The recent observation of a pressure-induced insulator to metal ($I\mathrm{\text{−}}M$) transition in pure ${\mathrm{LaMnO}}_3$ [I. Loa et al., Phys. Rev. Lett. 87, 125501 (2001).], opens the way to a study of the role of the orbital degrees of freedom on the electronic structure in a stoichiometric material and its interaction with lattice distortion. To obtain the energy of the system, we resort to a slave boson description for the electronic part and add an elastic term associated to the Jahn-Teller distortion. We obtain the evolution of the electronic structure and the Jahn-Teller distortion with pressure. We find that the Jahn-Teller distortion does not vanish before entering the metallic phase, that the gap closes with pressure in a way similar to that indicated by the temperature dependence of the conductivity, and that both Coulomb and Jahn-Teller interactions are necessary to describe appropriately the phase transition in ${\mathrm{LaMnO}}_3$.

• Received 24 October 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.216402