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, κ_c, 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 κ_c around 50 K, where large contribution of the thermal conductivity due to spinons, κ_spinon, is observed, is markedly enhanced by both the increase of the purity of raw materials and the O₂-annealing. Therefore, the increase of κ_c implies that κ_spinon 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 Å at low temperatures in the O₂-annealed single-crystal grown from raw materials with 4N purity.