A L Shilov, L Elesin, M Kravtsov, J Covey, S D Ganichev, M A Kashchenko, O Popova, R Izmaylov, K Shein, I Gayduchenko, X Zhou, I Yahniuk, T Taniguchi, K Watanabe, A I Berdyugin, Y Wang, V Perebeinos, D A Svintsov, K S Novoselov, A Principi, D L Maslov, D A Bandurin
Identifying the microscopic processes limiting conductivity is essential for understanding correlated quantum materials. In twisted bilayer graphene, metallic resistivity follows ρ ~ Tα with widely varying α, fueling competing interpretations from phonon-limited transport and umklapp scattering to strange metallicity and heavy-fermion renormalization. Here, we use terahertz excitation to selectively heat electrons while keeping the lattice cold, separating electron-electron from electron-phonon contributions to resistivity. We observe a giant terahertz photoresistance - reaching several kΩ - showing that electron-electron scattering remains significant even in regimes previously attributed to phonons, including the linear-in-T resistivity near the magic angle. Away from it, photoresistance coexists with quadratic-in-T resistivity at low carrier densities where umklapp and Baber scattering are kinematically forbidden. We identify the breakdown of Galilean invariance in the Dirac dispersion, enabling inter-valley electron-electron collisions, as a possible origin. Our approach establishes terahertz-driven hot-electron transport as a framework for disentangling scattering mechanisms in low-density quantum materials.