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Dresden 2009 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 29: Correlated Electrons: Low-dimensional Systems - Materials 2

TT 29.14: Talk

Wednesday, March 25, 2009, 17:45–18:00, HSZ 301

Volborthite Cu3V2O7(OH)2·2H2O: Orbital ordering on a distorted kagome geometry — •Oleg Janson1, Johannes Richter2, and Helge Rosner11MPI CPfS Dresden, Germany — 2University of Magdeburg

The mineral volborthite Cu3V2O7(OH)2·2H2O has been recently claimed as a candidate for a real material realization of a spin-1/2 kagomé lattice. Despite the monoclinic distortion which allows non-frustrated magnetic couplings, experiments reveal the presence of frustration and no clear evidence for long-range order down to 50 mK. Here, we present a theoretical investigation of this interesting material. Based on DFT calculations, we estimate the relevant orbitals and couplings. Quite unusual for cuprates, we find different magnetically active orbitals for structurally different Cu(I) and Cu(II) atoms: while the latter has a hole in a x2y2 orbital (like in most cuprates), for Cu(I) the 3z2r2 is half-filled like in CuSb2O6. This has a dramatic influence on exchange integrals, which have been estimated using the LSDA+U approach. The magnetic degrees of freedom are mapped onto a Heisenberg model. We find that the orbital order leads to a picture of coupled frustrated chains rather than a kagomé model. For the proposed spin model we investigate the classical as well the quantum ground state. The possible influence of spin anisotropy and Dzyaloshinskii-Moriya interactions will be briefly discussed.
ZIH and IFW Dresden are acknowledged for support with computational resources.

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