Superconducting properties in bulk nanostructured niobium prepared by high-pressure torsion

• We have studied the effect of the grain refinement on the superconductivity in Nb.
• The bulk nanostructured Nb samples have been prepared by high-pressure torsion (HPT).
• The critical temperature Tc and the critical current density Jc increase after HPT.
• The enhancement of Tc is consistent with the size effect for nanoscale superconductors.
• The increase of Jc can be explained by the enhanced vortex pinning.

We have measured the magnetization M(T, H) and the resistivity ρ(T) in bulk nanostructured Nb prepared by high-pressure torsion (HPT) and studied the effect of the grain refinement on the superconducting properties. With increasing revolution numbers N of HPT, the critical temperature Tc and the critical current density Jc increase. The enhancement of Tc is consistent with the size effect for nanoscale superconductors. The increase of Jc can be explained by the enhanced vortex pinning due to the introduction of lattice defects such as dislocations and grain boundaries.