Topological Insulators

par David Carpentier (ENS Lyon, Lyon, France)

lundi 13 mai 2013, 14:30 → 15:30 Europe/Paris

ICS

Seminaire du Consortium de Physique Theorique de Strasbourg (CPTS)

New phases of matter, called topological insulators, have been recently discovered. In this talk, I will give a pedagogical introduction to a few of their properties. These phases are analog to the quantum Hall effects : they are insulating in the bulk, but possess an order which is not conventional and not associated to a broken symmetry. Indeed this order is related to the twisted topology of the ensemble of electronic wavefuntions and is called a topological order. A key consequence of this topological order is the existence of metallic states at the surface of these materials. In the case of the quantum Hall effects, these surface states are chiral, with a propagation direction imposed by the strong magnetic field. The new topological insulators are induced by a strong spin-orbit instead of a magnetic field. This origin manifests itself in the nature of the surface states : they correspond to pairs of states with opposite spins propagating in opposite directions, and are analogous to the low energy Dirac states of graphene. I will describe experimental realizations and tests of these new phases, with a particular interest to their transport properties.