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TT: Fachverband Tiefe Temperaturen

TT 40: Poster Session Correlated Electrons

TT 40.43: Poster

Mittwoch, 13. März 2013, 15:00–19:00, Poster D

Magnetic susceptibility measurements in the metal-organic spin-dimer system TK91 at very low temperatures — •S. Becker¹, U. Tutsch¹, B. Wolf¹, Y. Tsui¹, A. Brühl¹, T. Kretz², H.-W. Lerner², M. Wagner², S. Wessel³, T. Saha-Dasgupta⁴, H. Jeschke⁵, R. Valentí⁵, and M. Lang¹ — ¹Phys. Inst., Goethe-Universität, 60438 Frankfurt — ²Inst. f. Anorg. Chemie, Goethe-Universität, 60438 Frankfurt — ³Inst. f. Theor. Festkörperphysik, RWTH Aachen, 52056 Aachen — ⁴S.N. Bose National Centre for Basic Sciences, Salt Lake City, Kolkata 700098, India — ⁵Inst. f. Theor. Physik, Goethe-Universität, 60438 Frankfurt

Low-dimensional quantum spin systems show interesting properties at very low temperatures and sufficiently high magnetic fields. According to first principle Density Functional Theory calculations, the compound C₃₆H₄₈Cu₂F₆N₈O₁₂S₂ (TK91) is expected to be a 2-dimensionally (2d) coupled spin-1/2 dimer system with an intradimer interaction of J₁/k_B ∼ 10 K and interdimer couplings of J_i/k_B ∼ 1 K. We report on high-resolution ac-susceptibility measurements on TK91 as function of magnetic field B≤8 T and temperature 0.04 K≤ T≤1 K. Quantum Monte Carlo simulations for various interdimer coupling schemes fit the data very well for the 2d model whereas significant deviations are observed for all other cases thus confirming TK91 as a 2d spin-dimer system. In particular, we identify a range in the B-T phase diagram where the system shows distinct 2dXY behaviour accompanied by the formation of vortices and antivortices in the effective spin configuration.