Indirect electron-phonon interaction leading to significant reduction of thermal conductivity in graphene

We investigate the effect of electron-phonon interaction (EPI) on the lattice thermal conductivity κph of graphene from first-principles calculations. By employing an iterative solution of Boltzmann transport equation (BTE), we highlight the marked effect of the indirect coupling between the flexural acoustic (ZA) phonons and electrons on the thermal conductivity in graphene. Although the ZA phonons, the dominant carriers of κph, do not interact with electrons directly due to the reflection symmetry with respect to the basal plane, their anharmonic interactions with the in-plane transverse acoustic (TA) and longitudinal acoustic (LA) phonons that can be effectively scattered by electrons have a significant effect on κph. This is originated from the dominance of normal processes over Umklapp processes in graphene. Specifically, this indirect effect can result in up to 21% reduction of κph even at room temperature, and 32% reduction in κph at 200 K. Moreover, κph does not decrease monotonically with increasing charge carrier density n. Instead, κph is minimized at ∼ 4.9×1014cm−2. This unusual finding is found to be strongly correlated with the electron density of states at corresponding Fermi levels. This indirect effect should also exist widely in other materials, whose intrinsic lattice thermal conductivities are dominated by normal processes. On the other hand, we also explore the electronic thermal conductivity κe varying with n. Intriguingly, at room temperature κe starts increasing dramatically at n=4.9×1014cm−2, where the corresponding Bloch-Grüneisen transition temperature ΘBG exceeds the room temperature.