  The particle effective mass in graphene is a challenging concept because the
commonly used theoretical expression is mathematically divergent. In this
paper, we use basic principles to present a simple theoretical expression for
the effective mass that is suitable for both parabolic and non-parabolic
isotropic materials. We demonstrate that this definition is consistent with the
definition of the cyclotron effective mass, which is one of the common methods
for effective mass measurement in solid state materials. We apply the proposed
theoretical definition to graphene and demonstrate linear dependence of the
effective mass on momentum, as confirmed by experimental cyclotron resonance
measurements. Therefore, the proposed definition of the effective mass can be
used for non-parabolic materials such as graphene.
