# II. Physikalisches Institut BDepartment of Physics

## Topological Insulators

Topological insulatorsÂ exhibit surface states which are protected by the symmetry of the insulating bulk. They cannot be detroyed by local defects at the surface. We investigate weak topological insulators which provide conducting edge states at the surface. Additionally, we probe whether phase change materials (that can be switched between crystalline and amorphous on a ns time scale) are also topological insulators in their crystalline phase. Furthermore, we prepare interfaces which potentially host Majorana Fermions (Wikipedia). These investigations are related to quantum Hall systems which also contain topologically protected states.

Central goal isÂ the imaging of topological properties on a local scale.

#### Methods

• Angle-resolved photoemission spectroscopy (ARPES) with spin-resolution
• Scanning tunneling microscopy (STM) and spectroscopy (STS)