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Séminaire « Propriétés optiques et électroniques des nanostructures » de l’INSP

Experimental determination of the sign of the band gap in a topological insulator - Badih A. Assaf, 18 octobre 2016 à 11 h

INSP - UPMC - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Badih A. Assaf, Junior Research Chair fellowship at ENS-Paris, LPA, magnetooptic group

Abstract

The topological character of a semiconductor is governed by the parity of the conduction and valence band. In topological insulators, band topology is non-trivial, since the parity of the conduction and valence bands appears to be inverted compared to commonly known semiconductors. Under certain symmetry consideration, this inverted band parity leads to topological surface states (TSS). No experimental assessment of this band inversion can be made using conventional experimental probes, apart from the observation of topological surface states, upon its occurrence. We tackle this problem and show that in any massive Dirac systems obeying the Bernevig-Hughes-Zhang Hamiltonian for topological insulators, the topological character of the system, or equivalently the sign of its band-gap, can be experimentally determined by a precise measurement of the Fermi velocity. We demonstrate this by performing magnetooptical infrared Landau level spectroscopy on topological crystalline insulator Pb1-xSnxSe (0