Figure 2: Ultrafast transient absorption measurements.

(a) ΔT/T map, normalized to unity, as a function of probe wavelength λ and pump-probe delay t. The scale bar ranges from 0 to 1. The positive PB signal due to Pauli blocking rises on the 10 fs timescale due to ultrafast spreading of the electron distribution upon impulsive excitation. (b) ΔT/T dynamics at selected wavelengths of the pump-probe map. The inset shows that the onset of the signal moves to later times as the probe photon energy decreases. (c) Transient spectra at selected delays. For delays below 20 fs, the signal peaks at high photon energies due to the strongly out-of-equilibrium electron distribution. At later times (~20 fs), the signal flattens and then peaks at low photon energies, as the electron distribution thermalizes. (d) Transient dynamics at probe photon energies <1 eV. The delay in the PB onset is more evident. The recovery time slows as the electron distribution approaches the Dirac point.