22 research outputs found
Superconductivity with hard-core repulsion: BCS-Bose crossover and s-/d-wave competition
Full text linkWe consider fermions on a 2D lattice interacting repulsively on the same site
and attractively on the nearest neighbor sites. The model is relevant, for
instance, to study the competition between antiferromagnetism and
superconductivity in a Kondo lattice. We first solve the two-body problem to
show that in the dilute and strong coupling limit the s-wave Bose condensed
state is always the ground state. We then consider the many-body problem and
treat it at mean-field level by solving exactly the usual gap equation. This
guarantees that the superconducting wave-function correctly vanishes when the
two fermions (with antiparallel spin) sit on the same site. This fact has
important consequences on the superconducting state that are somewhat unusual.
In particular this implies a radial node-line for the gap function. When a next
neighbor hopping t' is present we find that the s-wave state may develop nodes
on the Fermi surface.Comment: 10 pages, 9 fig
Optical properties of MgH2 measured in situ in a novel gas cell for ellipsometry/spectrophotometry
Get PDFThe dielectric properties of alpha-MgH2 are investigated in the photon energy
range between 1 and 6.5 eV. For this purpose, a novel sample configuration and
experimental setup are developed that allow both optical transmission and
ellipsometric measurements of a transparent thin film in equilibrium with
hydrogen. We show that alpha-MgH2 is a transparent, colour neutral insulator
with a band gap of 5.6 +/- 0.1 eV. It has an intrinsic transparency of about
80% over the whole visible spectrum. The dielectric function found in this work
confirms very recent band structure calculations using the GW approximation by
Alford and Chou [J.A. Alford and M.Y. Chou (unpublished)]. As Pd is used as a
cap layer we report also the optical properties of PdHx thin films.Comment: REVTeX4, 15 pages, 12 figures, 5 table
