Showing papers by "Mark S. Hybertsen published in 1988"

Electronic band structure of CaBi 2 Sr 2 Cu 2 O 8

Abstract: The band structure for body-centered tetragonal ${\mathrm{CaBi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8}$ has been calculated in the local-density--functional approach by the linearized muffin-tin--orbital method with the atomic-sphere approximation. This is the undistorted, stoichiometric parent compound to the recently reported 84-K superconductor. The main band features at the Fermi level include a pair of nearly half-filled two-dimensional Cu-O 3d-2p bands similar to those found in the previous Cu-O planar superconductors as well as a pair of slightly filled Bi 6p bands that provide additional carriers in the Bi-O planes.

Geometric and local electronic structure of Si(111)-As.

Abstract: The Si(111)-As surface is imaged by scanning tunneling microscopy under UHV conditions. A threefold-symmetric 1 x 1 structure is observed, consistent with models suggesting substitution of As for Si in the outer half of the top double layer. No evidence for residual stacking faults on the scale of the 7 x 7 mesh is detected, but atomic debris, interpreted as displaced Si atoms, is seen. I-V characteristics of the junction show features separated by 1.9--2.3 eV consistent with an empty surface state in the projected gap and a filled state resonance with the bulk as predicted by self-energy calculations for this surface.

Theory of quasiparticle surface states in semiconductor surfaces

Abstract: A first-principles theory of the quasiparticle surface-state energies on semiconductor surfaces is developed. The surface properties are calculated using a repeated-slab geometry. Many-body effects due to the electron-electron interaction are represented by the electron self-energy operator including the full surface Green's function and local fields and dynamical screening effects in the Coulomb interaction. Calculated surface-state energies for the prototypical Si(111):As and Ge(111):As surfaces are presented. The calculated energies and dispersions for the occupied surface states (resonances) are in excellent agreement with recent angle-resolved photoemission data. Predictions are made for the position of empty surface states on both surfaces which may be experimentally accessible. The resulting surface state gap at \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} for Si(111):As agrees with recent scanning-tunneling-spectroscopy measurements. Comparison of the present results to eigenvalues from the local-density-functional calculation reveals substantial corrections for the gaps between empty and occupied surface states. This correction is found to depend on the character of the surface states involved.

Monolayer growth and structure of ga on si(111)

Abstract: The vertical position of Ga on Si(111) for coverages in the monolayer range has been quantitatively established using the x-ray standing-wave technique. The experimentally determined position is in good agreement with first-principles total energy minimization calculations using the local-density functional approach. Gallium atoms substitute for silicon in the outer half of the (111) double layer at the surface. The low-energy electron-diffraction pattern shows an incommensurate superstructure which is not associated with Ga adsorbed in the substitutional sites, but with Ga weakly bound to the surface.

Calculation of the many body interaction parameters in the highTc compound La2CuO4

Abstract: The energy surface as a function of local Cu d-charge and in plane O p-charge fluctuation is calculated using the constrained local density functional approach. This is done in a supercell geometry using the LMTO-ASA method. The energy surface is then mapped onto a self consistent mean field solution of the two-band Hubbard model thus obtaining the on-site Cu and O Coulomb interaction ( U d , U p ) as well as the intersite interaction ( U pd ). Implications of the calculated values of U i on various pairing models are briefly discussed.

Calculation of the Hubbard-Type Many Body Interaction Parameters using Constrained Density Functional Theory

Abstract: The constrained density functional approach is used to calculate the energy surface as a function of local charge fluctuations in La2CuO4. This energy surface is then mapped onto a self consistent mean field solution of the Hubbard model which allows extraction of the Coulomb interaction parameters when combined with oneelectron parameters derived from band structure results. The present calculations indicate that La2CuO4 is intermediate between the extreme spin or charge fluctuation regimes. This severly restricts the range of parameter space for theories of quasiparticles, optical excitations and possible pairing mechanism based on the extended Hubbard model.

The Self Energy Approach for Calculation of Quasiparticle Energies in Materials Systems

Abstract: A self energy approach directly taking into account the many-body nature of the electron-electron interaction is described which gives an excellent account of the quasiparticle band energies in semiconductors and insulators. The self energy approach provides a crucial link between structural models and spectroscopic probes of materials systems. Applications to bulk semiconductors, semiconductor surfaces and short period superlattices are described. A model for the screened Coulomb interaction can reduce the amount of computation required. Applicability of bulk self energy results to more complex systems, e.g. surfaces, is discussed.