A. Aligia
Universidad Nacional de Cuyo, Instituto Balseiro, Faculty Member
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Using numerical diagonalization of a 4x4 cluster, we calculate on-site s, extended s and d pairing correlation functions (PCF) in an effective generalized Hubbard model for the cuprates, with nearest-neighbor correlated hopping and next... more
Using numerical diagonalization of a 4x4 cluster, we calculate on-site s, extended s and d pairing correlation functions (PCF) in an effective generalized Hubbard model for the cuprates, with nearest-neighbor correlated hopping and next nearest-neighbor hopping t'. The vertex contributions (VC) to the PCF are significantly enhanced, relative to the t-t'-U model. The behavior of the PCF and their VC, and signatures of anomalous flux quantization, indicate superconductivity in the d-wave channel for moderate doping and in the s-wave channel for high doping and small U.
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Using numerical diagonalization of a 4×4 cluster, we calculate on-site s, extended-s, and dx2-y2 pairing correlation functions (PCF's) in an effective generalized Hubbard model for the cuprates, with nearest-neighbor correlated... more
Using numerical diagonalization of a 4×4 cluster, we calculate on-site s, extended-s, and dx2-y2 pairing correlation functions (PCF's) in an effective generalized Hubbard model for the cuprates, with nearest-neighbor correlated hopping and next-nearest-neighbor hopping t'. The vertex contributions to the PCF's are significantly enhanced, relative to the t-t'-U model. The behavior of the PCF's and their vertex contributions, and signatures of anomalous flux quantization, indicate superconductivity in the d-wave channel for moderate doping and in the s-wave channel for high doping and small U.
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We perform an extensive study of Sr_{3}Cr_{2}O_{7}, the n=2 member of the Ruddlesden-Popper Sr_{n+1}Cr_{n}O_{3n+1} system. An antiferromagnetic ordering is clearly visible in the magnetization and the specific heat, which yields a huge... more
We perform an extensive study of Sr_{3}Cr_{2}O_{7}, the n=2 member of the Ruddlesden-Popper Sr_{n+1}Cr_{n}O_{3n+1} system. An antiferromagnetic ordering is clearly visible in the magnetization and the specific heat, which yields a huge transition entropy, Rln(6). By neutron diffraction as a function of temperature we have determined the antiferromagnetic structure that coincides with the one obtained from density functional theory calculations. It is accompanied by anomalous asymmetric distortions of the CrO_{6} octahedra. Strong coupling and Lanczos calculations on a derived Kugel-Khomskii Hamiltonian yield a simultaneous orbital and moment ordering. Our results favor an exotic ordered phase of orbital singlets not originated by frustration.
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We study a model proposed before to give rise to a nonconventional pairing mechanism in BaPb[sub 1[minus][ital x]]Bi[sub [ital x]]O[sub 3] and Ba[sub 1[minus][ital x]]K[sub [ital x]]BiO[sub 3]. This model, in which both phonons and... more
We study a model proposed before to give rise to a nonconventional pairing mechanism in BaPb[sub 1[minus][ital x]]Bi[sub [ital x]]O[sub 3] and Ba[sub 1[minus][ital x]]K[sub [ital x]]BiO[sub 3]. This model, in which both phonons and electronic excitations play an essential role, is supported by experimental evidence. We solve exactly a BiO[sub 6] cluster and we calculate the interaction between this
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Page 1. PHYSICAL REVIEW B VOLUME 51,NUMBER 20 15 MAY 1995-II Single-particle spectral function of a generalized Hubbard model: Metal-insulator transition E. R. Gagliano, AA Aligia, and Liliana Arrachea* Centro Atomico ...
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The BiO(m) high-Tc oxides are studied and compared to the CuO(n) systems (m, n = 2 or 3). Both are described by a general Hamiltonian and studied by perturbation theory in the hopping energy. It is shown that a common polarization... more
The BiO(m) high-Tc oxides are studied and compared to the CuO(n) systems (m, n = 2 or 3). Both are described by a general Hamiltonian and studied by perturbation theory in the hopping energy. It is shown that a common polarization mechanism can give rise to pairing of the O holes added to the antiferromagnetic or disproportionated semiconducting states. The necessary conditions are proximity of the M (Cu or Bi) and O levels, a gap in the electronic spectrum of the system, and important nearest-neighbor M-O repulsion.
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We calculate the electronic structure of BaPb1-xBixO3 within a simplified version of a model proposed before for the superconductivity, taking into account the local disproportionation of the Bi atoms in the coherent potential... more
We calculate the electronic structure of BaPb1-xBixO3 within a simplified version of a model proposed before for the superconductivity, taking into account the local disproportionation of the Bi atoms in the coherent potential approximation. Three different regimes are obtained as a function of the Bi concentration x: normal metal, metallic with a pseudogap, and insulating phase. This allows a satisfactory
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ABSTRACT We study the effect of oxygen on magnetism at the (100) surface of Cr. Using the Hubbard Hamiltonian we find that chemisorbed oxygen strongly decreases the magnetic moments at the surface, while interstitially absorbed oxygen... more
ABSTRACT We study the effect of oxygen on magnetism at the (100) surface of Cr. Using the Hubbard Hamiltonian we find that chemisorbed oxygen strongly decreases the magnetic moments at the surface, while interstitially absorbed oxygen increases the magnetic moments. The resultant change of the magnetic-ordering temperature is estimated by application of a Heisenberg model. The results obtained agree qualitatively with recent experiments.