Magnetic field-induced breakdown of helical conduction in an InAs/GaSb bilayer

We calculate the conductance of a two-dimensional bilayer with inverted electron-hole bands, to study the sensitivity of the quantum spin Hall insulator (with helical edge conduction) to the combination of the perpendicular magnetic field in presence of disorder. The characteristic breakdown field for helical edge conduction splits into two fields with increasing disorder, a field $B_c$ for the transition into a quantum Hall insulator (supporting chiral edge conduction) and a smaller field $B_c'$ for the transition to bulk conduction in a quasi-metallic regime. The spatial separation of the inverted bands, typical for broken-gap InAs/GaSb quantum wells, is essential for the magnetic-field induced bulk conduction -- there is no such regime in HgTe quantum wells.