Topological insulators is a class of material conducting on the surface and not in the bulk. In HgTe a P band is inverted with respect to an S band (negative gap): this change this semiconductor for insulator to topological insulator. A bandgap can be opened by growing it on a substrate with a lattice mismatch which strains homogenously the material. The conducting surface states lie partly in this bandbap.
Using a gated Hall device we have
- done the spectrocopy of the Dirac states in weak field magneto-transport, placing the Dirac point with a 100 microvolt accuracy
- Observed antilocalization correction to the conductivity, typical of Dirac Fermions
- analyzed the dependence of the chemical potential with density using Shubnikov deHaas frequencies.
- Observed two sets of Hall plateaus: a half odd integer serie, consistent with a single Dirac cone and an integer serie which is unexpected. An insulating phase appears at high field.
The talk will cover only a fraction of this material for pedagogical reasons.