We present experiments on the thermal transport in the spin-1/2 chain compound copper pyrazine dinitrate Cu(C_4 H_4 N_2)(NO_3)_2. The heat conductivity shows a surprisingly strong dependence on the applied magnetic field B, characterized at low temperatures by two main features. The first one appearing at low B is a characteristic dip located at mu_B B ~ k_B T, that may arise from Umklapp scattering. The second one is a plateau-like feature in the quantum critical regime, mu_B |B-B_c| < k_B T, where B_c is the saturation field at T=0. The latter feature clearly points towards a momentum and field independent mean free path of the spin excitations, contrary to theoretical expectations.
@article{arxiv.cond-mat/0612486,
title = {Magnetothermal transport in the spin-1/2 chains of copper pyrazine dinitrate},
author = {A. V. Sologubenko and K. Berggold and T. Lorenz and A. Rosch and E. Shimshoni and M. D. Phillips and M. M. Turnbull},
journal= {arXiv preprint arXiv:cond-mat/0612486},
year = {2007}
}