Graphene micro-substrate induced high electron-phonon coupling in MgB2

Electron-phonon coupling strength was studied in graphene-MgB2 composites to explore the possibilities for a higher superconducting transition temperature (Tc). For the first time in the experimental work on MgB2, the Raman active E2g mode was split into two parts: a softened mode corresponding to tensile strain and a hardened mode attributed to the carbon substitution effect. The tensile strain effect is suggested to improve Tc of graphene-MgB2 composites because it increases the electron-phonon coupling strength of MgB2.