  We measure microwave photocurrent in devices made from InAs/GaInSb bilayers
where both insulating bulk state and conducting edge state were observed in the
inverted-band regime, consistent with the theoretical prediction for a quantum
spin Hall (QSH) insulator. It has been theoretically proposed that microwave
photocurrent could be a unique probe in studying the properties of QSH edge
states. To distinguish possible photoresponse between bulk state and helical
edge state, we prepare Hall bar and Corbino disk from the same wafer. Results
show that the Corbino disk samples have a negligible photocurrent in the bulk
gap while clear photocurrent signals from the Hall bar samples are observed.
This finding suggests that the photocurrent may carry information concerning
the electronic properties of the edge states.
