Experimental Signatures of Topological Insulators

Abstract

Energy bands in solids describe quantum states in periodic crystals. When a quantum state is wound around the Brillouin zone, it acquires a quantum phase. For a completely filled band, the global phase acquired in this winding is a topological property of the band. For 3D solid with timereversal symmetry, there are two topological classes corresponding to a ±1 sign. A signature of topological solids (minus sign) is the presence of conducting surface states with a relativistic dispersion, similar to graphene. They can be observed in angle resolved photo-emission which is able to reconstruct their energy-momentum dispersion below the Fermi level. Some of the experimental signatures of these topological states in strained Mercury-Telluride are presented: their Dirac spectra measured at the SOLEIL synchrotron, the ambipolar sign of their surface charge carriers, the topological phase in their Landau-level quantization, and the weak-antilocalization peak in magnetotransport also controlled by the π-topological phase.