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Lower and upper Hubbard bands: A slave-boson treatment

2011-12-22T13:34:34Z

Lower and upper Hubbard bands: A slave-boson treatment Raimondi, Roberto; Castellani, Claudio 1993 Physical Review B 48 11453 - 11456 We analyze the single-particle spectral density and the optical conductivity of the single-band Hubbard model in the insulating Mott phase within the slave-boson technique. We show that the boson fluctuations around the saddle-point solution build up the lower and upper Hubbard bands and give rise to the optical conductivity which describes transitions between these incoherent bands. We find that the Brinkman-Rice metal-insulator transition is characterized by the simultaneous vanishing of the jump in the chemical potential, the single-particle spectral density gap, and the optical gap.

Nonlinear effects and dephasing in disordered electron systems

2011-12-22T13:34:34Z

Nonlinear effects and dephasing in disordered electron systems Raimondi, Roberto; Schwab, Peter; Castellani, Claudio 1999 Physical Review B 60 5818 - 5831 The calculation of the dephasing time in electron systems is presented. By means of the Keldysh formalism, we discuss in a unifying way both weak localization and interaction effects in disordered systems. This allows us to show how dephasing arises both in the particle-particle channel (weak localization) and in the particle-hole channel (interaction effect). First we discuss dephasing by an external field. Besides reviewing previous work on how an external oscillating field suppresses the weak localization correction, we derive a new expression for the effect of a field on the interaction correction. We find that the latter may be suppressed by a static electric field, in contrast to weak localization. We then consider dephasing due to inelastic scattering. The ambiguities involved in the definition of the dephasing time are clarified by directly comparing the diagrammatic approach with the path-integral approach. We show that different dephasing times appear in the particle-particle and particle-hole channels. Finally we comment on recent experiments.

Gutzwiller scheme for electrons and phonons: The half-filled Hubbard-Holstein model

2011-12-22T13:34:34Z

Gutzwiller scheme for electrons and phonons: The half-filled Hubbard-Holstein model Barone, Paolo; Raimondi, Roberto; Capone, Massimo; Castellani, Claudio; Fabrizio, Michele 2008-06-19T07:19:16Z Physical Review B 77 235115 We analyze the ground-state properties of strongly correlated electrons coupled with phonons by means of a generalized Gutzwiller wave function, which includes phononic degrees of freedom. We study in detail the paramagnetic half-filled Hubbard-Holstein model, where the electron-electron interaction can lead to a Mott transition and the electron-phonon coupling to a bipolaronic transition. We critically discuss the quality of the proposed wave function in describing the various transitions and crossovers that occur as a function of the parameters. Previous variational attempts are recovered as particular choices of the wave function, while keeping all the variational freedom allows to access regions of the phase diagram, otherwise inaccessible within previous variational approaches.

Extended Gutzwiller wavefunction for the Hubbard-Holstein model

2011-12-22T13:34:34Z

Extended Gutzwiller wavefunction for the Hubbard-Holstein model Barone, Paolo; Raimondi, Roberto; Capone, Massimo; Castellani, Claudio; Fabrizio, Michele 2007-07-20T08:20:21Z Europhysics Letters 79 47003 We introduce a new type of Gutzwiller variational wave function for correlated electrons coupled to phonons, able to treat on equal footing electronic and lattice degrees of freedom. We benchmark the wave function in the infinite-U Hubbard-Holstein model away from half-filling on a Bethe lattice, where we can directly compare with exact results by the Dynamical Mean-Field Theory. For this model, we find that variational results agree perfectly well with the exact ones. In particular the wave function correctly describes the crossover to a heavy polaron gas upon increasing the electron-phonon coupling.