When Disorder Unlocks: Delocalization and Quantum Geometry in Magic-Angle Graphene

Magic-angle twisted bilayer graphene (MATBG) hosts ultra-flat moiré bands that enable a remarkable landscape of correlated phases, including unconventional superconductivity. Yet every real device carries a degree of unavoidable disorder—charge puddles, strain, substrate inhomogeneity—so a central question remains: how robust are these exotic states once realistic imperfections are accounted for?To address this head-on, we performed large-scale quantum-transport simulations using a realistic tight-binding model of MATBG, allowing us to track how disorder reshapes transport length scales within and beyond the flat-band window. We uncover a striking, counter-intuitive regime: inside the flat bands, the mean free path can increase as disorder is enhanced, revealing a disorder-induced delocalization mechanism that sharply contrasts with the conventional monotonic degradation expected at higher energies. Importantly, this transport anomaly is mirrored by a disorder-dependent quantum metric—a quantum-geometric marker tied to ground-state localization—indicating that even “weak” disorder can significantly renormalize quantum-geometric ingredients that are widely discussed as key to MATBG superconductivity and related correlated phenomena.For experiments, the message is practical and testable: disorder should not be treated only as a nuisance, but as a parameter with a distinct flat-band fingerprint. Our results offer a quantitative route to rationalize device-to-device variability and motivate targeted protocols—energy/filling-resolved transport mapping while systematically tuning the disorder landscape via dielectric environment, screening, and substrate choice—to capture the predicted non-monotonic trend and the crossover back to standard localization at stronger disorder.