Enhancement of thermal conductivity due to spinons in the one-dimensional spin system SrCuO2

We have measured the thermal conductivity along the c-axis parallel to the spin-chains, κc, of the one-dimensional antiferromagnetic spin system SrCuO2, using as-grown and O2-annealed single-crystals grown from raw materials with 99.9 % (3N) and 99.99 % (4N) purity. The value of κc around 50 K, where large contribution of the thermal conductivity due to spinons, κspinon, is observed, is markedly enhanced by both the increase of the purity of raw materials and the O2-annealing. Therefore, the increase of κc implies that κspinon is enhanced due to the decrease of spin defects caused by impurities in raw materials and by oxygen defects. The mean free path of spinons is as large as about 24000 A at low temperatures in the O2-annealed single-crystal grown from raw materials with 4N purity.