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TT: Fachverband Tiefe Temperaturen
TT 45: Correlated Electrons: Poster Session
TT 45.63: Poster
Donnerstag, 29. März 2012, 15:00–19:00, Poster B
Thermal conductivity of the S = 1/2 two-leg spin-ladder compound bis(2,3-dimethylpyridinium) tetrabromocuprate (DIMPY) — •Gerhard Kolland1, Johannes Engelmayer1, Mark M. Turnbull2, and Thomas Lorenz1 — 1II. Physikalisches Institut, Universität zu Köln, Germany — 2Carlson School of Chemistry and Department of Physics, Clark University, Worcester, Massachusetts, USA
Bis(2,3-dimethylpyridinium) tetrabromocuprate (DIMPY) is a model material for a Heisenberg S=1/2 two-leg spin-ladder with antiferromagnetic couplings Jrung ≃ 4.3 K (along the rungs of the spin-ladder) and Jleg ≃ 8.4 K (along the legs) in the strong-leg regime, i.e. Jleg > Jrung. In zero magnetic field, the spin ladder has a finite excitation gap, which is closed at a lower critical field BC 1 ≃ 3 T, where the system enters a gapless Luttinger-liquid (LL) phase. At the saturation field BC 2 ≃ 30 T the system leaves the LL phase and a gap opens. We present measurements of the magnetic-field dependent thermal conductivity κ. The field was applied along the b direction. To investigate a magnetic contribution to κ, we measured the thermal conductivity parallel κ|| and perpendicular κ⊥ to the ladder direction. At higher temperatures around 2 K, the magnetic-field influence is rather similar for both directions. We observe a broad minimum around 5 T, which sharpens and approaches BC 1 with decreasing temperature. In addition, the magnetic-field dependent thermal conductivity gets anisotropic. Below 1 K, κ|| is strongly enhanced, whereas κ⊥ stays almost constant. Supported by the DFG through SFB 608.