  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.

Strongly Correlated Electrons