Electronic structure of two- and one -dimensional states on silicon

Electrons are predicted to exhibit exotic properties when confined to a single dimension. Single particles are replaced by collective excitations leading to charge and spin instabilities at low temperature. Under the proper conditions, the identity of the individual electron is lost and is replaced by independent spin and charge collective excitations. However, attaining one-dimensional systems for study remains a difficult challenge and direct evidence for spin-charge separation is lacking. Silicon surfaces provide excellent templates for engineering low-dimensional metals enabling direct study of electronic states in reduced dimensions via angle-resolved photoemission specroscopy.;In two-dimensions, gold and silver absorbates on silicon demonstrate two-dimensional metallic surface states in the band gap of the bulk states. Photoemission maps the two-dimensional Fermi surfaces and band dispersions states for the √3 x √3 and √21 x √21 noble metal reconstructions on Si(111). Noble metal dopants tailor the electronic structure, demonstrating a continuous filling of the surface state band with increasing coverage.;By growing chains of gold atoms on vicinal silicon surfaces one-dimensional states are fabricated. By changing the miscut angle and gold coverage, different chains are engineered with varying inter-chain spacing and electron count. Using high-resolution angle-resolved photoemission we map the band structures and Fermi surfaces for these atomic chains. The resulting metallic bands exhibit novel properties including a transition from two to one dimension within a single band, and back-folding at low temperature that provides initial evidence for charge density waves. From the Fermi surfaces we calculate the one-dimensional versus two-dimensional coupling strengths and demonstrate that their ratios can be tuned from 12:1 to >100:1 by increasing the chain spacing. Furthermore, the band filling increases as a function of the miscut angle. Controlling the two-dimensional coupling and band filling, along with the electron-electron interaction strength, may be key to observing spin-charge separation.