Dresden 2020 – wissenschaftliches Programm
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MA 3.8: Vortrag
Montag, 16. März 2020, 11:30–11:45, HSZ 201
Origin of orbital ordering in LaTiO3 and YTiO3 — •Xuejing Zhang and Eva Pavarini — Institute for Advanced Simulation, Forschungszentrum Jülich, D-52425 Jülich, Germany
The origin of orbital ordering (OO) in correlated oxides is strongly debated. Two main mechanisms have been proposed as possible explanation for OO phenomena. The first is the classical Jahn-Teller effect and the second is the electronic super-exchange, introduced by Kugel-Khomskii. In the case of the paradigmatic eg systems KCuF3 and LaMnO3 it has been shown that the electronic Kugel-Khomskii mechanism is not sufficient to drive the OO transition alone, at the temperatures at which orbitally order is typically observed by the co-operative Jahn-Teller distortion.[1,2] In the case of t2g compounds, however, the problem remains open. In these systems both the electron-lattice coupling and the hopping integrals are typically smaller than those for eg compounds; on the other hand, orbital degeneracy is larger, which enhances the effects of super-exchange. Here we investigate representative t2g1 systems in which OO is observed, the Mott insulators LaTiO3 and YTiO3. We show that the Kugel-Khomskii transition temperature is about 390 K, comparable to the one of KCuF3. This shows that static distortions are needed to explain the presence of OO at high temperature.
 E. Pavarini, E. Koch and A. I. Lichtenstein, Phys. Rev. Lett. 101, 266405 (2008).
 E. Pavarini and E. Koch, Phys. Rev. Lett. 104, 086402 (2010).