Perpendicular Emission, Dichroism, and Energy Dependence in Angle-Resolved Photoemission: The Importance of The Final State

Angle-resolved photoemission spectroscopy has been developed to a very high accuracy. However, effects that depend sensitively on the state of the emitted photoelectron were so far hard to compute for real molecules. We here show that the real-time propagation approach to time-dependent density functional theory allows us to obtain final-state effects consistently from first principles and with an accuracy that allows for the interpretation of experimental data. In a combined theoretical and experimental study we demonstrate that the approach captures three hallmark effects that are beyond the final-state plane-wave approximation: emission perpendicular to the light polarization, circular dichroism in the photoelectron angular distribution, and a pronounced energy dependence of the photoemission intensity.

Figure 1

ARPES maps corresponding to the PTCDA highest occupied molecular orbital (HOMO). Left: plane-wave result; middle: experiment; right: real-time propagation result.

Figure 2

ARPES maps corresponding to the PTCDA HOMO at $\hslash \omega =20\mathrm{eV}$ (a) and 50 eV (c). Upper row: real-time propagation. Lower row: experiment. Within each panel, LCP spectra are on the left and RCP on the right. Middle panel (b): geometry.

Figure 3

CDAD intensities for the CO molecule for $\beta =50°$ and $\varphi =90°$; the black dash-dotted line shows the data [66] from Westphal et al.