Graphene Micro-Substrate Induced High Electron-Phonon Coupling in $\hbox {MgB}_{2}$

Electron-phonon coupling strength was studied in graphene-MgB₂ composites to explore the possibilities for a higher superconducting transition temperature (T_c). For the first time in the experimental work on MgB₂, the Raman active E_2g 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 T_c of graphene-MgB₂ composites because it increases the electron-phonon coupling strength of MgB₂.