Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 2: Symposium: High Magnetic Field Phenomena in Low Dimensional Magnets
TT 2.8: Vortrag
Montag, 25. Februar 2008, 12:45–13:00, H 0104
Diverging low-temperature thermal expansion of the spin-ladder system (C5H12N)2CuBr4 — •Thomas Lorenz1, Oliver Heyer1, Markus Garst2, Fabrizio Anfuso2, Achim Rosch2, Christian Rüegg3, and Karl Krämer4 — 1Institue of Physics II, University of Cologne, Germany — 2Institue of Theoretical Physics, University of Cologne, Germany — 3Centre for Nanotechnology and Dep. of Phys. and Astronomy, University College London, UK — 4Department of Chemistry and Biochemistry, University of Bern, Switzerland
The magnetic subsystem of piperidinium copper bromide (C5H12N)2CuBr4 represents a model system of an experimental realization of a two-leg spin-ladder Hamiltonian. Due to comparatively weak antiferromagnetic exchange couplings along the legs (≃ 12.9 K) and the rungs (≃ 3.6 K) of the ladders, two quantum phase transition are easily accessible in this compound: at Hc1≃ 6.8 T the gap closes and at Hc2≃ 13.9 T the field-polarized ferromagnetic state is reached. We present high-resolution measurements of the uniaxial thermal expansion and magnetostriction of (C5H12N)2CuBr4. For both quantities we observe pronounced anomalies arising from the pressure dependencies of the critical fields. The thermal expansion shows a very complex behavior with various sign changes and approaches a 1/√T divergence at the critical fields. All these low-temperature features are semi-quantitatively explained within a free fermion model; full quantitative agreement is obtained with Quantum Monte Carlo simulations.
Supported by the DFG through SFB 608.