4,404 research outputs found
Incipient quantum melting of the one-dimensional Wigner lattice
A one--dimensional tight--binding model of electrons with long--range Coulomb
interactions is studied in the limit where double site occupancy is forbidden
and the Coulomb coupling strength is large with respect to the hopping
amplitude . The quantum problem of a kink--antikink pair generated in the
Wigner lattice (the classical ground state for ) is solved for fillings
, where is an integer larger than 1. The pair energy becomes
negative for a relatively high value of , . This signals
the initial stage of the quantum melting of the Wigner lattice
Variational Wave Function for Generalized Wigner Lattices in One Dimension
We study a system of electrons on a one-dimensional lattice, interacting
through the long range Coulomb forces, by means of a variational technique
which is the strong coupling analog of the Gutzwiller approach. The problem is
thus the quantum version of Hubbard's classical model of the generalized Wigner
crystal [J. Hubbard, Phys. Rev. B 17, 494 (1978)]. The magnetic exchange energy
arising from quantum fluctuations is calculated, and turns out to be smaller
than the energy scale governing charge degrees of freedom. This approach could
be relevant in insulating quasi-one-dimensional compounds where the long range
Coulomb interactions are not screened. In these compounds charge order often
appears at high temperatures and coexists with magnetic order at low
temperatures.Comment: 4 pages, proceedings of ECRYS-200
On the checkerboard pattern and the autocorrelation of photoemission data in high temperature superconductors
In the pseudogap state the spectrum of the autocorrelation of angle resolved
photoemission (AC-ARPES) data of Bi2212 presents non-dispersive peaks in
momentum space which compare well with those responsible of the checkerboard
pattern found in the density of states by Scanning Tunneling Microscopy. This
similarity suggests that the checkerboard pattern originates from peaks in the
joint density of states, as the dispersive peaks found in the superconducting
state do. Here we show that the experimental AC-ARPES spectrum can be
reproduced within a model for the pseudogap with no charge-ordering or symmetry
breaking. We predict that, because of the competition of superconductivity and
pseudogap, in the superconducting state, the AC-ARPES data of underdoped
cuprates will present both dispersive and non-dispersive peaks and they will be
better observed in cuprates with low critical temperature. We finally argue
that the AC-ARPES data is a complementary and convenient way to measure the arc
length.Comment: 5 pages, 3 eps figure
Tight binding model for iron pnictides
We propose a five-band tight-binding model for the Fe-As layers of iron
pnictides with the hopping amplitudes calculated within the Slater-Koster
framework. The band structure found in DFT, including the orbital content of
the bands, is well reproduced using only four fitting parameters to determine
all the hopping amplitudes. The model allows to study the changes in the
electronic structure caused by a modification of the angle formed by
the Fe-As bonds and the Fe-plane and recovers the phenomenology previously
discussed in the literature. We also find that changes in modify the
shape and orbital content of the Fermi surface sheets.Comment: 12 pages, 6 eps figures. Figs 1 and 2 modified, minor changes in the
text. A few references adde
Conductivity anisotropy in the antiferromagnetic state of iron pnictides
Recent experiments on iron pnictides have uncovered a large in-plane
resistivity anisotropy with a surprising result: the system conducts better in
the antiferromagnetic x direction than in the ferromagnetic y direction. We
address this problem by calculating the ratio of the Drude weight along the x
and y directions, Dx/Dy, for the mean-field Q=(\pi,0) magnetic phase diagram of
a five-band model for the undoped pnictides. We find that Dx/Dy ranges between
0.3 < D_x/D_y < 1.4 for different interaction parameters. Large values of
orbital ordering favor an anisotropy opposite to the one found experimentally.
On the other hand D_x/D_y is strongly dependent on the topology and morfology
of the reconstructed Fermi surface. Our results points against orbital ordering
as the origin of the observed conductivity anisotropy, which may be ascribed to
the anisotropy of the Fermi velocity.Comment: 4 pages, 3 pdf figures. Fig 1(b) changed, one equation corrected,
minor changes in the text, references update
Orbital differentiation and the role of orbital ordering in the magnetic state of Fe superconductors
We analyze the metallic (pi,0) antiferromagnetic state of a five-orbital
model for iron superconductors. We find that with increasing interactions the
system does not evolve trivially from the pure itinerant to the pure localized
regime. Instead we find a region with a strong orbital differentiation between
xy and yz, which are half-filled gapped states at the Fermi level, and
itinerant zx, 3z^2-r^2 and x^2-y^2. We argue that orbital ordering between yz
and zx orbitals arises as a consequence of the interplay of the exchange energy
in the antiferromagnetic x direction and the kinetic energy gained by the
itinerant orbitals along the ferromagnetic y direction with an overall
dominance of the kinetic energy gain. We indicate that iron superconductors are
close to the boundary between the itinerant and the orbital differentiated
regimes and that it could be possible to cross this boundary with doping.Comment: 6 pages, including 7 figures. As accepted in Phys. Rev.
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