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 $t'$ 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 $x\simeq 1/16$.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 t−t′t-t' Hubbard model

We calculate the non-resonant Raman response, the single particle spectra and the charge-spin configuration for the electron doped $t-t'$ 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 $U-n$ 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 $B_{2g}$ 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 $t$--$J$ 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