Is Thermal Conductivity of Graphene Divergent and Higher Than Diamond?

The thermal conductivity of monolayer graphene is an outstanding challenge with no consensus reached on its exact value and length convergence so far. We consider four-phonon scattering, phonon renormalization, and an exact solution to phonon Boltzmann transport equation (BTE) from first principles. Using this computational formalism with unprecedented sampling grid, we show that when four-phonon scattering is included the thermal conductivity is convergent with system size at a room temperature value of 1300 W/(m$\cdot$K), which is lower than that of diamond. On the contrary, considering three-phonon scattering only yields divergence with size due to the momentum-conserving normal processes of flexural phonons.