Photon energy dependence of circular dichroism of the Au(111) surface state

Abstract

Through relativistic photoemission calculations for the Au(111) surface state at the Fermi level, we study the photon energy dependence of circular dichroism. The dichromatic signal (${D}_{S}$) pattern changes 23 times with photon energies between 7 and 100 eV, and we have found 13 different patterns in the ${k}_{\ensuremath{\parallel}}$ map at the Fermi level for the ${D}_{S}$ from the Au(111) surface state with normal incidence light. We show that the photon energy dependence of ${D}_{S}$ is very complex even in the simplest case. The sign change in the circular dichroism as a function of photon energy is related to the relative phases of the complex expansion coefficients of different outgoing partial waves in a time-reversed low-energy electron diffraction state. With off-normal incidence, the $z$ component of the incoming photon field is dominant, and the fine structure seen in the ${D}_{S}$ in the normal incidence case is lost very rapidly, moving from a normal to an off-normal incidence. We also report that the Rashba split surface state of Au(111) has a significant component of $d$-type orbital due to relativistic effects and the computational setup used.