Linear temperature dependence of the magnetic heat conductivity in CaCu2O3.

We present experimental results for the thermal conductivity kappa of the pseudo-two-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 kappa mag along the chain direction. kappa mag is linear in temperature, resembling the low-temperature limit of the thermal Drude weight D th of the S=1/2 Heisenberg chain. The comparison of kappamag and Dth yields a magnetic mean-free path of l mag approximately 22+/-5 A, in good agreement with magnetic measurements.