Interaction-induced enhancement of $g$-factor in graphene

We study the effect of electron interaction on the spin-splitting and the $g$-factor in graphene in perpendicular magnetic field using the Hartree and Hubbard approximations within the Thomas-Fermi model. We found that the $g$-factor is enhanced in comparison to its free electron value $g=2$ and oscillates as a function of the filling factor $\nu$ in the range $2\leq g^{\ast}\lesssim 4$ reaching maxima at even $\nu$ and minima at odd $\nu$. We outline the role of charged impurities in the substrate, which are shown to suppress the oscillations of the $g^{\ast}$-factor. This effect becomes especially pronounced with the increase of the impurity concentration, when the effective $g$-factor becomes independent of the filling factor reaching a value of $g^{\ast}\approx 2.3$. A relation to the recent experiment is discussed.