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In fifth-group element superconductors V, Nb, and Ta, the increase in superconducting transition temperature (T c) was attempted by using both high-pressure torsion (HPT) and additional hydrostatic pressure (HP) compression. The former brings about the grain refinement and strain accumulation in the unit-cell level. The additional compression for severely strained superconductors triggers strengthening intergrain-contact and/or structural deformation in the unit-cell level. The manner of the appearance of the above two effects depends on the kind of elements: First, in V, there is no prominent effect of HPT, comparing to the hydrostatic compression effects on its non-strained material. Next, in Ta, the effect of strengthening intergrain-contact appears at small hydrostatic compression, resulting in temporal increase in T c. Finally, Nb exhibits prominent increase in T c by both effects and, in particular, the structural deformation in the unit-cell level promotes the increase in T c. Thus, the accumulation of residual strain in the level of starting material can be a promising work to manipulate T c under HP compression.

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It has been well known that the stability of the superconducting state against thermal fluctuation can be manipulated by applying static strain such as that produced by either stretching or squashing. We have succeeded in manipulating the Meissner signal of a typical cuprate superconductor Bi2Sr2Ca2Cu3Ox (termed Bi2223) with a dynamical stress of 1 MHz frequency, generated by a piezoelectric device. The magnitude of the superconducting transition temperature (Tc) shift observed there exceeds one hundred times as much as those under static strain. We consider that the acoustic stress induces dynamic perturbation toward the lattice, resulting in the suppression of the formation of Cooper pairing.

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