Large power dissipation of hot Dirac fermions in twisted bilayer graphene.

We have carried out a theoretical investigation of hot electron power loss P, involving electron-acoustic phonon interaction, as a function of twist angle θ, electron temperature T and electron density n in twisted bilayer graphene. It is found that as θ decreases closer to magic angle θ , P enhances strongly and θ acts as an important tunable parameter, apart from T and n . In the range of T = 1-50 K, this enhancement is ∼250-450 times the P in monolayer graphene (MLG), which is manifestation of the great suppression of Fermi velocity v of electrons in moiré flat band. As θ increases away from θ , the impact of θ on P decreases, tending to that of MLG at θ ∼ 3°. In the Bloch-Grüneisen (BG) regime, P ∼ T , n and v . In the higher temperature region (∼10-50 K), P ∼ T , with δ ∼ 2.0, and the behavior is still super linear in T , unlike the phonon limited linear-in-T (lattice temperature) resistivity ρ . P is weakly, decreasing (increasing) with increasing n at lower (higher) T , as found in MLG. The energy relaxation time τ is also discussed as a function of θ and T . Expressing the power loss P = F (T ) - F (T), in the BG regime, we have obtained a simple and useful relation F (T)μ (T) = (ev /2) i.e. F (T) = (n e v /2)ρ , where μ is the acoustic phonon limited mobility and v is the acoustic phonon velocity. The ρ estimated from this relation using our calculated F (T) is nearly agreeing with the ρ of Wu et al (2019 Phys. Rev. B 99 165112).