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TT: Fachverband Tiefe Temperaturen

TT 86: Correlated Electrons: Other Materials

TT 86.6: Vortrag

Donnerstag, 3. April 2014, 10:45–11:00, BEY 81

On the orbital-ordering transition in KCuF₃ — •Hunter Sims¹, Eva Pavarini², and Erik Koch¹ — ¹German Research School for Simulation Sciences, 52428 Jülich, Germany — ²Institute for Advanced Simulation, Forschungszentrum Jülich, 52428 Jülich, Germany

The Mott insulating perovskite KCuF₃ is considered the paradigmatic system with long-ranged orbital order and a cooperative Jahn-Teller distortion of the F-octahedra. This broken symmetry state is usually understood as the result of the destabilization of the symmetric structure due to crystal-field splitting (Jahn-Teller effect) or to super-exchange between the orbitals (Kugel-Khomskii mechanism), which leads to a gain in energy with increasing distortion. This is counteracted by the quadratic deformation energy of the lattice. In this picture it is expected that, as a consequence of the lattice entropy, the distortions will be gradually reduced with increasing temperature until they finally vanish at the ordering temperature T_c. Such a transition is, however, not found experimentally. We explain why.