117 research outputs found
Exotic spin, charge and pairing correlations of the two-dimensional doped Hubbard model: a symmetry entangled mean-field approach
Intertwining of spin, charge and pairing correlations in the repulsive
two-dimensional Hubbard model is shown through unrestricted variational
calculations, with projected wavefunctions free of symmetry breaking. A
crossover from incommensurate antiferromagnetism to stripe order naturally
emerges in the hole-doped region when increasing the on-site coupling. Although
effective pairing interactions are identified, they are strongly fragmented in
several modes including d-wave pairing and more exotic channels related to an
underlying stripe. We demonstrate that the entanglement of a mean-field
wavefunction by symmetry restoration can largely account for interaction
effects.Comment: Minor corrections, one reference adde
Helicity Modulus and Effective Hopping in the Two-Dimensional Hubbard Model Using Slave-Boson Methods
The slave-boson mean-field method is used to study the two-dimensional
Hubbard model. A magnetic phase diagram allowing for paramagnetism, weak- and
strong ferromagnetism and antiferromagnetism, including all continuous and
first-order transitions, is constructed and compared to the corresponding phase
diagram using the Hartree-Fock approximation (HFA). Magnetically ordered
regions are reduced by a factor of about 3 along both the and density
axes compared to the HFA. Using the spin-rotation invariant formulation of the
slave-boson method the helicity modulus is computed and for half-filling is
found to practically coincide with that found using variational Monte Carlo
calculations using the Gutzwiller wave function. Off half-filling the results
can be used to compare with Quantum Monte Carlo calculations of the effective
hopping parameter. Contrary to the case of half-filling, the slave-boson
approach is seen to greatly improve the results of the HFA when off
half-filling. (Submitted to: Journal of Physics: Condensed Matter)Comment: 27 pages, LaTeX2e, 7 figures available upon request, INLO-PUB-10/9
Rhodium Doped Manganites : Ferromagnetism and Metallicity
The possibility to induce ferromagnetism and insulator to metal transitions
in small A site cation manganites Ln_{1-x}Ca_xMnO_3 by rhodium doping is shown
for the first time. Colossal magnetoresistance (CMR) properties are evidenced
for a large compositional range (0.35 \leq x < 0.60). The ability of rhodium to
induce such properties is compared to the results obtained by chromium and
ruthenium doping. Models are proposed to explain this behavior.Comment: 11 pages, 8 figure
Interplay between incommensurate phases in the cuprates
We establish the qualitative behavior of the incommensurability ,
optimal domain wall filling and chemical potential for increasing
doping by a systematic slave-boson study of an array of vertical stripes
separated by up to lattice constants. Our findings obtained in the
Hubbard model with the next-nearest neighbor hopping agree
qualitatively with the experimental data for the cuprates in the doping regime
. It is found that modifies the optimal filling and
triggers the crossover to the diagonal (1,1) spiral phase at increasing doping,
stabilized already at for .Comment: 7 pages, 4 figures, EPL styl
Magnetic ordering in the striped nickelate La5/3Sr1/3NiO4: A band structure point of view
We report on a comprehensive study of the electronic and magnetic structure
of the striped nickelate La5/3Sr1/3NiO4. The investigation is carried out using
band structure calculations based on density functional theory. A magnetic
structure compatible with experiment is obtained from spin-polarized
calculations within the generalized gradient approximation (GGA), whereas
inclusion of a local Coulomb interaction in the LDA+U framework results in a
different ground state. The influence of the various interaction parameters is
discussed in detail.Comment: 5 pages, 4 figures, 2 tables, accepted by Europhys. Let
Unconventional Hall effect in oriented CaCoO thin films
Transport properties of the good thermoelectric misfit oxide
CaCoO are examined. In-plane resistivity and Hall resistance
measurements were made on epitaxial thin films which were grown on {\it c}-cut
sapphire substrates using the pulsed laser deposition technique. Interpretation
of the in-plane transport experiments relates the substrate-induced strain in
the resulting film to single crystals under very high pressure ( 5.5 GPa)
consistent with a key role of strong electronic correlation. They are confirmed
by the measured high temperature maxima in both resistivity and Hall
resistance. While hole-like charge carriers are inferred from the Hall effect
measurements over the whole investigated temperature range, the Hall resistance
reveals a non monotonic behavior at low temperatures that could be interpreted
with an anomalous contribution. The resulting unconventional temperature
dependence of the Hall resistance seems thus to combine high temperature
strongly correlated features above 340 K and anomalous Hall effect at low
temperature, below 100 K.Comment: Submitted to Physical Review B (2005
Strongly correlated properties of the thermoelectric cobalt oxide Ca3Co4O9
We have performed both in-plane resistivity, Hall effect and specific heat
measurements on the thermoelectric cobalt oxide CaCoO. Four
distinct transport regimes are found as a function of temperature,
corresponding to a low temperature insulating one up to 63 K,
a strongly correlated Fermi liquid up to 140 K, with
and , followed
by an incoherent metal with and a high temperature insulator above
T510 K . Specific heat Sommerfeld coefficient
mJ/(mol.K) confirms a rather large value of the electronic effective mass
and fulfils the Kadowaki-Woods ratio 10 . Resistivity measurements under pressure reveal a
decrease of the Fermi liquid transport coefficient A with an increase of
as a function of pressure while the product remains constant and
of order . Both thermodynamic and transport properties suggest a strong
renormalization of the quasiparticles coherence scale of order that seems
to govern also thermopower.Comment: 5 pages, 6 figures, accepted for publication in Physical Review
Doping dependence of spin excitations in the stripe phase of high-Tc superconductors
Based on the time-dependent Gutzwiller approximation for the extended Hubbard
model we calculate the energy and momentum dependence of spin excitations for
striped ground states. Our starting point correctly reproduces the observed
doping dependence of the incommensurability in La-based cuprates and the
dispersion of magnetic modes in the insulating parent compound. This allows us
to make quantitative predictions for the doping evolution of the dispersion of
magnetic modes in the stripe phase including the energy and intensity of the
resonance peak as well as the velocity of the spin-wave like Goldstone mode. In
the underdoped regime we find a weak linear dependence of
on doping whereas the resonance energy significantly shifts to
higher values when the charge concentration in the stripes starts to deviate
from half-filling for . The velocity is non-monotonous with a
minimum at 1/8 in coincidence with a well known anomaly in . Our
calculations are in good agreement with available experimental data. We also
compare our results with analogous computations based on linear spin-wave
theory.Comment: 18 pages, 14 figures, revised and extended versio
- …