Seminarium Fizyki Materii Skondensowanej

In normal topological insulators, time-reversal symmetry and strongrelativistic (spin-orbit) effects require that the bulk insulating statesare accompanied by metallic helical Dirac-like electronic states on thesurface of the crystal. These surface states are encoded in topologicallynon-trivial wave functions of valence electrons and robustly resistnon-magnetic disorder. Recent theoretical results have suggested theexistence of a new class of topological insulators, namely topologicalcrystalline insulators (TCIs), in which crystalline symmetry replaces therole of time-reversal in ensuring topological protection of the surfacestates.I will discuss the theoretical predictions of the properties of surfaceDirac-like electrons in IV-VI TCIs and describe the experiments confirmingthe existence of TCI surface states in PbSnSe and PbSnTe mixed crystals. I will show that these topologically nontrivial states are spin polarized andthat their spin texture depends on the surface orientation.