Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 29: Correlated Electrons: Low-dimensional Systems - Materials 2
TT 29.14: Vortrag
Mittwoch, 25. März 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 Rosner1 — 1MPI 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 x2−y2
orbital (like in most cuprates), for Cu(I) the 3z2−r2 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.