Magnetic heat conductivity in CaCu₂O₃: linear temperature dependence

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We present experimental results for the thermal conductivity κ of the pseudo 2-leg ladder material CaCu₂O₃. The strong buckling of the ladder rungs renders this material a good approximation to a S=1/2 Heisenberg-chain. Despite a strong suppression of the thermal conductivity of this material in all crystal directions due to inherent disorder, we find a dominant magnetic contribution κₘag along the chain direction. κₘag is linear in temperature, resembling the low-temperature limit of the thermal Drude weight Dₜh of the S=1/2 Heisenberg chain. The comparison of κₘag and Dₜh yields a magnetic mean free path of lₘag≈ 22 ± 5 Å, in good agreement with magnetic measurements.