459 research outputs found
Pseudogap Formation in Models for Manganites
The density-of-states (DOS) and one-particle spectral function of the one- and two-orbital models for manganites, the latter with
Jahn-Teller phonons, are evaluated using Monte Carlo techniques. Unexpectedly
robust pseudogap (PG) features were found at low- and
intermediate-temperatures, particularly at or near regimes where
phase-separation occurs as 0. The PG follows the chemical potential
and it is caused by the formation of ferromagnetic metallic clusters in an
insulating background. It is argued that PG formation should be generic of
mixed-phase regimes. The results are in good agreement with recent
photoemission experiments for .Comment: Accepted for publication in Phys. Rev. Lett., 4 pages, Revtex, with 4
figures embedde
Spin-flux phase in the Kondo lattice model with classical localized spins
We provide numerical evidence that a spin-flux phase exists as a ground state
of the Kondo lattice model with classical local spins on a square lattice. This
state manifests itself as a double-Q magnetic order in the classical spins with
spin density at both and and further exhibits fermionic
spin currents around an elementary plaquette of the square lattice. We examine
the spin-wave spectrum of this phase. We further discus an extension to a face
centered cubic (FCC) lattice where a spin-flux phase may also exist. On the FCC
lattice the spin-flux phase manifests itself as a triple-Q magnetically ordered
state and may exist in -Mn alloys.Comment: 5 pages, 3 figure
Robust D-wave Pairing Correlations in a Hole-Doped Spin-Fermion Model for Cuprates
Pairing Correlations are studied numerically in the hole-doped spin-fermion
model for cuprates. Simulations performed on up to 12x12 clusters provide
robust indications of D-wave superconductivity away from half-filling. The
pairing correlations are the strongest in the direction perpendicular to the
dynamic stripe-like inhomogeneities that appear in the ground state at some
densities. An optimal doping, where the correlations reach a maximum value, was
observed at about 25% doping, in qualitative agreement with hight T_{c}
cuprates' experiments. On the other hand, pairing correlations are suppressed
by static stripe inhomogeneities.Comment: 4 pages, 4 figure
Resonating valence bond wave function for the two dimensional fractional spin liquid
The unconventional low-lying spin excitations, recently observed in neutron
scattering experiments on , are explained with a spin
liquid wave function. The dispersion relation as well as the wave vector of the
incommensurate spin correlations are well reproduced within a projected BCS
wave function with gapless and fractionalized spin-1/2 excitations around the
nodes of the BCS gap function. The proposed wave function is shown to be very
accurate for one-dimensional spin-1/2 systems, and remains similarly accurate
in the two-dimensional model corresponding to , thus
representing a good ansatz for describing spin fractionalization in two
dimensions.Comment: 5 pages, 4 figures. To appear in Phys. Rev. Let
A Monte Carlo Method for Fermion Systems Coupled with Classical Degrees of Freedom
A new Monte Carlo method is proposed for fermion systems interacting with
classical degrees of freedom. To obtain a weight for each Monte Carlo sample
with a fixed configuration of classical variables, the moment expansion of the
density of states by Chebyshev polynomials is applied instead of the direct
diagonalization of the fermion Hamiltonian. This reduces a cpu time to scale as
compared to for the
diagonalization in the conventional technique; is the dimension
of the Hamiltonian. Another advantage of this method is that parallel
computation with high efficiency is possible. These significantly save total
cpu times of Monte Carlo calculations because the calculation of a Monte Carlo
weight is the bottleneck part. The method is applied to the double-exchange
model as an example. The benchmark results show that it is possible to make a
systematic investigation using a system-size scaling even in three dimensions
within a realistic cpu timescale.Comment: 6 pages including 4 figure
Charge transfer in heterostructures of strongly correlated materials
In this manuscript, recent theoretical investigations by the authors in the
area of oxide multilayers are briefly reviewed. The calculations were carried
out using model Hamiltonians and a variety of non-perturbative techniques.
Moreover, new results are also included here. They correspond to the generation
of a metallic state by mixing insulators in a multilayer geometry, using the
Hubbard and Double Exchange models. For the latter, the resulting metallic
state is also ferromagnetic. This illustrates how electron or hole doping via
transfer of charge in multilayers can lead to the study of phase diagrams of
transition metal oxides in the clean limit. Currently, these phase diagrams are
much affected by the disordering standard chemical doping procedure, which
introduces quenched disorder in the material.Comment: 14 pages, 9 figures. Invited article for a special issue of JPCM on
Metal Oxide Thin Films; minor changes in the tex
Anomalous enhancement of spin Hall conductivity in superconductor/normal metal junction
We propose a spin Hall device to induce a large spin Hall effect in a
superconductor/normal metal (SN) junction. The side jump and skew scattering
mechanisms are both taken into account to calculate the extrinsic spin Hall
conductivity in the normal metal. We find that both contributions are
anomalously enhanced when the voltage between the superconductor and the normal
metal approaches to the superconducting gap. This enhancement is attributed to
the resonant increase of the density of states in the normal metal at the Fermi
level. Our results demonstrate a novel way to control and amplify the spin Hall
conductivity by applying an external dc electric field, suggesting that a SN
junction has a potential application for a spintronic device with a large spin
Hall effect.Comment: 5 pages, 4 figures, To be published as a Rapid Communication in
Physical Review
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