Third-order nonlinearity of graphene: Effects of phenomenological relaxation and finite temperature

This article was published in Physical Review B, 91 (2015). An erratum to this article is available: J. L. Cheng, N. Vermeulen, and J. E. Sipe Phys. Rev. B 93, 039904 (http://dx.doi.org/10.1103/PhysRevB.93.039904)