Showing papers by "C. A. Balseiro published in 1988"
TL;DR: This work uses a cell approximation to show that the basic assumptions together with quasidegeneracy of p and d energies leads to attractiave interactions between holes in the ceramic superconductors.
Abstract: We study the electronic structure of Cu-O high-${T}_{c}$ superconductors using a tight-binding Hamiltonian with strong intra-atomic and interatomic Coulomb repulsion. We assume that only $\mathrm{Cu}({3d}_{{x}^{2}\ensuremath{-}{y}^{2}})$ and $\mathrm{O}({2p}_{x})$ and $\mathrm{O}({2p}_{y})$ orbitals are relevant. We solve finite clusters exactly and use a cell approximation to show that the basic assumptions together with quasidegeneracy of $p$ and $d$ energies leads to attractive interactions between holes in the ceramic superconductors.
29 citations
TL;DR: In this article, a simple numerical approach to compute dynamic correlation functions in quantum many-body systems at zero temperature is presented, based on a projective technique for the memory function formalism, and requires as a starting point an independent evaluation of the ground-state energy and wave function.
Abstract: We present a simple numerical approach to compute dynamic correlation functions in quantum many-body systems at zero temperature. The method is based on a projective technique for the memory-function formalism, and requires as a starting point an independent evaluation of the ground-state energy and wave function. We illustrate the method with a one-dimensional model of spinless fermions and calculate the density-density, current-current, and single-particle correlation functions. The obtained spectral functions show different types of elementary excitations: particle-hole, soliton-antisoliton, exciton, etc. We compare our results with analytical results, and with those obtained through different approaches available in the literature.
21 citations
5 citations
TL;DR: In this article, the neutral-to-ionic transition in organic charge-transfer compounds in finite-size stacks was studied, and the stability of both phases against dimerization was shown to depend on the value of the rigidity of the stack.
Abstract: We have studied the neutral-to-ionic transition in organic charge-transfer compounds in finite-size stacks. To describe these systems we use a model that includes (i) infinite intramolecular Coulomb repulsion, (ii) hybridization between nearest-neighbor molecules (t), and (iii) nearest-neighbor electron-hole attraction (G). Through a recently developed modified Lanczos method we obtain exact numerical results for the following physical quantities: (i) ground-state energy, (ii) occupation of acceptor molecules, (iii) a gap between the ground and first excited state, (iv) a gap between the ground and first triplet excited state, (v) charge-charge and spin-spin correlation functions, and (vi) neutral-ionic parameter phase diagram. The neutral-ionic phase transition is continuous for small G/t and abruptly discontinuous for large G/t, the crossover occurring around G/t\ensuremath{\sim}2. We also study the stability of both phases against dimerization and find that within the model the ionic phase is always unstable against this distortion, while the stability of the neutral phase depends on the value of the rigidity of the stack. We offer a strong-coupling argument that explains this result.
3 citations
TL;DR: The precise mechanism which allows the hybridization between nearly degenerate localized 4f and (6s,5d)-conduction-band states of a mixed-valent rare earth (RE) is investigated in detail and a dynamic symmetry breaking is proposed.
Abstract: The precise mechanism which allows the hybridization between nearly degenerate localized 4f and (6s,5d)-conduction-band states of a mixed-valent rare earth (RE) is investigated in detail We propose that a dynamic symmetry breaking, generated by coupling the displacement of the RE ion from its equilibrium position to the mixing term of the Anderson Hamiltonian, induces the hybridization of the opposite-parity f and sd states The model is solved under the assumption that the degeneracy of the 4f level, N/sub f/, is large, which yields exact results in the N/sub f/-->infinity limit Also, only one Einstein phonon mode is retained Both a semiclassical and a full quantum-mechanical treatment are presented Finally, we apply our model to the metal-insulator transition of SmS
3 citations
TL;DR: In this article, a possible interpretation based on the CDW interaction with some internal degree of freedom associated with the pinning centers is proposed, which leads to deformed Shapiro steps as experimentally observed.
1 citations
TL;DR: In this article, the authors studied the charge distribution in GaAs−Ga1−xAlxAs heterostructures under an external magnetic field perpendicular to the interfaces, and they obtained the charge density profile by solving in a selfconsistent way the Poisson and Schrodinger equations.
Abstract: We study the charge distribution in GaAs‐Ga1−xAlxAs heterostructures under an external magnetic field perpendicular to the interfaces. We obtain the charge‐density profile by solving in a self‐consistent way the Poisson and Schrodinger equations. Our results show that in a quantum well of Ga1−xAlxAs‐GaAs‐Ga1−xAlxAs with widths ranging between 70 and 110 A the charge accumulation is a strongly dependent function of the well width and the external magnetic field.
1 citations
TL;DR: By studying the electronic structure of Cu-O planes in the strong correlation limit, the authors showed that the interatomic repulsion between Copper and Oxygen holes leads naturally to an attractive interaction between quasi-particles in these systems.
Abstract: By studying the electronic structure of Cu-O planes in the strong correlation limit we show that the interatomic repulsion between Copper and Oxygen holes leads naturally to an attractive interaction between quasi-particles in these systems. We present different numerical and analytic results to explore the parameter space where this mechanism is most favorable.
1 citations
TL;DR: In this article, the authors model the Cu-O high Tc compounds by a generalized Hubbard Hamiltonian that includes an intersite Coulomb repulsion G and use a real space renormalization group approach to calculate effective interactions and gap energies in infinite chains.
Abstract: We model the Cu-O high Tc compounds by a generalized Hubbard Hamiltonian that includes an intersite Coulomb repulsion G. We use a real space renormalization group approach to calculate effective interactions and gap energies in infinite chains. The results indicate attraction between added holes in these systems. The magnitudes of these attractive energies are compared with exact results obtained by the Lanczos method for finite clusters.
1 citations
TL;DR: In this article, it was shown that in a simple model which includes Cu3d and O 2p orbitals together with inter and intra atomic correlations pairing between holes can occur due to charge transfer excitations.
Abstract: We present some numerical results to show that in a simple model which includes Cu3d and O 2p orbitals together with inter and intra atomic correlations pairing between holes can occur due to charge transfer excitations. We present also a simple approximation to derive an effective Hamiltonian containing an interaction between particles which is attractive for some values of the different microscopic parameters.
1 citations