Disorder and magnetic-field-induced breakdown of helical edge conduction in an inverted electron-hole 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 electrostatic disorder and a perpendicular magnetic field. The characteristic breakdown field for helical edge conduction splits into two fields with increasing disorder, a field Bc 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 quasimetallic 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.