Origin of Jahn-Teller distortion and orbital-order in LaMnO3

TL;DR

This paper investigates the origins of Jahn-Teller distortion and orbital order in LaMnO3, highlighting the roles of superexchange interactions, lattice distortions, and electron-phonon coupling in stabilizing these phenomena at high temperatures.

Contribution

The study combines density functional and dynamical mean-field calculations to disentangle superexchange and lattice effects, revealing electron-phonon coupling's crucial role in LaMnO3.

Findings

Superexchange alone predicts a transition temperature of 650 K.

Lattice distortions lower the transition temperature to 550 K.

Electron-phonon coupling explains Jahn-Teller distortions persisting above 1150 K.

Abstract

The origin of the cooperative Jahn-Teller distortion and orbital-order in LaMnO3 is central to the physics of the manganites. The question is complicated by the simultaneous presence of tetragonal and GdFeO3-type distortions and the strong Hund's rule coupling between e_g and t_2g electrons. To clarify the situation we calculate the transition temperature for the Kugel-Khomskii superexchange mechanism by using the local density approximation+dynamical mean-field method, and disentangle the effects of super-exchange from those of lattice distortions. We find that super-exchange alone would yield T_KK=650 K. The tetragonal and GdFeO3-type distortions, however, reduce T_KK to 550 K. Thus electron-phonon coupling is essential to explain the persistence of local Jahn-Teller distortions to at least 1150 K and to reproduce the occupied orbital deduced from neutron scattering.