Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 2: Quantum-Critical Phenomena
TT 2.1: Vortrag
Montag, 26. März 2007, 09:30–09:45, H19
The ’via cuprata’ from antiferromagnetic to ferromagnetic Heisenberg chains and Li2ZrCuO4 as a missing link near the quantum critical point — •S.-L. Drechsler1, J. Richter2, J. Malek1,3, M. Schmitt4, H. Rosner4, N. Tristan1, O. Volkova5, A. Vasiliev5, and B. Buechner1 — 1IFW-Dresden, PF 270116, D-01171 Dresden — 2Universität Magdeburg — 3Institute of Physics, ASCR, Praha, Czech Rep. — 4MPI CPfS Dresden — 5Lomonosov-University, Moscow, Russia
We consider 9 magnetic chain cuprates with ferromagnetic
nearest neighbor
exchange J1 and antiferromagnetic next-nearest neighbor exchange J2 from the vicinity of the
quantum critical point (QCP) for
αc=−J2/J1 = 0.25 up to 10.
Approaching αc the maximum position Tm of the magnetic susceptibility χ(T) tends to 0,
whereas χ(Tm) monotonously increases.
The
recently synthesized Li2ZrCuO4, which
contains spin-1/2 chains of edge-shared CuO4 plaquettes,
is close to αc
and shows therefore a strong field dependence of the
thermodynamical
properties. Fitting χ(T) and the specific
heat, α ∼ 0.3 was found [1].
Here, we present also a microscopic consideration of the origin of
the relative large J1≈ -30meV
within the framework of
an appropriate five-band extended Hubbard model including
the ferromagnetic direct exchange Kpd as well as
the Hund’s rule coupling on O sites.
In addition, we found that the obtained sizeable interchain coupling dominates the saturation field
due to the vicinity of the QCP.
[1] S.-L. Drechsler et al. Phys. Rev. Lett. 98 (2007), accepted.