Fig. 4: Laser intensity and temperature dependence of the longitudinal conductance.
a Longitudinal photocurrent as a function of \({{{\rm{E}}}}_{{{\rm{F}}}}\) at a fixed source-drain voltage of 6 mV, with laser spot in focus and defocused. For all three curves, the laser power is ~3.6 W, corresponding to a peak power density of 0.6 mW/μm2 at focus. Under defocused irradiation, with the laser spot slightly moved to the side, the power density drops by ~3 times (gray curves). Circular polarization of 10.6 μm wavelength laser radiation. The cryostat temperature stabilized at ~3.4 K. b Theoretically calculated photocurrent for weak drives, exhibiting shallower dips near resonance as a function of decreasing driving power, in agreement with (a). c Temperature dependence of the longitudinal photocurrent as a function of \({{{\rm{E}}}}_{{{\rm{F}}}}\). The photocurrent decreases, and the dips at \({{{\rm{E}}}}_{{{\rm{F}}}}=\,\pm \hslash \varOmega /2\) disappear at high temperatures. The laser beam is circularly polarized. d Theoretically calculated photocurrent for laser power density 1.4 mW/μm2, the photocurrent dip becomes less visible at higher temperatures. The dotted lines in (a–d) mark the \({{{\rm{E}}}}_{{{\rm{F}}}}\) value corresponding to \(\pm {{\hslash }}\varOmega /2\), where the related uncertainty is indicated by the gray stripes in (a) and (c).
