Tunable electron-phonon interactions in moire graphene

Understanding strong interactions in moire bands is key for advancing this versatile and highly tunable platform to study strongly-correlated electron physics. While strong electron-electron interactions arise naturally in flat bands, the enhanced electron-phonon interactions, evidenced by many exotic behaviors in moire graphene, have remained a mystery. Drawing inspiration from the Purcell effect in quantum optics, we argue that well-localized Wannier orbitals boost the electron-phonon interactions. Reshaping of Wannier orbitals is a prominent effect in graphene moire superlattices where the orbitals are tunable by the twist angle. Reducing the orbital effective volume leads to an enhancement in the effective el-ph coupling strength, yielding values considerably larger than those known for monolayer graphene. The enhanced coupling boosts the el-ph scattering rates, pushing them above the values predicted from the enhanced spectral density of electronic excitations. The enhanced electron-phonon interaction manifests in the observables such as the electron-lattice cooling and in the resistivity, both of which show an enhancement as large as tenfold. Strengthening interactions by the reshaped Wannier orbitals provides unique means to control the properties of moire bands.