Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 18: Correlated Electrons: Low-dimensional Systems - Materials 2

TT 18.8: Talk

Tuesday, February 26, 2008, 17:15–17:30, H 2053

Thermal conductivity of TiOX (X=Br,Cl) — •Nikolai Hlubek¹, Christian Hess¹, Bernd Büchner¹, Michael Sing², Ralph Claessen², Sander van Smaalen³, and Paul van Loosdrecht⁴ — ¹IFW Dresden, Germany — ²Experimentelle Physik 4, Universität Würzburg, Germany — ³Laboratory of Crystallography, Universität Bayreuth, Germany — ⁴Zernike Institute for Advanced Materials, University of Groningen, Netherlands

We report experimental results on the thermal conductivity κ(T) of the compounds TiOBr and TiOCl. Below room temperature the compounds undergo two phase transitions T_c2 and T_c1. Above T_c2 the compounds should contain S=1/2 spin-chains with J_Cl=676K and J_Br=375K respectively formed by direct orbital overlap of the Ti-atoms. Below T_c1 the chains dimerise to form a non-magnetic ground state. Our data exhibits pronounced anomalies at T_c2 and T_c1 confirming the transitions being of second and first order respectively. Surprisingly, κ(T) appears to be dominated by phonon heat conduction, since we don’t find indications of significant magnetic contributions. This is in contrast to the expectation of a spin chain system. In this context we discuss possible scenarios to understand the unusual behaviour of the thermal conductivity.