Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 22: Low-dimensional Systems - Materials
TT 22.10: Vortrag
Donnerstag, 29. März 2007, 12:00–12:15, H18
The electronic structure of the quantum critical system Li2ZrCuO4 — •Miriam Schmitt1, Jiři Málek2,3, Stefan-Ludwig Drechsler2, and Helge Rosner1 — 1MPI CPfS Dresden — 2IFW Dresden — 3Institute of Physics, ASCR, Praha, Czech Republic
Quasi one-dimensional magnetic chain compounds with nearest-neighbor
exchange J1 and next-nearest-neighbor exchange J2 exhibit a
quantum critical point (QCP) for the ratio J2/J1 = -0.25. The
recently synthesized compound Li2ZrCuO4, which contains spin-1/2
chains of distorted, edge shared CuO4 plaquettes, is close to this
QCP and shows therefore a strong field dependence of the thermodynamical
properties. From fits to the measured susceptibility and specific
heat, a ratio J2/J1 ∼ -0.3 was determined.[1] Here, we present a
detailed study of the electronic and magnetic properties of
Li2ZrCuO4 based on density functional calculations. We combine
results of LDA calculation, which were mapped onto an effective
one-band tight-binding model and subsequently to an extended
Heisenberg model with exchange integrals derived from total energy
differences for constraint magnetic states using LDA+U. The influence
of (i) the deviation from the standard, planar CuO4 geometry and
(ii) the experimentally observed Li disorder was carefully
investigated. We find J2/J1 ∼ −0.25 ± 0.03 very close to the
QCP. In addition, we obtain a sizeable inter-chain coupling J⊥∼ 7K playing an important role for the
saturation field due to the vicinity of the QCP.
The Emmy-Noether program is acknowledged for
financial support.
[1] S.-L. Drechsler et al. Phys. Rev. Lett., accepted.