Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 24: Postersitzung III: Korrelierte Elektronen, ”Orbital Physics”
TT 24.44: Poster
Mittwoch, 10. März 2004, 14:30–19:00, Poster A
Dimerization versus Orbital Moment Ordering in the Mott insulator YVO3 — •Peter Horsch1, Giniyat Khaliullin1 und Andrzej M. Oles2 — 1Max-Planck-Institut f. Festkoerperforschung, D-70569 Stuttgart, Germany. — 2Smoluchowski Institute of Physics, PL-30059 Krakow, Poland.
We investigate the magnetic and orbital ordering within the spin-orbital model [1] for cubic vanadates using exact diagonalization in combination with mean-field theory [2]. Increasing Hund’s exchange JH triggers a crossover from the valence-bond orbital states to C-type antiferromagnetic (AF) phase, while a finite spin-orbit coupling induces the staggered component of magnetization which couples to the t2g orbital moments. Our results provide a qualitative explanation of the observed spin canting and large reduction of magnetization in the C-AF phase of YVO3 [3]. At finite temperature an orbital instability in the C-type antiferromagnetic phase induces modulation of magnetic exchange constants even in the absence of lattice distortions. This dimerization should be distinguished from a usual Peierls instability, as it emerges at finite temperatures (and vanishes at zero temperature) due to an interplay of quantum effects and thermal fluctuations, which open the way towards dimerized orbital- and spin-correlations. The calculated spin structure factor shows a magnon splitting at q→=(0,0,π/2) due to the orbital dimerization, similar to the spinwave dispersions measured by Ulrich et al.
[1] G. Khaliullin, P. Horsch, A.M. Oles, Phys. Rev. Lett. 86,3879 (2001).
[2] P. Horsch, G. Khaliullin, A.M. Oles, Phys. Rev. Lett. in print (2003).
[3] C. Ulrich et al., Phys. Rev. Lett. in print (2003).