Fractional Band Filling in an Atomic Chain Structure

Abstract

A new chain structure of Au is found on stepped Si(111) which exhibits a 1/4-filled band and a pair of > or =1/2-filled bands with a combined filling of 4/3. Band dispersions and Fermi surfaces for Si(553)-Au are obtained by photoemission and compared to that of Si(557)-Au. The dimensionality of both systems is determined using a tight binding fit. The fractional band filling makes it possible to preserve metallicity in the presence of strong correlations.

Chains of gold atoms with tailored electronic states

“…The optimum coverage is a single gold atom per unit cell for Si͑335͒-Au, 17 Si͑557͒-Au, 15,18,19,41 and Si͑553͒-Au. 11 Si͑775͒-Au requires more gold, almost two atoms per unit cell, similar to the two gold chains for Si(111)-5ϫ2-Au. Figure 3 compares STM images for the four related chain structures of gold on silicon: Si͑335͒-Au, Si͑557͒-Au, Si͑553͒-Au, and Si͑775͒-Au.…”

“…For example, a 1ϫ3 ordering of voids in Si͑553͒-Au is able to explain a fractional electron count of 8/3 electrons per Au atom by having two extra Si atoms in the unit cell. 11 On Si(111)5ϫ2-Au a half-filled 5ϫ4 lattice of extra Si atoms provides just the right band filling for the structure with the lowest total energy. 23,38 The optimum tunneling conditions were found at positive sample bias ͑empty states͒ in the case of Si͑557͒-Au and Si͑775͒-Au and at negative bias ͑filled states͒ for the other two structures.…”

“…These data are for a sample temperature of Ͻ100 K ͓150 K for Si͑557͒-Au͔, colder than our previously published measurements on the Si͑557͒-Au and Si͑553͒-Au surfaces. 11,15 The band dispersions in ͑for the method see Ref. 42 and 43͒.…”

“…Changing the filling from 1 2 to 1 4 and other fractional fillings may maintain the metallicity of a band even in the presence of strong interactions. 11,22 An equally important parameter for fabricating one-dimensional systems is the twodimensional coupling strength between adjacent chains, since exotic physics is predicted only in the limit of small coupling.…”

“…The band gap of silicon prevents metallic states at the Fermi surface from coupling to the substrate both in two dimensions 8,9 and in one dimension. 10,11 The Si͑111͒ surface and its vicinal surfaces ͑see Fig. 1͒ exhibit a natural tendency to form anisotropic reconstructions of metal atoms at the surface.…”