Effect of plastic deformation of V,Nb and Ta on the superconducting transition temperature and the specific heat coefficients

Specific heat measurements performed between 1.4 and 20 K on bulk and cold-worked V, Nb and Ta superconducting materials are presented. The plastic deformation produces an increase in the superconducting transition temperature T_c, an increase which is relatively less important for Ta than for Nb and less for Nb than for V. An increase is registered for the normal linear coefficient of specific heat γ whereas the Debye temperature decreases slightly. The apparent relation between the increase of T_c and γ suggests qualitatively that the vibrating mobile dislocation contribution is not the only origin of the increase of γ but that a band structure contribution is also to be taken into account.