Insulator to metal transition in LaMnO3

JAVIER D. FUHR; MICHEL AVIGNON; BLAS ALASCIO

Río de Janeiro, Brazil

Workshop; 8th Latin American Workshop on Magnetism, Magnetic Materials and their Applications (LAW3M 2007); 2007

   The recent observation of a insulator to metal transition (IMT) [1] in pure LaMnO3 at 32 GPa and room temperature, well above the Neel temperature (145 K) and bellow the Jahn-Teller transition temperature (780K), opens the way to a study of the role of the orbital degrees of freedom on the electronic structure in a stoichiometric material. In this paper we focus our attention in the orbital aspects of the insulator to metal transition. We use a model Hamiltonian for the effective eg orbitals in the compound that includes the hopping t, the on site Coulomb repulsion U, and the electron-lattice interaction g. In order to include in an appropriate way the strong correlations induced by the dominant e-e interactions we introduce auxiliary fields (Slave Bosons, SB) to the description of the low energy states. We use the O-Mn distance (d) dependence of t according to Harrison [2], and the pressure-d relation from the experimental data to describe the evolution of the electronic structure with pressure. Our results confirm and make transparent the conclusion reached in previous ab-initio calculations [3,4]: the inclusion of the Coulomb energy is necessary and constitute an important factor enhancing the orbital polarization in these compounds. [1] I. Loa et al, Phys. Rev. Lett. 87, 125501 (2001). [2] Harrison, W.A., “Electronic structure and the properties of solids : the physics of the chemical bond”, San Francisco , W.H. Freeman ,1980. [3] Wei-Guo Yin et al, Phys. Rev. Lett. 96, 116405 (2006). [4] A. Yamasaki et al, Phys. Rev. Lett. 96, 166401 (2006).