  The design of graphene-based composite with high thermal conductivity
requires a comprehensive understanding of phonon coupling in graphene. We
extended the two-temperature model to coupled groups of phonon. The study give
new physical quantities, the phonon-phonon coupling factor and length, to
characterize the couplings quantitatively. Besides, our proposed coupling
length has an obvious dependence on system size. Our studies can not only
observe the nonequilibrium between different groups of phonon, but explain
theoretically the thermal resistance inside graphene.
