Coexistence of the δl and δTc flux pinning mechanisms in nano-Si-doped MgB2

The flux pinning mechanisms of nano-Si-doped MgB2 are reported in this work. The field dependence of the critical current density, Jc(B), was analyzed within the collective pinning model. We found that the mechanisms for both δl pinning, i.e., pinning associated with charge-carrier mean free path fluctuations, and δTc pinning, which is associated with spatial fluctuations of the transition temperature, coexist in the nano-Si-doped MgB2 samples, while Hc2 increases greatly with increasing nano-Si doping level. However, their contributions are strongly temperature dependent. The δl pinning is dominant at low temperatures, decreases with increasing temperature, and is suppressed completely at temperatures close to the critical temperature, Tc. However, the δTc pinning mechanism shows opposite trends.