Low-energy kink in the nodal dispersion of copper-oxide superconductors: Insights from Dynamical Mean Field Theory

Motivated by the observation in copper-oxide high-temperature superconductors, we investigate the appearance of kinks in the electronic dispersion due to coupling to phonons for a system with strong electronic repulsion. We study a Hubbard model supplemented by an electron-phonon coupling of Holstein type within Dynamical Mean Field Theory (DMFT) utilizing Numerical Renormalization Group as impurity solver. Paramagnetic DMFT solutions in the presence of large repulsion show a kink only for large values of the electron-phonon coupling $\lambda$ or large doping and, contrary to the conventional electron-phonon theory, the position of such a kink can be shifted to energies larger than the renormalized phonon frequency $\omega_0^r$. When including antiferromagnetic correlations we find a stronger effect of the electron-phonon interaction on the electronic dispersion due to a cooperative effect and a visible kink at $\omega_0^r$, even for smaller $\lambda$. Our results provide a scenario of a kink position increasing with doping, which could be related to recent photoemission experiments on Bi-based cuprates.Comment: 10 pages, 10 figures; additional referene

The electron-phonon interaction in strongly correlated electron systems

Francesco Guerra, Roberto Raimondi, Renzo Rose

Relevance of phonon dynamics in strongly correlated systems coupled to phonons: A Dynamical Mean Field Theory analysis

The properties of the electron-phonon interaction in the presence of a sizable electronic repulsion at finite doping are studied by investigating the metallic phase of the Hubbard-Holstein model with Dynamical Mean Field Theory. Analyzing the quasiparticle weight at finite doping, we find that a large Coulomb repulsion reduces the effect of electron-phonon coupling at low-energy, while this reduction is not present at high energy. The renormalization of the electron-phonon coupling induced by the Hubbard repul sion depends in a surprisingly strong and non-trivial way on the phonon frequency. Our results suggest that phonon might affect differently high-energy and low-energy properties and this, together with the effect of phonon dynamics, should be carefully taken into account when the effects of the electron-phonon interaction in a strongly correlated system, like the superconducting cuprates, are discussed.Comment: 10 pages, 7 figures - revised version with minor change

Importance of d-p Coulomb interaction for high TC_C cuprates and other oxides

Current theoretical studies of electronic correlations in transition metal oxides typically only account for the local repulsion between d-electrons even if oxygen ligand p-states are an explicit part of the effective Hamiltonian. Interatomic interactions such as Upd between d- and (ligand) p-electrons, as well as the local interaction between p-electrons, are neglected. Often, the relative d-p orbital splitting has to be adjusted "ad hoc" on the basis of the experimental evidence. By applying the merger of local density approximation and dynamical mean field theory (LDA+DMFT) to the prototypical case of the 3-band Emery dp model for the cuprates, we demonstrate that, without any "ad hoc" adjustment of the orbital splitting, the charge transfer insulating state is stabilized by the interatomic interaction Upd. Our study hence shows how to improve realistic material calculations that explicitly include the p-orbitals.Comment: 17 pages, 6 figures, our study shows that U_pd is the physics behind previous ad-hoc shifts of the d-p level splittin

Pairing and polarization in systems with retarded interactions

In a system where a boson (e.g, a phonon) of finite frequency $\omega_0$ is coupled to electrons, two phenomena occur as the coupling is increased: electron pairing and polarization of the boson field. Within a path integral formalism and a Dynamical Mean-Field approach, we introduce {\it ad hoc} distribution function which allow us to pinpoint the two effects. When $\omega_0$ is smaller than the bandwidth $D$, pairing and polarization occur for fairly similar couplings for all considered temperatures. When $\omega_0 > D$, the two phenomena tend to coincide only for $T \gg \omega_0$, but are no longer tied for low temperatures so that a state of paired particles without finite polarization is stabilized.Comment: 4 pages, 2 figure