Pinning mechanism in carbon nanotube doping of MgB 2 superconductor

Abstract

MgB 1.9C 0.1 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 J c( H) in each sample. In the view of two-gap superconductivity in these samples, δT c pinning (resulting from the spatial fluctuations of the transition temperature) is dominant in the AP sample, while in the HP sample, both δT c and δl pinning (due to the mean-free-path fluctuations) act together and their contributions vary with temperature. Besides the improvement of H c2(0), due to the different pinning mechanism, J c( 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 J c( H) under elevated fields.