Comparison of physical properties for carbon nanotube doped MgB2 superconductors synthesized with different process

Abstract Carbon nanotubes (CNT) doping of magnesium diboride with a nominal stoichiometry of MgB 1.9 C 0.1 synthesized under ambient pressure (AP) and high pressure (HP) leads to an improvement in the critical current density J c and the upper critical field H c2 ( T ) with a slight depression in the superconducting transition temperature. The anomalous temperature dependence of H c2 ( T ) with a positive curvature implies the existence of two gaps in both samples. At elevated fields, the fact of the current density decays as J c ( H ) ∝  H − β in HP samples suggests a possible route to overcome J c ( H ) decreasing rapidly with increasing fields.