1,721,014 research outputs found
Checkerboard and stripe inhomogeneities in cuprates
No full textWe systematically investigate charge-ordering phases by means of a restricted and unrestricted Gutzwiller approximation to the single-band Hubbard model with nearest- (t) and next-nearest- (t(')) neighbor hopping. When parallel to t(')/t parallel to is small, as appropriate for La2-xSrxCuO4, stripes are found, whereas in compounds with larger parallel to t(')/t parallel to (such as Ca2-xNaxCuO2Cl2 and Bi2Sr2CaCu2O8+delta) checkerboard structures are favored. In contrast to the linear doping dependence found for stripes the charge periodicity of checkerboard textures is locked to 4 unit cells over a wide doping range. In addition we find that checkerboard structures are favored at surfaces
Dynamics of Electronic Inhomogeneities in Cuprates
No full textA phenomenological model is constructed which can reconcile the simultaneous existence of low-energy Bogoljubov quasiparticles and high-energy electronic order as observed by scanning tunneling microscopy (STM) experiments in cuprates. The theory can account for the high-energy contrast reversal in the STM spectra between positive and negative bias as characteristic for charge-density wave scattering. On the other hand the low-energy Fourier-transform of the local density of states is an even function of bias which provides an alternative to the formation of pair-density waves
Dynamical charge and spin density wave scattering in cuprate superconductors
No full textWe show that a variety of spectral features of high-Tc cuprates can be understood on the basis of the coupling of charge carriers to some kind of dynamical order that we exemplify in terms of fluctuating charge and spin density waves. Two theoretical models that capture different aspects of such a dynamical scattering are investigated. The first approach leaves the ground state in the disordered phase but couples the electrons to bosonic degrees of freedom, corresponding to the quasi-singular scattering associated with closeness to an ordered phase. The second, more phenomological approach starts from the construction of a frequency-dependent order parameter that vanishes for small energies. Both theories capture scanning tunneling microscopy and angle-resolved photoemission experiments that suggest the protection of quasi-particles close to the Fermi energy but the manifestation of long-range order at higher frequencies
Influence of correlations on transitive electron-phonon couplings in cuprate superconductors
No full textWe investigate a model for the CuO2 plane of high-T-c superconductors where the charge carriers are coupled to A(1g) and B-1g symmetric out-of plane vibrations of the oxygen atoms in the presence of local Hubbard correlations. The coupling is implemented via a modulation of the hopping integral and we calculate the renormalization of vertex and pairing scattering functions based on the time-dependent Gutziller approximation. Contrary to local electron-phonon couplings we find that the transitive coupling can even be enhanced by correlations for certain momenta and symmetries of the vibrations. While this effect may be important for certain properties, we find that, with regard to superconductivity, electron-electron correlations still generically lead to a suppression of the pairing correlations. Our results allow for an estimate of correlation effects on the electron-phonon induced pair scattering from weak electron-electron interactions up to the Mott regime. For onsite repulsions relevant to cuprate superconductors our calculations reveal a significant contribution of B-1g phonons to d-wave superconductivity
Fermi surface and electronic structure of incommensurate charge-density wave systems
No full textWe study the single-particle spectra of a model that shows an incommensurate charge-density wave (CDW) instability arising from the competition between phase separation and long-range Coulomb interactions. Starting from an open Fermi surface, we find that the resulting CDW is oriented along the (1, 0) and (or) (0, 1) direction, which allows for a purely one-dimensional (1D) or a two-dimensional (2D) eggbox type charge modulation. In both cases, the van Hove singularities are substantially enhanced, and the spectral weight of Fermi surface states near the M points tends to be suppressed. Remarkably, a leading edge gap arises near these point, which, in the eggbox case, leaves finite arcs of the Fermi surface gapless. © 2000 Plenum Publishing Corporation
Striped phases in the two-dimensional Hubbard model with long-range Coulomb interaction
No full textWe investigate the formation of partially filled domain walls in the two-dimensional Hubbard model in the presence of a long-range interaction. Using an unrestricted Gutzwiller variational approach we show that (i) the strong local interaction favors charge segregation in stripe domain walls, (ii) the long-range interaction favors the formation of half-filled vertical stripes with a period doubling due to the charge and a period quadrupling due to the spins along the watt. Our results show that, besides the underlying lattice structure, also the electronic interactions can contribute to determine the different domain wall textures observed in Nd-doped copper oxides and nickel oxides. [S0163-1829(98)03540-1]
Fermi surface and photoemission lineshape of incommensurate CDW systems
No full textWe study the single-particle spectra of a model which shows an incommensurate charge-density wave (CDW) instability arising from the competition between phase separation and long-range Coulomb interactions. Starting from an open Fermi surface we find that the resulting CDW is oriented along the (1,0)- and (or) (0,1)-direction which (besides a purely one-dimensional structure) allows for a two-dimensional "eggbox type" charge modulation. This leads to a substantial enhancement of the van Hove singularities and the spectral weight of Fermi surface states near the M-points tends to be suppressed. Remarkably, a leading edge gap arises near these points, which, in the eggbox case, leaves finite arcs of the Fermi surface gapless. Extending this approach to the inclusion of dynamic incommensurate CDW fluctuations in the superconducting state we calculate the photoemission lineshape which agrees well with experimental data of underdoped Bi2212 compounds
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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