  Topological insulators (TIs) are a novel class of materials with nontrivial
surface or edge states. Time-reversal symmetry (TRS) protected TIs are
characterized by the Z2 topological invariant and their helical property
becomes lost in an applied magnetic field. Currently there exist extensive
efforts searching for TIs that are protected by symmetries other than TRS. Here
we show, a topological phase characterized by a spin Chern topological
invariant is realized in an inverted electron-hole bilayer engineered from
indium arsenide-gallium antimonide (InAs/GaSb) semiconductors which retains
robust helical edges under a strong magnetic field. Wide conductance plateaus
of 2e2/h value are observed; they persist to 12T applied in-plane magnetic
field without evidence for transition to a trivial insulator. In a
perpendicular magnetic field up to 8T, there exists no signature to the bulk
gap closing. While the Fermi energy remains inside the bulk gap, the
longitudinal conductance increases from 2e2/h in strong magnetic fields
suggesting a trend towards chiral edge transport. Our findings are first
evidences for a quantum spin Hall (QSH) insulator protected by a spin Chern
invariant. These results demonstrate that InAs/GaSb bilayers are a novel system
for engineering the robust helical edge channels much needed for spintronics
and for creating and manipulating Majorana particles in solid state.
