When growing HgTe on a CdTe substrate, bi-axial strain opens a gap in HgTe turning it from a semi metal into a topological insulator.  We have performed low field and high field magneto-transport in this 3D topological material.  We find that the bulk contribution to the transport current is much smaller than in any other known material.  A low field, we map the surface Dirac bands with a gated structure.
Antilocalization corrections to the conductivity have been observed and analyzed.  At high fields, there are 2 series of quantum Hall plateaus, one corresponds to a bilayer regime and the second to decoupled layers.
Experimental ways do identify the bilayer quantum Hall states are presently being pursued.