Photon energy dependent circular dichroism in angle-resolved photoemission from Au(111) surface states

We performed angle-resolved photoemission experiments on Au(111) surface with circularly polarized light. Data were taken with photon energies in the range between 20 and 100 eV in order to investigate the photon energy dependent behavior in the circular dichroism (CD). While the magnitude of the normalized CD value varies with a maximum value of about 70%, the sign of CD does not change for the photon energy within the range, inconsistent with the prediction based on the density-functional theory (DFT) calculation. Our calculation of the CD using DFT initial state and free electron final state shows a better consistency with experimental results than an earlier study using the inverse low-energy electron diffraction state as the final state. We briefly discuss the dominating factor that determines the CD from Au(111) states.

Figure 1

(a) Experimental geometry and schematic Fermi surfaces of Au(111) surface states. Au(111) surfaces are in the $xy$ plane. Angle between sample normal direction ($\widehat{z}$) and incident photon $\xi$ is ${50}^{\circ }$ in this work. (b) Fermi surface (FS) data taken with 55-eV photon. (c) From left, RCP, LCP, and RCP-LCP data along the $k_x=0$, taken with 21-eV photon, respectively.

Figure 2

Left panels of (a)–(d) are RCP-LCP mapping data at 20 meV binding energy measured with photon energy 29, 40, 55, and 82 eV, respectively. Right panels are RCP-LCP cut data along the $k_x=0$ cut (dashed line in left panels).

Figure 3

(a) Averaged normalized CD (NCD) at $(k_x,k_y)=(0,k_F^{\mathrm{out}})$ and ($0,k_F^{\mathrm{in}}$) points taken with photon energy from 20 to 100 eV. (b),(c) Constant energy CD map at 20 meV binding energy taken with 31 and 32 eV photon, respectively.

Figure 4

DFT calculation in $20–100$ eV photon energy with ${45}^{\circ }$ incident photon. The outer band wave vector ($k_F^{\mathrm{out}}$) is 0.176 ${\%}^{-1}$ and inner band wave vector ($k_F^{\mathrm{in}}$) is 0.154 ${\%}^{-1}$.

Figure 5

Calculated CD-ARPES for grazing incident ($\xi ={90}^{\circ }$) photons in $20–100$-eV range. The CD signal in the grazing incident case represents in-plane OAM contribution.

Figure 6

Calculated CD-ARPES for normal incident ($\xi =0^{\circ }$) photons in $20–100$-eV range. CD taken with normal incident photons should show the out-of-plane OAM contribution. Note that the color scale used in this figure is not the same as those used in Figs. 4 and 5.