Acoustic detection of high-resistance states in gated bilayer graphene devices

Applying a perpendicular electric field to bilayer graphene (BLG) induces an electrically tunable bandgap, so that insulating states with resistances exceeding ∼10⁸ Ω can be generated. These high-resistance states pinch off the conducting channel, thereby enabling high-quality gated devices for classical and quantum electronics. However, it is challenging to precisely quantify these states electrically due to their high resistances, especially when different areas of the device are operated in different high-resistance states. Here, taking advantage of the strong acoustoelectric effect, we demonstrate the detection of these high-resistance states in a multi-gated BLG device using surface acoustic waves. Under different gating configurations, the device is operated in different high-resistance states. Although these states have similar resistances of ∼10⁸ Ω, we show their acoustoelectric responses exhibit pronounced differences, thereby allowing the acoustic detection. More interestingly, we demonstrate that when the conducting channel is pinched off by one top gate, we are still able to acoustically, but not electrically, detect the gating effect of another top gate. Our results reveal the powerful capability and the promising future of acoustically characterizing BLG and other two-dimensional materials, especially their electronic states with high resistances.