Structural and Electronic Properties of In Double Layers on Si(111)√3×√3-B

Metal thin-film on semiconductor surfaces takes an important role in condensed matter physics in terms of exploring low-dimensional metallic properties. For example, thin-film of In on Si substrates has been attracting attention because of its 2-dimensional superconductivity. It was considered that In one-atom-thick on Si(111)√7×√3 surface shows relatively high Tc (3.18 K), which is quite analogous to Tc of bulk In (3.41 K).^[1] After that, it was revealed that the In layer on Si(111)√7×√3 is not one-atom-thick but double layers by a theoretical study.^[2] Despite a lot of worthful studies, it is not well understood that whether the superconductivity-related electronic properties of the In double layers basically come from an ultrathin limit of bulk In or interface effects from its substrate. Thus, it is useful to study by changing the Si(111)√7×√3 substrates to Si(111)√3×√3-B surface of In layers to identify the interfacial effects.<br/>In this study, we suggest the feasible interfacial structures of In layers on Si(111)√3×√3-B and address its electronic properties using density functional theory, within the generalized gradient approximation of exchange-correlation functional. Since the periodicity of In layers and Si substrates are different as √7×√3 and √3×√3, we introduced 3√7×√3 supercells. It is known that the B addition on the Si(111) surface induces the surface reconstruction to a √3×√3 periodicity that contains B at the subsurface and a Si adatom on each B.^[3] Interestingly, we identified that In layers can be adsorbed only on the surface that has no Si adatom, despite the presence of Si adatom in the clean surface. We also ascertained that the thickness of In layers should be 2 mono-layer from adsorption energy calculations, which coincides with the result of In/Si(111)√7×√3.^[2]<br/>To clarify the interfacial effects on the electronic structure of In double layers, we compared the band dispersion of In/Si(111)√3×√3-B and In/Si(111)√7×√3. Band unfolding method was utilized to expand the narrow first-Brillouin zone due to the supercell approach. The features of the unfolded band structure were similar among the two substrates. In addition, we calculated a band dispersion of free-standing In double layers. Detailed band dispersions and electronic structures will be discussed in the presentation.<br/>[1] T. Zhang et al., <i>Nat. Phys.</i> <b>6</b>, 104-108 (2010).<br/>[2] J. Park and M. Kang, <i>Phys. Rev. Lett.</i> <b>109</b>, 166102 (2012).<br/>[3] R. L. Headrick, I. K. Robinson, E. Vlieg, and L. C. Feldman, <i>Phys. Rev. Lett.</i> <b>63</b>, 1253-1256 (1989).