1,721,104 research outputs found
Hall coefficient and angle-resolved photoemission in systems with strong pair fluctuations
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Local dynamical lattice instabilities: Prerequisites for resonant pairing superconductivity
Full text linkFluctuating local diamagnetic pairs of electrons, embedded in a Fermi sea, are candidates for non-phononmediated superconductors without the stringent conditions on Tc which arise in phonon-mediated BCS classical low-Tc superconductors. The local accumulations of charge, from which such diamagnetic fluctuations originate, are irrevocably coupled to local dynamical lattice instabilities and form composite charge-lattice excitations of the system. For a superconducting phase to be realized, such excitations must be itinerant spatially phase-coherent modes. This can be achieved by resonant pair tunneling in and out of polaronic cation-ligand sites. Materials in which superconductivity driven by such local lattice instability can be expected have a Tc which is controlled by the phase stiffness rather than the amplitude of the diamagnetic pair fluctuations. Above Tc, a pseudogap phase will be maintained up to T*, at which this pairing amplitude disappears. We discuss the characteristic local charge and lattice properties which characterize this pseudogap phase and which form the prerequisites for establishing a phase-coherent macroscopic superconducting state
Rotationally invariant parametrization of Coulomb interactions in multi-orbital Hubbard models
No full textMulti-orbital models with strong Coulomb correlations represent a fundamental tool for the analysis of transition metal oxides, which exhibit physical properties strongly affected by the orbital degrees of freedom. In this context, specific relations between the local coupling constants must be imposed in order to preserve spin and charge rotational invariance. We present here an alternative route for the derivation of these relations, based on the use of a complete set of commuting operators which includes the pseudospin orbital operator and thus is particularly suited for the study of systems where phenomena of orbital ordering are known to play a major role. This approach is expected to be useful in investigations of multi-orbital Hubbard models analyzed within the framework of the dynamical mean field theory or in exact diagonalization studies on finite-size clusters
Exact solution of the extended Falicov-Kimball model in the limit of zero conduction bandwidth
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