Critical field for superconductivity and low-temperature normal-state heat capacity of tungsten

We have measured the critical magnetic field for superconductivity in tungsten from 5.5 to 15 mK using a ?-ray anisotropy thermometer, and we have measured the heat capacity between 0.35 and 25 K. Analysis of the data givesHo=1.237 Oe for the 0 K critical field,Tc=16.0 mK for the critical temperature, ?=1.008 mJ/mole · K2 for the coefficient of the electronic heat capacity, and To=383 K for the 0 K Debye temperature. The measured values of the critical fieldHc are consistently higher than those reported by Black, Johnson, and Wheatley (BJW) on the CMN temperature scale, but the temperature dependence is similar. This discrepancy and the temperature dependence ofHc suggest that both sets ofHc data are affected by magnetic impurities. Use of the calorimetric ? value permits an improved test of the CMN temperature scale with the very-low-temperatureHc data obtained by BJW.