  We report on the coexistence of both normal and topological insulating phases
in InAs/GaSb bilayer quantum well induced by the built-in electric field tuned
optically and electrically. The emergence of topological and normal insulating
phases is assessed based on the evolution of the charge carrier densities, the
resistivity dependence of the gap via in-plane magnetic fields and the thermal
activation of carriers. For the Hall bar device tuned optically, we observe the
fingerprints associated with the presence of only the topological insulating
phase. For another Hall bar processed identically but with an additional top
gate, the coexistence of normal and topological insulating phases is found by
electrical tuning. Our finding paves the way for utilizing a new
electro-optical tuning scheme to manipulate InAs/GaSb bilayer quantum wells to
obtain trivial-topological insulating interfaces in the bulk rather than at the
physical edge of the device.
