Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 8: Correlated Electrons: Spin Systems and Itinerant Magnets 1
TT 8.14: Vortrag
Montag, 25. Februar 2008, 17:45–18:00, H 0104
Field-dependent thermal transport in the Haldane chain compound NENP — •A. V. Sologubenko1, T. Lorenz1, J. A. Mydosh1, and M. M. Turnbull2 — 1II. Physikalisches Institut, Universität zu Köln, 50937 Köln, Germany — 2Carlson School of Chemistry and Department of Physics, Clark University, Worcester, MA 01610, USA
Properties of materials in the vicinity of quantum phase transitions have recently attracted considerable attention. Of particular interest are low-dimensional magnetic systems with transitions between various gapless and gapped states, induced by an external magnetic field. We present experiments on the magnetic field dependent thermal transport in the spin S=1 chain material Ni(C2H8N2)2NO2(ClO4) [NENP]. In NENP, the Haldane energy gap in the magnon excitation spectrum can be greatly reduced by applying an external magnetic field, but it remains finite at the critical field. The thermal conductivity is strongly affected by the field-induced changes in the magnon spectrum. It is possible to clearly distinguish the magnetic and the phononic contributions to the total heat conductivity and to successfully analyze the spin contribution in terms of a quasiparticle model. The mean free path of the spin excitations, evaluated from our data, is temperature-independent and large, which has important implications for the theory of transport in quantum spin systems.
Supported by the Deutsche Forschungsgemeinschaft through SFB 608.