Fig. 3: Transport signatures.

a Photo-induced change of source-drain current (\(\Delta {{\rm{I}}}\)) as a function of \({{{\rm{E}}}}_{{{\rm{F}}}}\) under irradiation at various peak power densities, as measured on sample C at a constant source-drain voltage of 6 mV and a cryostat temperature of 3.2 K. The photon energy is \(\hslash \varOmega=117\,{{\rm{meV}}}\). The laser beam is circularly polarized. The circles represent data points and the solid lines are the fitted curve by a Gaussian-like function described in the Methods. The dotted line marks the \({{{\rm{E}}}}_{{{\rm{F}}}}\) value corresponding to \(-{{\hslash }}\varOmega /2\), with the related uncertainty indicated by the gray stripes. b Theoretically predicted \(\varDelta I\) as calculated from the Floquet Boltzmann equation. The dotted line marks the \({E}_{F}\) value corresponding to \(-\hslash \varOmega /2\). c Depth \({a}_{0}\) of the photocurrent dip and associated error, as calculated from a Gaussian-like fit (see details in the Methods section). For both the theoretical and experimental data, \({a}_{0}\) decreases with the power density P for large P due to enhanced heating processes in the Floquet steady state. d Experimental and theoretical FWHM of the photocurrent dip and the Floquet gap size (red dotted line), \(\varDelta\), as a function of the power density. The FWHM exceeds \(\varDelta\), indicating the emergence of photoexcited electrons in the non-equilibrium Floquet steady state. The detailed error analysis of FWHM is described in the Supplementary Information. The uncertainty in the laser power density due to power fluctuation in (c) and (d) are estimated by the change in the laser power before and after each transport measurement.