Pressure dependence of the superconducting transition temperature for vanadium

The superconducting transition temperature T c , for vanadium has been determined as a function of hydrostatic pressure up to 24 kbar for a number of samples covering a wide range of resistance ratios. T c is observed to increase linearly for all of the samples at a rate (mean value 0.62+or-0.03*10 -5 K bar -1 ) which is almost independent of its initial value and which is considerably smaller than reported previously. The difference is attributed to the use of better hydrostatic pressure conditions in the author's investigation. The measured delta T c / delta P for V, Nb and Ta are shown to be thermodynamically consistent with measurements of the volume difference between the superconducting and normal states. These measured delta T c / delta P are also compared with the results of a recent theoretical calculation. The intrinsic T c for vanadium is estimated to be 5.46+or-0.02 K. The variation of the zero pressure T c values as a function of resistance ratio yields an energy gap anisotropy parameter (a 2 ) which is consistent with that obtained from direct measurements of the gap.