Fig. 3: Intra sideband delay evaluation of tungsten valence band photoelectrons around 62 eV.

a Magnified view of the RABBITT-spectrogram in Fig. 1c around 62 eV. The dashed boxes represent the energy-dependent shape of each sideband. b For each sideband, we retrieved the delays at its central, highest, and lowest energies (black circles). Note the asymmetric character of the sideband at 60 eV just below the resonance (see text). Calculated classical electron transport time to the crystal surface is indicated by the red line, the group-velocity-based simulation of transport delays by a blue solid line. As the simulation is based on the maximum group velocities at each final energy, contributions from other bands can lead to higher delays (blue filled area). Error bars represent the SD over all traces in each dataset (see “Methods”). c Band energies for electrons photoemitted perpendicularly to the surface (black lines). The classical free-electron dispersion curve is shown in red; the bands with maximum group velocity at each energy are highlighted in blue. The latter are notably more shallow at 60–62 eV, which translates to lower group velocity and therefore higher photoemission delay in b.