Berlin 2012 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 40: Correlated Electrons: Low-dimensional Systems - Materials 3

TT 40.1: Vortrag

Donnerstag, 29. März 2012, 15:00–15:15, H 0104

Large quantum fluctuations in the strongly coupled spin-1/2 chains of green dioptase: a magic message from birds and trees — Oleg Janson, Alexander Tsirlin, Miriam Schmitt, and •Helge Rosner — Max-Planck-Institut für Chemische Physik fester Stoffe

We present a microscopic magnetic model for the natural mineral (green) dioptase Cu₆Si₆O₁₈·6H₂O. Based on full-potential DFT calculations, we find two relevant exchange couplings in this compound: an antiferromagnetic coupling J_c, forming spiral chains along the hexagonal axis, and a ferromagnetic interchain coupling J_d within the structural Cu₂O₆ dimers. To corroborate the proposed spin model, we perform quantum Monte-Carlo simulations for the dioptase spin lattice. The evaluated ground-state (the propagation vector and the sublattice magnetization) and thermodynamic properties [χ(T)] are in remarkably good agreement with the experimental data. The refined model parameters are J_c = 78 K and J_d = −37 K with J_d/J_c ≃ −0.5 [1]. Despite the lack of frustration and the 3D nature of the spin lattice, the low coordination number of 3 suffices to cause strong quantum fluctuations, as evidenced by the experiments. Alterations of the J_c–J_d model in closely related compounds will be briefly discussed.

[1] O. Janson, A. A. Tsirlin, M. Schmitt, and H. Rosner, Phys. Rev. B 82, 014424 (2010); arXiv:1004.3765.