Evolution of the Rashba spin-orbit-split Shockley state on Ag/Pt(111)

We have studied the evolution of the Pt(111) Shockley-type surface state, which can be described as a surface resonance upon deposition of Ag monolayers. We have combined angle-resolved photoemission and scanning-tunneling-spectroscopy measurements with electronic-structure and photoemission calculations for true semi-infinite systems to guarantee a complete description of all surface-sensitive spectral features. An unusual energy shift and a considerable Rashba-type spin-orbit splitting of the surface resonance were observed and are discussed in terms of modifications in the electronic structure and relationship between the semi-infinite bulk and the surface potential via multiple electron scattering. The maximum magnitude of the splitting in momentum space amounts to $0.051\pm 0.007$ Å${}^{-1}$ and appears as one of the highest values so far observed in the $\mathrm{\Gamma ̄}$-type surface-state-resonance bands.

Figure 1

Dispersion of the Pt(111) Shockley surface state obtained by electronic-structure calculations. Left panel: Color-scale intensity map; right panel: dispersion of the momentum distribution curve maxima (circles) approximated by a parabolic fit using Eq. (20) (solid line).

Figure 2

Room-temperature STM images ($60\times 60$ nm${}^2$) of (a) 1.5 ML and (b) 2.5 ML Ag thin films deposited on Pt(111). (c) Differential conductivity curves measured by STS in the different Ag-covered surface regions. The curve maxima give the energy position of the surface resonance.

Figure 3

Surface-resonance bands obtained by ARPES measurements (left panels) and by first-principles calculations (right panels) on Pt(111) surfaces covered by 1, 2, and 3 monolayers, respectively. The ARPES data have been recorded at normal emission along the $\mathrm{\Gamma ̄}$-$\mathrm{K̄}$ direction and at $T=50$ K. For 1 ML, the inset shows the ARPES intensity map divided by the Fermi function. The band dispersions are approximated by parabolic curves (dashed red lines).