  It has been shown that graphene doping is sufficient to lead to an
improvement in the critical current density - field performance (Jc(B)), with
little change in the transition temperature in MgB2. At 3.7 at% graphene doping
of MgB2 an optimal enhancement in Jc(B) was reached by a factor of 30 at 5 K
and 10 T, compared to the un-doped sample. The results suggested that effective
carbon substitutions by grapheme, 2D nature of grapheme and the strain effect
induced by difference thermal coefficient between single grapheme sheet and
MgB2 superconductor may play an important role in flux pinning enhancement.
