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TT: Fachverband Tiefe Temperaturen
TT 32: Correlated Electrons: Poster Session
TT 32.25: Poster
Thursday, February 28, 2008, 14:00–18:00, Poster B
Thermodynamics of Spin-Ladder and Spin-Chain Systems close to Quantum Criticality — •J. Rohrkamp1, T. Lorenz1, A. V. Sologubenko1, O. Heyer1, M. Garst2, F. Anfuso2, A. Rosch2, K. Krämer3, and M. M. Turnbull4 — 1II. Physikalisches Institut, Universität zu Köln — 2Institut für Theoretische Physik, Universität zu Köln — 3Department of Chemistry and Biochemistry, University of Bern — 4Carlson School of Chemistry and Department of Physics, Clark University
Compounds with magnetic subsystems representing simple model spin systems with weak magnetic coupling constants are ideal candidates to test theoretical predictions for the generic behavior close to quantum phase transitions. We present measurements of the thermal expansion, magnetostriction and thermal conductivity of the spin-1/2-ladder system piperidinium copper bromide (C5H12N)2CuBr4 and the spin-1/2-chain compound copper pyrazine dinitrate Cu(C4H4N2)(NO3)2. Both compounds show quantum phase transitions as a function of magnetic field with pressure dependent critical fields. The low-temperature thermal expansion approaches 1/√T divergences at the critical fields and shows a complex behavior with various sign changes inbetween.