Spin-orbit split two-dimensional electron gas with tunable Rashba and Fermi energy

Abstract

We demonstrate that it is possible to tune the Rashba energy, introduced by a strong spin-orbit splitting, and the Fermi energy in a two-dimensional electron gas by a controlled change of stoichiometry in an artificial surface alloy. In the ${\mathrm{Bi}}_{x}{\mathrm{Pb}}_{1\ensuremath{-}x}∕\mathrm{Ag}(111)$ surface alloy, the spin-orbit interaction maintains a dramatic influence on the band dispersion for arbitrary Bi concentration $x$, as is shown by angle-resolved photoelectron spectroscopy. The Rashba energy ${E}_{R}$ and the Fermi energy ${E}_{F}$ can be tuned to achieve values larger than one for the ratio ${E}_{R}∕{E}_{F}$, which opens up the possibility for observing phenomena, such as corrections to the Fermi liquid or a superconducting state. Relativistic first-principles calculations explain the experimental findings.