Low temperature thermal conductivity of polysulfur nitride, (SN)x.
Measurements of the thermal conductivity (K) of (SN)x are reported for the temperature (T) range 0.88 K to 4 K in applied magnetic fields (H) up to 18 k0e. The superconducting transition temperature (Tc) in zero field for our sample was 0.28 K (midpoint of the resistive transition). Over the entire temperature range the main contribution to κ is from phonons. This contribution varies as κ α T3 below 0.2 K and changes smoothly to κ α T above 1 K. For T t 1.5 K, where the specific heat is known, the phonon mean free path obtained from K is on the order of the smallest sample dimension. At lower temperatures, the estimated phonon mean free path becomes larger than the smallest sample dimension. This effect is not yet explained. Below Tc, the normal electron contribution to K is identified by using H to quench the superconductivity. The observed effect is consistent with that expected from the Wiedemann-Franz law provided corrections are made for degradation of the sample electrical conductivity due to aging and fibers broken in handling. The material used in these experiments was provided by R. L. Greene and G. B. Street. This work was supported by National Science Foundation grants DMR 73-06712 and DMR 77-23577.[/p]