Extended Data Fig. 6: Extraction of μ in imaging experiment.

a, b, Examples of extracting μ (at E=0.56 V/nm) at the representative pixel ‘R’ (a) and at a different sample location (b). The black curves are the spatial dependent characteristic response curves. At each ν and E, we kept ‘R’ at the set point through a feedback loop; the reflection count at each pixel was recorded (red dots). We then recorded the reflection counts at four additional bottom gate voltages near the set point (blue, orange and green dots). The characteristic response curves are then shifted horizontally to match to the five data points for each ν. The dashed lines correspond to 60 % reflectance contrast of the response curves. At each ν, we use the bottom gate voltage at the intersection of the dashed line and the response curve to obtain μ.