Kidd, TE, Miller T, Chou MY, Chiang TC.
2002.
Electron-hole coupling and the charge density wave transition in TiSe2, Jun. Physical Review Letters. 88:4., Number 22
AbstractAngle-resolved photoemission is employed to measure the band structure of TiSe2 in order to clarify the nature of the (2x2x2 ) charge density wave transition. The results show a very small indirect gap in the normal phase transforming into a larger indirect gap at a different location in the Brillouin zone. Fermi surface topology is irrelevant in this case. Instead, electron-hole coupling together with a novel indirect Jahn-Teller effect drives the transition.
Chiang, TC, Chou MY, Kidd T, Miller T.
2002.
Fermi surfaces and energy gaps in Sn/Ge(111), Jan. Journal of Physics-Condensed Matter. 14:R1-R20., Number 1
AbstractOne third of a monolayer of Sn adsorbed on Ge(111) undergoes a broad phase transition upon cooling from a (root3 x root3)R30degrees normal phase at room temperature to a (3 x 3) phase at low temperatures. Since band-structure calculations for the ideal (root3 x root3)R30degrees phase show no Fermi-surface nesting, the underlying mechanism for this transition has been a subject of much debate. Evidently, defects formed by Ge substitution for Sn in the adlayer, at a concentration of just a few percent, play a key role in this complex phase transition. Surface areas near these defects are pinned to form (3 x 3) patches above the transition temperature. Angle-resolved photoemission is employed to examine the temperature-dependent band structure, and the results show an extended gap forming in k-space as a result of band splitting at low temperatures. On account of the fact that the room temperature phase is actually a mixture of (root3 x root3)R30degrees areas and defect-pinned (3 x 3) areas, the band structure for the pure (root3 x root3)R30degrees phase is extracted by a difference-spectrum method. The results are in excellent agreement with band calculations. The mechanism for the (3 x 3) transition is discussed in terms of a response function and a tight-binding cluster calculation. A narrow bandwidth and a small group velocity near the Fermi surface render the system highly sensitive to surface perturbations, and formation of the (3 x 3) phase is shown to involve a Peierls-like lattice distortion mediated by defect doping. Included in the discussion, where appropriate, are dynamic effects and many-body effects that have been previously proposed as possible mechanisms for the phase transition.
Paggel, JJ, Wei CM, Chou MY, Luh DA, Miller T, Chiang TC.
2002.
Atomic-layer-resolved quantum oscillations in the work function: Theory and experiment for Ag/Fe(100), Dec. Physical Review B. 66:4., Number 23
AbstractThe work function of atomically uniform Ag films grown on Fe(100) is measured as a function of film thickness. It shows layer-resolved variations as a result of quantum confinement of the valence electrons. A first-principles calculation reproduces the observed variations except for very thin films (one and two monolayers), and the differences can be attributed, in part, to strain effects caused by the lattice mismatch between Ag and Fe. These results illustrate the close interaction between interface effects and surface properties.
Wei, CM, Chou MY.
2002.
Theory of quantum size effects in thin Pb(111) films, Dec. Physical Review B. 66:4., Number 23
AbstractWe have carried out first-principles calculations of Pb (111) films up to 25 monolayers to study the oscillatory quantum size effects exhibited in the surface energy and work function. These oscillations are correlated with the thickness dependence of the energies of confined electrons, which can be properly modeled by an energy-dependent phase shift of the electronic wave function upon reflection at the interface. It is found that a quantitative description of these quantum size effects requires a full consideration of the crystal band structure.