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

Carbon nanotubes (CNT) doping of magnesium diboride with a nominal stoichiometry of MgB1.9C0.1 synthesized under ambient pressure (AP) and high pressure (HP) leads to an improvement in the critical current density Jc and the upper critical field Hc2(T) with a slight depression in the superconducting transition temperature. The anomalous temperature dependence of Hc2(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 Jc(H) ∝ H−β in HP samples suggests a possible route to overcome Jc(H) decreasing rapidly with increasing fields.