Microwave Photocurrent From the Edge States of InAs/ GaSb and InAs/InGaSb Bilayers

We measure microwave photocurrent in devices made from InAs/GaSb and InAs/InGaSb bilays, 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 the bulk state and the edge state, we prepare two types of samples, i.e., Hall bar and Corbino disk, from the same wafer; in the latter the edge states are shunt by metal electrodes. A back gate is used to tune Fermi level into the bulk gap. Results show that the Corbino disk samples have a negligible photocurrent in the bulk gap. On the contrary we observe clear photocurrent signals from the Hall bar samples in the bulk gap. This finding suggests that the photocurrent may carry information concerning the electronic properties of the edge states. We have studed the frequency, temperature, and magnetic field dependence of the photocurrent. A brief discussion along with the data will be presented in the talk.