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TT: Fachverband Tiefe Temperaturen

TT 19: CE: Metal-Insulator Transition 2

TT 19.5: Vortrag

Mittwoch, 24. März 2010, 10:30–10:45, H18

Origin of Jahn-Teller distortion and orbital-order in LaMnO₃ — •Eva Pavarini¹ and Erik Koch² — ¹IFF und IAS, Forschungszentrum Jülich — ²GRS, Jülich

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 1150 K and to reproduce the occupied orbital deduced from neutron scattering.