DETECTION OF THE LONGITUDINAL PHOTON FIELD IN SURFACE SCREENING BY PHOTOEMISSION SPECTRA

The longitudinal field component induced by the dielectric screening o f the incident radiation at the surface has recently been shown to yie ld a considerable influence on the photoemission spectra. The hydrodyn amic model for the electrodynamic surface response shows surprisingly good agreement with normal emission experimental spectra for layered d ichalcogenides. However, it is not applicable for photon frequencies b elow the plasmon energy omega(p) and was therefore extended to a two-s tep density model to simulate the multipol mode below omega(p). As a c onsequence a similar behaviour in the calculated photoemission spectra could be followed passing to low frequencies. However, the modelling of the surface is not free of parameters, sensitively depending on the rather arbitrary position of the outermost electron density steps. To relate these quantities to the real density of a layered crystal, a s elf-consistent calculation of the electrodynamic surface response, for a system with crystalline periodicity in the surface normal direction and full translational symmetry in the parallel direction, is in deve lopment. In contrast to some standard applications to the jellium mode l, Green's functions are used which prove to be very appropriate for t his actual task.