3,073 research outputs found
Absence of superconductivity in the half-filled band Hubbard model on the anisotropic triangular lattice
We report exact calculations of magnetic and superconducting pair-pair
correlations for the half-filled band Hubbard model on an anisotropic
triangular lattice. Our results for the magnetic phases are similar to those
obtained with other techniques. The superconducting pair-pair correlations at
distances beyond nearest neighbor decrease monotonically with increasing
Hubbard interaction U for all anisotropy, indicating the absence of
frustration-driven superconductivity within the model.Comment: 4 pages, 4 EPS figure
Spin exchange and superconductivity in a model for two-dimensional quarter-filled systems
The effect of antiferromagnetic spin fluctuations on two-dimensional
quarter-filled systems is studied theoretically. An effective model on
a square lattice which accounts for checkerboard charge fluctuations and
next-nearest-neighbors antiferromagnetic spin fluctuations is considered. From
calculations based on large-N theory on this model it is found that the
exchange interaction, , increases the attraction between electrons in the
d channel only, so that both charge and spin fluctuations work
cooperatively to produce d pairing.Comment: 9 pages, 6 figure
Comparison of the phase diagram of the half-filled layered organic superconductors with the phase diagram of the RVB theory of the Hubbard-Heisenberg model
We present an resonating valence bond (RVB) theory of superconductivity for
the Hubbard--Heisenberg model on an anisotropic triangular lattice. We show
that these calculations are consistent with the observed phase diagram of the
half-filled layered organic superconductors, such as the beta, beta', kappa and
lambda phases of (BEDT-TTF)_2X [bis(ethylenedithio)tetrathiafulvalene] and
(BETS)_2X [bis(ethylenedithio)tetraselenafulvalene]. We find a first order
transition from a Mott insulator to a d_{x^2-y^2} superconductor with a small
superfluid stiffness and a pseudogap with d_{x^2-y^2} symmetry. The
Mott--Hubbard transition can be driven either by increasing the on-site Coulomb
repulsion, U, or by changing the anisotropy of the two hopping integrals, t'/t.
Our results suggest that the ratio t'/t plays an important role in determining
the phase diagram of the organic superconductors.Comment: 4 pages, 3 figur
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