Excess conductivity in nano-carbon doped MgB2 superconductor Ebrahim Rostamabadi, Shaban Reza Ghorbani and Xiaolin Wang Eur. Phys. J. B, 92 5 (2019) 94 Published online: 08 May 2019 DOI: 10.1140/epjb/e2019-100063-8