Tuning the phonon transport in bilayer graphene to an anomalous regime dominated by electron-phonon scattering

Recent studies have revealed the significance of electron-phonon interaction (EPI) in phonon transport at intermediate temperatures. In some metals, the EPI can even dominate over the anharmonic phonon-phonon (ph-ph) scattering, leading to an anomalous phonon transport regime in which the lattice thermal conductivity ${\ensuremath{\kappa}}_{L}$ becomes nearly temperature ($T$) independent in contrast to the usual $1/T$ dependence. However, the experimental verification of this anomalous transport regime is very challenging due to the difficulty in separating the phonon contributions from the dominating electron ones to the measured total thermal conductivity in metals. In this work, using first-principles calculations, we predict that in bilayer graphene, the phonon transport can be driven to the anomalous regime by tuning the doping level. At high doping levels close to the Van Hove singularity, the EPI can result in a fivefold reduction of ${\ensuremath{\kappa}}_{L}$ at room temperature, and ${\ensuremath{\kappa}}_{L}$ becomes $T$ independent. This anomalous behavior is found to have its origin in three aspects: (i) mirror symmetry breaking enables direct coupling between flexural phonons, the dominant carriers of ${\ensuremath{\kappa}}_{L}$, and electrons; (ii) dominance of normal processes in the anharmonic ph-ph scattering facilitates the EPI to be more prominent; (iii) dominance of these normal ph-ph processes induces the indirect effect of EPI on ${\ensuremath{\kappa}}_{L}$. This is distinct from monolayer graphene, where the mirror symmetry prohibits the direct scattering of the flexural phonons by electrons and only the indirect EPI affects ${\ensuremath{\kappa}}_{L}$. This work gives insight into the manipulation of heat conduction via externally induced EPI in two-dimensional materials in which mirror symmetry breaks and normal processes dominate the ph-ph scattering.