arXiv subjects

Roland Zeyher

Publications and source records attributed to Roland Zeyher.

21 records · Page 2Linked to original sources

arXiv1998

Jahn-Teller distortion and electronic correlation effects in undoped manganese perovskites

The formation of a long-range Jahn-Teller distortion in undoped manganites is studied within the dynamical mean-field theory taking both electron-phonon and electron-electron interactions into account. We find that the observed insulating behavior at temperatures above the Jahn-Teller transition and the bond-length changes below it can most naturally by explained by assuming a strong electronic repulsion and a rather weak electron-phonon coupling.

cond-mat.str-el↗

arXiv1998

Holstein model in infinite dimensions at half-filling

The normal state of the Holstein model is studied at half-filling in infinite dimensions and in the adiabatic regime. The dynamical mean-field equations are solved using perturbation expansions around the extremal paths of the effective action for the atoms. We find that the Migdal-Eliashberg expansion breaks down in the metallic state if the electron-phonon coupling $λ$ exceeds a value of about 1.3 in spite of the fact that the formal expansion parameter $λω_0/E_F$ ($ω_0$ is the phonon frequency, $E_F$ the Fermi energy) is much smaller than 1. The breakdown is due to the appearance of more than one extremal path of the action. We present numerical results which illustrate in detail the evolution of the local Green's function, the self-energy and the effective atomic potential as a function of $λ$.

cond-mat.str-el↗

arXiv1996

Statics and dynamics of charge fluctuations in the t-J model

The equation for the charge vertex $γ$ of the $t-J$ model is derived and solved in leading order of an 1/N expansion, working directly in terms of Hubbard operators. Various quantities which depend crucially on $γ$ are then calculated, such as the life time and the transport life time of electrons due to a charge coupling to other degrees of freedom and the charge-charge correlation function. Our results show that the static screening of charges and the dynamics of charge fluctuations depend only weakly on $J$ and are mainly determined by the constraint of having no double occupancies of sites.

cond-mat↗