Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 16: Posters Correlated Electrons, Measuring Devices, Cryotechnique

TT 16.3: Poster

Samstag, 5. März 2005, 11:00–16:30, Poster TU C

Systematic Strong-Coupling Expansion of the T⊗t Jahn-Teller System — •Heinz Barentzen — Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart

Transition-metal oxides are notoriously difficult to describe because of a rather strong interplay between the spin, orbital and lattice degrees of freedom.This applies, in particular, to the recently investigated titanates with one t_2g electron per site, whose magnetic properties are surprising and controversial. Thus, e.g., while YTiO₃ shows a ferromagnetic ground state accompanied by a large Jahn-Teller (JT) distortion, LaTiO₃ exhibits an antiferromagnetic ground state with no detectable JT effect. To resolve the puzzling magnetic behavior of LaTiO₃, the concept of an orbital liquid has been worked out by Khaliullin et al.(Phys. Rev. Lett. 85, 3950 (2000)), while a perturbing crystal field of the GdFeO₃-type has been proposed by Mochizuki and Imada (J. Phys.Soc.Jpn. 70, 2872 (2001)).

To put these concepts on a quantitative basis we intend to elucidate the role of the T⊗t JT problem, relevant to these systems. So far, however, analytic results are available only for the limiting cases of weak and strong coupling. In an attempt to find the lowest eigenvalue of the T⊗t system over the whole coupling range, we have recently succeeded in obtaining systematic expansions for weak and strong coupling, the first steps on the way towards the complete solution of the problem. The reasoning behind these expansions will be explained and illustrated for the strong-coupling case.