Minigaps and the quantum Hall effect in broken gap InAs/GaSb heterostructures

Abstract

InAs/GaSb heterojunctions offer the unique situation in a semiconductor of overlapping conduction and valence bands. A wavevector dependent minigap occurs due to the anticrossing of the electron and hole dispersion relations. As a result the resistivity increases strongly in very pure intrinsic structures due to the reduction in the electron group velocity. Applying a magnetic field parallel to the layers shifts the conduction and valence band relative to each other in k-space and the structure turns back to an indirect semimetal. As a result we can observe a giant negative magnetoresistance. Interband absorption is observed across the minigap, and this can also be removed by the parallel field which transforms the system to an indirect band gap alignment. In high perpendicular magnetic fields strong oscillations occur in the Hall coefficient, and at low temperatures a series of zero Hall resistance states are found in which a divergence of the diagonal resistivity occurs at the same point as a zero in the Hall resistance.