Atomic Heats of Normal and Superconducting Vanadium

The atomic heats of vanadium, in the normal and superconducting states, have been determined from just above the transition temperature, T₂=5. 03^K, down to 1. 1^. After corrections to the 1948 temperature scale had been made, the normal state atomic heat could be represented by C₍=+ (125) ^4R (T{) }^3, with = (9. 260. 03) 10^-3 joule mole^-1 deg^-2 and =3385^K. The entropy difference, S₍-Sₒ, between the normal and superconducting states, extrapolated to 0^, was found to vanish, in accordance with the third law of thermodynamics. The critical field values deduced from S₍-Sₒ gave H₀=1310 oersteds; at higher temperatures they were in agreement with initial penetration fields previously reported. The most interesting result of this work was that below about 0. 7T₂ the electronic contribution to the atomic heat of the metal in the superconducting state could be represented by an exponential expression of the form C₄ₒ{T₂}=ae^-b{T₂T} with a=9. 17 and b=1. 50; such an exponential relation is consistent with a single-electron model of a superconductor involving a gap of the order of kT₂ per electron in the spectrum of available energy levels.