197 research outputs found
Mechanism of the reorientation of stripes in the cuprates
Using the mean field theory in the slave-boson approach we analyzed the
electron correlation effects in the stripe phases. One finds that a finite
next-nearest neighbor hopping plays an important role in the low doping
regime, where it controls the crossover from the filled diagonal to half-filled
vertical/horizontal stripes at doping .Comment: 2 pages, 1 figur
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
Non-resonant Raman response of inhomogeneous structures in the electron doped Hubbard model
We calculate the non-resonant Raman response, the single particle spectra and
the charge-spin configuration for the electron doped Hubbard model using
unrestricted Hartree-Fock calculations. We discuss the similarities and
differences in the response of homogeneous versus inhomogeneous structures.
Metallic antiferromagnetism dominates in a large region of the phase
diagram but at high values of the on-site interaction and for intermediate
doping values, inhomogeneous configurations are found with lower energy. This
result is in contrast with the case of hole doped cuprates where
inhomogeneities are found already at very low doping. The inhomogeneities found
are in-phase stripes compatible with inelastic neutron scattering experiments.
They give an incoherent background in the Raman response. The signal
can show a quasiparticle-like component even when no Fermi surface is found in
the nodal direction.Comment: 8 pages, 10 figures, accepted for publication in Phys. Rev.
Spin-rotationally symmetric domain flux phases in underdoped cuprates
We propose a new form of inhomogeneous phases consisting of out-of-phase
staggered flux domains separated by diagonal charged domain walls centered on
bonds or on sites. Remarkably, such domain flux phases are spin-rotationally
symmetric and exhibit cone-like quasiparticle dispersion as well as
incommensurate order of orbital currents. Such features are consistent with the
pseudogap behavior and the diagonal stripes observed experimentally in lightly
doped cuprates. A renormalized mean field theory shows that such solutions are
competitive candidates within the -- model.Comment: 6 pages, 3 figure
Unidirectional d-wave superconducting domains in the two-dimensional t-J model
Motivated by the recently observed pattern of unidirectional domains in
high-T_c superconductors [Y. Kohsaka et al., Science 315, 1380 (2007)], we
investigate the emergence of spontaneous modulations in the d-wave
superconducting resonating valence bond phase using the t-J model at x=1/8
doping. Half-filled charge domains separated by four lattice spacings are found
to form along one of the crystal axis leading to modulated superconductivity
with out-of-phase d-wave order parameters in neighboring domains. Both
renormalized mean-field theory and variational Monte Carlo calculations yield
that the energies of modulated and uniform phases are very close to each other.Comment: 4 pages, 5 figures, minor revisions, and added reference
Microscopic origin of diagonal stripe phases in doped nickelates
We investigate the electron density distribution and the stability of stripe
phases in the realistic two-band model with hopping elements between e_g
orbitals at Ni sites on the square lattice, and compare these results with
those obtained for the doubly degenerate Hubbard model with two equivalent
orbitals and diagonal hopping. For both models we determine the stability
regions of filled and half-filled stripe phases for increasing hole doping
x=2-n in the range of x<0.4, using Hartree-Fock approximation for large
clusters. In the parameter range relevant to the nickelates, we obtain the most
stable diagonal stripe structures with filling of nearly one hole per atom, as
observed experimentally. In contrast, for the doubly degenerate Hubbard model
the most stable stripes are somewhat reminiscent of the cuprates, with
half-filled atoms at the domain wall sites. This difference elucidates the
crucial role of the off-diagonal e_g hopping terms for the stripe formation in
La_2-xSr_xNiO_4. The influence of crystal field is discussed as well.Comment: 15 pages, 12 figure
Mean-field phase diagram of interacting e_g electrons
We investigate the magnetic phase diagram of the two-dimensional model for
e_g electrons which describes layered nickelates. One finds a generic tendency
towards magnetic order accompanied by orbital polarization. For two equivalent
orbitals with diagonal hopping such orbitally polarized phases are induced by
finite crystal field.Comment: 2 pages, 2 figure
Melting of the stripe phases in the t-t'-U Hubbard model
We investigate melting of stripe phases in the overdoped regime x>0.3 of the
two-dimensional t-t'-U Hubbard model, using a spin rotation invariant form of
the slave boson representation. We show that the spin and charge order
disappear simultaneously, and discuss a mechanism stabilizing bond-centered and
site-centered stripe structures.Comment: 2 pages, 1 figur
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