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Regensburg 2007 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 2: Quantum-Critical Phenomena

TT 2.1: Talk

Monday, March 26, 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. Buechner11IFW-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.

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