Variation of the Elastic Moduli at the Superconducting Transition

Using an ultrasonic technique capable of measuring changes in the elastic moduli as small as one part in 10
⁷
, the small modulus changes associated with the normal-to-superconducting transition have been measured as a function of both temperature and magnetic field. Single-crystal specimens of the cubic metals Pb, V, Nb and Ta were used and all their elastic moduli measured so that changes in the bulk modulus and Debye θ could be computed. The results showed that changes in the zero-point energy of the lattice can be far from negligible. Furthermore, the shear moduli are the most changed by the appearance of superconductivity.