  Inverted-gap GaSb/InAs quantum wells have long been predicted to show quantum
spin Hall insulator (QSHI) behavior. The experimental characterization of the
QSHI phase in these systems has relied on the presence of quantized edge
transport near charge neutrality. However, experimental data showing the
presence of edge conductance in the \emph{trivial} regime suggest that
additional experimental signatures are needed to characterize the QSHI phase.
Here we show that electric field- induced gap oscillations can be used as an
indicator of the presence of helical edge states in system. By studying a
realistic low-energy model GaSb/InAs quantum wells derived from $k \cdot p$
band theory, we show that such oscillations are bound to appear in narrow
samples as the system is driven to the the the topological phase by the
electric field. Our results can serve as a guide for the search of additional
experimental signatures of the presence of topologically-protected helical edge
states in GaSb/InAs systems.
