Tailoring of spin-split metallic surface-state bands on silicon

To exploit Rashba effect in a two-dimensional electron gas on silicon surface for spin devices, it is necessary to have spin-split metallic surface-state bands. However, metals with strong spin-orbit coupling (e.g., Bi, Tl, Sb, Pt) induce reconstructions on silicon with almost exclusively spin-split insulating bands. We suggest to add a second adsorbate to these reconstructions in order to get spin-split metallic bands on silicon. The second adsorbate can affect the surface band structure in two ways. First, it can donate electrons to the available spin-split empty-state insulating or shallow metallic bands converting them to the well-defined metallic bands with enhanced electron filling. Corresponding example systems are Au/Si(1 1 1)3 × 3 modified by In, Tl, Na or Cs and Tl/Si(1 1 1) modified by extra Tl adsorption. Second, by alloying a metal with a strong spin-orbit coupling with the other suitable metal one can obtain a dense two-dimensional alloy layer on silicon which electron band structure contains spin-split metallic bands. For example, this possibility was realized by alloying Bi/Si(1 1 1)3 × 3 reconstruction with Na and Tl/Si(1 1 1)1 × 1 reconstruction with Pb. The suggested approach allows creation of the metallic surface-state bands with various spin textures on silicon and therefore enhances the possibility to integrate fascinating and promising capabilities of spintronics with current silicon-based technologies.