Valley relaxation in a single-electron bilayer graphene quantum dot

We investigate the valley relaxation due to intervalley coupling in a single-electron bilayer graphene quantum dot. The valley relaxation is assisted by both the emission of acoustic phonons via the deformation potential and bond-length change mechanisms and $1/f$ charge noise. In the perpendicular magnetic-field dependence of the valley relaxation time T₁, we predict a monotonic decrease of T₁ at higher fields due to electron-phonon coupling, which is in good agreement with recent experiments by Banszerus et al. (arXiv:2402.16691). We find that the dominant valley relaxation channel in the high-field regime is the electron-phonon coupling via the deformation potential. At lower fields, we predict that a peak in T₁ can arise from the competition between $1/f$ charge noise and electron-phonon scattering due to bond-length change. We also find that the interlayer hopping γ₃ opens a valley relaxation channel for electric charge noise for rotationally symmetric quantum dots in bilayer graphene.