Mariana Weissmann

Electronic structure of the mercury-based high-Tc compound with four CuO2 layers: HgBa2Can−1CunO2n+2 (n = 4)

Abstract The electronic structure of the tetragonal mercury-based compound containing four CuO2 planes, HgBa2Ca3Cu4O10 (Hg1234), has been made from first principles, within the local-density approximation using the full potential linear muffin-tin orbital method. The Hg-derived band which dopes the CuO2 planes dips further below the Fermi energy than in the compounds with n = 2 and 3 planes (this band stays above the Fermi energy for n = 1), increasing the degree of Hg character of all sheets of the Fermi surface.

Ab initio calculations of electronic band structure, nesting features of the Fermi surface and frozen phonons in the infinite layer cuprates

Abstract Electronic band structure, frozen phonons and some approximations to the electron-phonon interactions for the “infinite layer” cuprates CaCuO 2 and SrCuO 2 are studied by the full potential linear muffin tin orbital method (FP-LMTO). Differences and similarities with other cuprates studied by the same method are analyzed.

Are surface effects to be included in the study of the electronic structure of high temperature superconductors

A first principles determination of surface effects on the electronic structure of Bi2201 is presented. We show that these effects will modify the Local Density Approximation (LDA) answer to the electronic structure of Bi2201 and thus should be considered if a comparison is made to surface sensitive experimental findings.

Electronic structure, nesting features and van Hove singularities in the mercury-based high Tc compounds containing 1 to 5 CuO2 layers

Abstract A systematic study of the band structure, Fermi surface, density of states and the q dependence of the electronic susceptibility has been performed from first principles within the local density approximation using the Full Potential Linear Muffin Tin Orbital Method (LMTO) for HgBa 2 Ca n −1 Cu n O 2 n +2 ( n = −5). A comparisson for the whole series is presented. Hole doping by addition of O in the O (4) site in the Hg plane or the effect of pressure can be modeled by moving E F close to the van Hove singularities. Changes of the nesting features with this modeled hole doping or pressure are discussed.

Alloy model for high-temperature superconductors

Abstract An alloy model is proposed for the electronic structure of high-temperature superconductors. It is based on the assumption that holes and extra electrons are localized in small copper-oxygen clusters, that would be the components of such an alloy. This model, when used together with quantum chemical calculations on small clusters, can explain the structure observed in the experimental densities of states of both hole and electron superconductors close to the Fermi energy. The main point is the strong dependence of the energy level distribution and composition on the number of electrons in a cluster. The alloy model also suggests a way to correlate T c with the number of holes, or extra electrons, and the number of adequate clusters to locate them.

Surface effects on the electronic structure of Bi2201

Abstract Results are presented of a first principles determination of surface effects on the electronic structure of the cuprate superconductor Bi2201 within the Local Density Approximation (LDA). The inclusion of the surface introduces surface related states. The dispersion characteristics are such that the calculated bands are close to those predicted in recent angular resolved photoemission experiments on Bi2201. We conclude that surface termination effects need to be included in theoretical studies to make direct comparison with experimental results.

Electronic structure of Bi2Sr2CuO6 (Bi2201) : description of the copper-oxygen bands close to the Fermi energy

Photoemission results in the cuprate superconductors [1] show that close to the Fermi energy and aroundM point flat copper-oxygen bands with small bismuth contribution appear in an extended region. In this paper we determine from first principles the bandstructure of Bi2201 using the FP-LMTO method within the LDA. We show that the position relative to the Fermi energy and the dispersion of the calculated copper-oxygen bands are dependent on surface effects. Surface reconstruction is also analyzed.

Electronic energy bands of Bi2+χSr2−χCan−1CunO2n+4

Band structure, first principles, LMTO full-potential calculations within the LDA are performed and compared with experimental photoemission results for the n = 1 and n = 2 compounds. Close to the Fermi energy and centered around the M point of the Brillouin zone, the experiments show an extended k-space region with very flat copper oxygen bands with small bismuth contribution. The position of the calculated LDA bands with respect to the Fermi energy and the dispersion is very dependent on the different occupations and the results seem crystallographic structure, observed by x-ray studies. This is simulated in our calculations and the results seem to improve agreement with experiments.