  We report on a class of quantum spin Hall insulators (QSHIs) in
strained-layer InAs/GaInSb quantum wells, in which the bulk gaps are enhanced
by up to five folds as compared to the binary InAs/GaSb QSHI. Remarkably, with
consequently increasing edge velocity, the edge conductance at zero and applied
magnetic fields manifests time reversal symmetry (TRS) -protected properties
consistent with Z2 topological insulator. The InAs/GaInSb bilayers offer a much
sought-after platform for future studies and applications of the QSHI.
