Pinning mechanism in carbon nanotube doping of MgB2 superconductor

MgB1.9C0.1 samples are synthesized under the ambient pressure (AP) and high pressure (HP), respectively. The further studies demonstrate different field-dependence of the critical current density Jc(H) in each sample. In the view of two-gap superconductivity in these samples, δTc pinning (resulting from the spatial fluctuations of the transition temperature) is dominant in the AP sample, while in the HP sample, both δTc and δl pinning (due to the mean-free-path fluctuations) act together and their contributions vary with temperature. Besides the improvement of Hc2(0), due to the different pinning mechanism, Jc(H) of the HP sample shows a slower decay with the increasing fields than that of the AP sample in high fields, which suggests a possible method of retarding the rapid decay of Jc(H) under elevated fields.