It has been proposed that the Si(557)-Au surface exhibits spin-charge separation in a one-dimensional electron liquid. Two narrowly spaced bands are found which exhibit a well-defined splitting at the Fermi level. That is incompatible with the assignment to a spinon-holon pair in a Luttinger liquid. Instead, we propose that the two bands are associated with two nearly degenerate atomic chains, or a chain of step atoms with two broken bonds. Such an assignment explains why the surface is metallic despite an even number of electrons per unit cell.

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Unusual electronic states are found for gold-induced chain and ladder structures on vicinal Si͑111͒ surfaces, such as Si(111)5ϫ2-Au and Si͑557͒-Au. As two-dimensional reference the Si(111)ͱ3ϫͱ3-Au surface is investigated. The highly stepped Si͑557͒-Au surface is metallic, despite an even electron count. That is explained by two half-filled, nearly degenerate bands. On the Si(111)5ϫ2-Au surface we find a band that changes continuously from one dimensional at its maximum to two dimensional at its minimum. It exhibits a pseudogap within 0.3 eV of the Fermi level E F , where the spectral weight is strongly reduced. Si(111)ͱ3 ϫͱ3-Au exhibits an electron pocket at ⌫ that changes its filling continuously with increasing Au coverage.

A strong, gold-induced surface state is found on single-domain Si(111)-(5x2)-Au at low temperatures. Its band dispersion is one dimensional near the Fermi level E(F) and gradually becomes two dimensional towards the bottom of the band, thus providing a model for a continuous transition in dimensionality. A Peierls-like gap is observed in the one-dimensional portion of the band near E(F).