A kink in the transport of heat through graphene

When graphene is suspended over a cavity, it often adheres to the cavity’s sidewall resulting in sharp kinks in the graphene. This work shows that these kinks lead to unusual heat transport through graphene.  Heat transport happens due to the vibrations of atoms (phonons) in the graphene, which propagate through the sheet. These come in two flavors: the in-plane phonons which propagate very fast due to the stiff carbon-to-carbon bonds, and the out-of-plane phonons which propagate approximately 100 times slower.

Now when a kink occurs in the graphene, the slow out-of-plane phonons have to either continue as much faster in-plane phonons or reflect back. The large velocity difference makes it very difficult for these out-of-plane phonons to cross the kink, causing almost all of them to reflect. This results in a large thermal resistance and thus a temperature jump at the kink. This kink effect could explain recent experimental observations in graphene, where it was found that the graphene heats up much slower than expected.