Thermal conductivity and specific heat of the linear chain cuprate Sr2CuO3: Evidence for thermal transport via spinons

We report measurements of the specific heat and the thermal conductivity of the model Heisenberg spin-1/2 chain cuprate Sr2CuO3 at low temperatures. I n addition to a nearly isotropic phonon heat transport, we find a quasi-one -dimensional excess thermal conductivity along the chain direction, most li kely associated with spin excitations (spinons). The spinon energy current is limited mainly by scattering on defects and phonons. Analyzing the speci fic heat data, the intrachain magnetic exchange J/k(B) is estimated to be s imilar or equal to 2650 K.