional semiconductors, electronic properties like the band structure and the charge transport are widely independent of the electron spin. This is different in ‘spintronics’, which aim to design highly efficient devices by manipulating electron spins. Therefore, materials are needed in which a spin polarization can be generated, transported, and ultimately switched.

Both topological insulators and Rashba systems have spin-polarized rather than spin-degenerate electronic bands, even though they are not magnetic. In topological insulators, the spin-polarized states are metallic and localized at the surface of an, ideally insulating, bulk material. Rashba systems have semiconducting spin-polarized bands, which can occur both at surfaces or in bulk materials.

We use angle-resolved photoelectron spectroscopy to study the electronic structure of new Rashba systems and topological insulators. Femtosecond time-resolved experiments are applied to investigate the fundamental electron and spin dynamics in these systems. Techniques using circularly polarized light have proven particularly useful for this purpose. The research is done within an international network of collaborations with theoretical physicists and experts in crystal growth