Thermal conductivity and specific heat of the linear chain cuprateSr2CuO3: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 ${\mathrm{Sr}}_2{\mathrm{CuO}}_3$ at low temperatures. In addition to a nearly isotropic phonon heat transport, we find a quasi-one-dimensional excess thermal conductivity along the chain direction, most likely associated with spin excitations (spinons). The spinon energy current is limited mainly by scattering on defects and phonons. Analyzing the specific heat data, the intrachain magnetic exchange ${J/k}_B$ is estimated to be $\simeq 2650\hspace{0.5em}\mathrm{K}.$