Theory of the overlayer plasmon on the Si(001)2×1-K surface

The dispersion of the overlayer plasmon on Si(001)2×1-K surface is investigated theoretically based on structure models in which alkali-metal adatoms form one-dimensional chains on the ridge of Si dimers. First, a simplified rod model is introduced to clarify qualitative features of the overlayer plasmon in such systems. Then a first-principles band-structure calculation is performed to elucidate the detailed electronic structure of Si(001)2×1-K surface. Based on the surface bands obtained, the dispersion of the overlayer plasmon on this surface is calculated nonempirically by the use of the random-phase approximation. The interband plasmon mode between K 4s–like and K 4$p_x$–like bands is found to reproduce the observed plasmon dispersion very well.