Dresden 2009 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 29: Correlated Electrons: Low-dimensional Systems - Materials 2
TT 29.9: Vortrag
Mittwoch, 25. März 2009, 16:15–16:30, HSZ 301
Thermodynamic studies on the proposed 2D spin-liquid state in κ-(ET)2Cu2(CN)3 — •Rudra Sekhar Manna1, Andreas Bruehl1, Mariano de Souza1, John A. Schlueter2, and Michael Lang1 — 1Physikalisches Institut, J.W. Goethe-Universitaet Frankfurt, SFB/TR49, D-60438 Frankfurt(M), Germany — 2Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
The charge-transfer salt κ-(ET)2Cu2(CN)3, where ET = BEDT-TTF, is a spin S = 1/2 Mott insulator with a twodimensional (2D) triangular lattice structure. Because of the almost perfect geometrical frustration t/t ≈ 1 in this material, it has been proposed that quantum fluctuations destabilize long-range magnetic order and, instead, lead to liquid-like properties of the spin system [1]. Issues of high current interest include the nature of the low-lying elementary excitations of the spin liquid, particularly whether or not there is a spin gap, as well as the character of the anomaly observed around 6 K. The latter has been attributed to some "crossover" or "hidden order" [2]. Here we report on high-resolution thermal expansion and specific heat measurements focusing on the mysterious 6 K anomaly. We observe that this anomaly is accompanied by distinct and sharp features in the uniaxial-expansion coefficients suggestive of a second-order phase transition rather than a crossover. The data reveal a pronounced in-plane anisotropy corresponding to a significant distortion of the isotropic triangular lattice.
[1] Shimizu et al., Phys. Rev. Lett. 91, 107001 (2003).
[2] Yamashita et al., Nature Phys. 4, 459 (2008).