  Transport measurements are performed on InAs/GaSb double quantum wells at
zero and finite magnetic fields applied parallel and perpendicular to the
quantum wells. We investigate a sample in the inverted regime where electrons
and holes coexist, and compare it with another sample in the non-inverted
semiconducting regime. Activated behavior in conjunction with a strong
suppression of the resistance peak at the charge neutrality point in a parallel
magnetic field attest to the topological hybridization gap between electron and
hole bands in the inverted sample. We observe an unconventional Landau level
spectrum with energy gaps modulated by the magnetic field applied perpendicular
to the quantum wells. This is caused by strong spin-orbit interaction provided
jointly by the InAs and the GaSb quantum wells.
