Effects of plastic deformation on the superconducting specific-heat transition of niobium

Abstract

Effects of plastic deformation on the normal, zero-field, and mixed-state specific heat of the type-II superconductor niobium were experimentally investigated. A high-resolution ac calorimetry technique was developed and used to study the effects of plastic deformation on the specific-heat superconducting transition in fields up to 2750 Oe. A method for the analysis of high-resolution specific-heat data near the superconducting transition is presented and used to determine κ variations (within a material) caused by plastic deformation. The effects of plastic deformation on the bulk superconducting transition temperature and width are also shown. Measurements of the zero-field specific heat show a systematic increase in width of the specific-heat transition with increasing deformation as well as a small increase in Tc. Both κ and the κ variation increase with increasing plastic deformation. The analysis method allows the specific-heat data of the mixed state to be decomposed in a way consistent with previously reported anisotropy data for niobium.