Fig. 4: Nano-photocurrent with Cherenkov phonons.

Second-order demodulated nano-photocurrents (\({{{\rm{PC}}}}_{{{\bf{2}}}}\)) were taken under different DC current scanned along the same middle line of the graphene device with carrier densities p = 3.3 × 10¹²cm⁻² for (a) and n = −4.4 × 10¹²cm⁻² for (b). Similar to the presentation of Fig. 3a, b the y-axes indicate the scanning positions and cartoons of carriers indicated the flow directions. The vertical dashed gray line marks the zero-bias data. The cartoons of moving carriers with arrows indicate the different velocity directions of electrons and holes. a, b share the same color bar. The four colored dots in the middle of (b) marked the positions where data in (c) were taken. c DC current dependent nano-photocurrent line profiles taken from different positions in (b). The dashed orange curve represents anticipated bolometric photocurrent extracted from the simultaneously taken transport experiment. The black dashed arrow marks the amount of PTE (photo-thermoelectric) current without current bias. The insets demonstrated the corresponding scenarios of effective tip-gating effect, where \({{{\rm{V}}}}_{{{\bf{0}}}}\), \({{{\rm{V}}}}_{{{\bf{1}}}}\) and \({{{\rm{V}}}}_{{{\bf{1}}}}{{{\prime} }}\) represents backgate voltage, bias voltage and local potential of graphene. Light blue, purple and dark blue represent hBN, graphene, and additional gate dielectric layers of the sample stacks. Purple arrows animate the Cherenkov phonon emission.