1,721,185 research outputs found
Interplay of strong correlation and Jahn-Teller effect in orbitally degenerate systems
No full textWe study the unconventional insulating state in A(4)C(60) by means of the dynamical mean-held theory. The interplay between the electron-electron correlation and the Jahn-Teller interaction determines the properties of these compounds. The system is a Mott-Jahn-Teller insulator. In that state, conduction between molecules is blocked by on-site Coulomb repulsion, magnetism is suppressed by intra-molecular Jahn-Teller effect, and important excitations (such as optical and spin gap) are found to be essentially intra-molecular. Experimental values of the optical and spin gaps are recovered by our calculations. RI Capone, Massimo/A-7762-200
Competition between d-wave superconductivity and antiferromagnetism in the two-dimensional Hubbard model
No full textWe study the competition of antiferromagnetism and d-wave superconductivity at zero temperature in the two-dimensional Hubbard model using cellular dynamical mean-field theory for a 2x2 plaquette, and solve the associated cluster impurity model at zero temperature by means of exact diagonalization. The interplay between the two phases depends strongly on the strength of the correlation. At strong coupling (U greater than or similar to 8t) the two phases do not mix, and a first-order transition takes place as a function of doping between two pure phases. At weak coupling (U less than or similar to 8t) the two order parameters coexist within the same solution in a range of doping and the system smoothly evolves from the antiferromagnet to the superconductor. When the transition between the superconducting and the antiferromagetic phases is of the first-order, it is accompanied by a phase separation. RI Capone, Massimo/A-7762-200
The effects of the electron-phonon interaction on a Mott insulator
No full textUsing the dynamical mean field theory we show that an electron - phonon interaction can revert the energetic balance between the metallic state and the Mott insulator in the density-driven metal-insulator transition at zero temperature. We present results for the Hubbard - Holstein model where the Mott ground state is found for sufficiently high values of the electron - phonon coupling but still not in the polaronic regime. (C) 2003 Elsevier B. V. All rights reserved. RI Capone, Massimo/A-7762-200
Genesis of Coexisting Itinerant and Localized Electrons in Iron Pnictides
No full textWe show how the general features of the electronic structure of the Fe-based high-Tc superconductors are a natural setting for a selective localization of the conduction electrons to arise. Slave-spin and dynamical mean-field calculations support this picture and allow for a comparison of the magnetic properties with experiments. RI Capone, Massimo/A-7762-2008; de' Medici, Luca/H-5071-201
Cellular-dynamical mean-field theory of the competition between antiferromagnetism and d-wave superconductivity in the two-dimensional Hubbard model
No full textCellular dynamical mean field theory is used to study the competition of antiferromagnetism and d-wave superconductivity at zero-temperature in the two-dimensional Hubbard model. The outcome strongly depends on the value of the interaction. At strong coupling (U >= 8t) a first-order transition takes place as a function of doping between pure antiferromagnet and pure superconductor. At weak-coupling instead (U <= 8t) the groundstate has both antiferromagnetic and d-wave long-range order, and the system smoothly evolves from one phase to the other. The first-order transition at large interactions is accompanied by a phase separation. (c) 2006 Elsevier B.V. All rights reserved. RI Capone, Massimo/A-7762-200
Electron-phonon interaction on bundled structures: Static and transport properties
No full textWe study the small-polaron problem of a single electron interacting with the lattice for the Holstein model in the adiabatic limit on a comb lattice hen the electron-phonon interaction acts only on the base sites. The ground state properties can be easily deduced from the ones of a linear chain with a appropriate rescaling of the coupling constant. On the other hand, the dynamical properties, that involve the complete spectrum of the system, present an "exotic" behavior. In the weak coupling limit the Drude weight (zero-frequency-conductivity) is enhanced with respect to its free-case value, contrary to the linear chain case, where for every finite value one has suppression of the Drude peak. More interestingly, the loss of coherent electron motion and the polaronic localization of the carrier occurs for different coupling values. Thus for intermediate coupling, a different phase appears with large kinetic energy and no coherent motion. RI Capone, Massimo/A-7762-200
Lattice approaches to dilute Fermi gases: Legacy of broken Galilean invariance
No full textIn the dilute limit, the properties of fermionic lattice models with short-range attractive interactions converge to those of a dilute Fermi gas in continuum space. We investigate this connection using mean-field theory, and we show that the existence of finite lattice spacing has consequences down to very small densities. In particular, we show that the reduced translational invariance associated with the lattice periodicity has a pivotal role in the finite-density corrections to the universal zero-density limit. For a parabolic dispersion with a sharp cutoff, we provide an analytical expression for the corrections, and we find that the unavoidable cutoff contributes at leading-order to the corrections to the relevant observables. In a generic lattice we find a universal power-law behavior n(1/3) which leads to significant corrections already for small densities. Our results place strong constraints on lattice extrapolations of dilute Fermi gas properties. RI Capone, Massimo/A-7762-200
Cluster dynamical mean-field methods for d-wave superconductors: Role of geometry
No full textWe compare the accuracy of two cluster extensions of dynamical mean-field theory in describing d-wave superconductors, using as a reference model a saddle-point t-J model which can be solved exactly in the thermodynamic limit and at the same time reasonably describes the properties of high-temperature superconductors. The two methods are cellular dynamical mean-field theory, which is based on a real-space perspective, and dynamical cluster approximation, which enforces a momentum-space picture by imposing periodic boundary conditions on the cluster, as opposed to the open boundary conditions of the first method. We consider the scaling of the methods for large cluster size, but we also focus on the behavior for small clusters, such as those accessible by means of present techniques, with particular emphasis on the geometrical structure, which is definitely a relevant issue in small clusters. RI Capone, Massimo/A-7762-200
Optical sum rule anomalies in the cuprates: Interplay between strong correlation and electronic band structure
No full textWe theoretically analyze some of the anomalies of the optical sum rules in the high-temperature superconductors. In particular, we address the particularly strong dependence on temperature of the sum rule in the normal state. Both electron-electron correlations and the presence of a Van Hove singularity have been shown to enhance such a dependence. Here, we consider both effects simultaneously by means of dynamical mean-field theory for a two-dimensional Hubbard model with realistic parameters for different cuprates, and we find that the two effects are not cooperative, as they appear to compete with one another in the region of parameters relevant for the experiments. RI Capone, Massimo/A-7762-200
Rotationally invariant slave bosons for strongly correlated superconductors
No full textWe extend the rotationally invariant formulation of the slave-boson method to superconducting states. This generalization, building on the recent work by Lechermann et al. [Phys. Rev. B 76, 155102 (2007)], allows to study superconductivity in strongly correlated systems. We apply the formalism to a specific case of strongly correlated superconductivity, as that found in a multiorbital Hubbard model for alkali-doped fullerides, where the superconducting pairing has phonic origin, yet it has been shown to be favored by strong correlation owing to the symmetry of the interaction. The method allows to treat on the same footing the strong correlation effects and the interorbital interactions driving superconductivity, and to capture the physics of strongly correlated superconductivity, in which the proximity to a Mott transition favors the superconducting phenomenon. RI Capone, Massimo/A-7762-200
- …
