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TT: Fachverband Tiefe Temperaturen

TT 3: Complex Oxides: Bulk Properties (joint session TT/HL/MA)

TT 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 e_g 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 t_2g compounds, however, the problem remains open. In these systems both the electron-lattice coupling and the hopping integrals are typically smaller than those for e_g compounds; on the other hand, orbital degeneracy is larger, which enhances the effects of super-exchange. Here we investigate representative t_2g¹ 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.

[1] E. Pavarini, E. Koch and A. I. Lichtenstein, Phys. Rev. Lett. 101, 266405 (2008).

[2] E. Pavarini and E. Koch, Phys. Rev. Lett. 104, 086402 (2010).