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. Iwill show that these topologically nontrivial states are spin polarized andthat their spin texture depends on the surface orientation.