Anomalous thermal conductivity of frustrated Heisenberg spin-chains and ladders

We study the thermal transport properties of several quantum spin chains and ladders. We find indications for a diverging thermal conductivity at finite temperatures for the models examined. The temperature at which the non-diverging prefactor \kappa^{(th)}(T) peaks is in general substantially lower than the temperature at which the corresponding specific heat c_V(T) is maximal. We show that this result of the microscopic approach leads to a substantial reduction for estimates of the magnetic mean-free path \lambda extracted by analyzing recent experiments, as compared to similar analyses by phenomenological theories.