Shot noise probing "granularity" in magic angle twisted bilayer graphene

Magic-angle twisted bilayer graphene (MATBLG), a promising platform for exploring strongly correlated electron physics, exhibits a rich phase diagram unveiled by various transport and thermodynamic probes, yet the microscopic nature or "discreteness" of its charge carriers remains unexplored. Shot noise provides a direct window into this aspect by revealing the effective charge, dynamics, and interactions of the carriers. We report a comprehensive investigation of shot noise in MATBLG as a function of carrier density across the flat bands, temperature, bias energy, and magnetic field. In the superconducting (SC) phase of the flat band, a doubling of the Fano factor (F ≃ 2) is observed, signifying charge transport via Cooper pairs, providing unambiguous evidence of electron pairing. In the normal states (non-SC region) of the flat band at the base temperature (Te = 40mK), a universal Fano factor (F ≃ 0.43) is measured, highlighting the dominance of electron-electron interactions in the flat bands. Most strikingly, around the SC dome, we observe a strong suppression of the Fano factor (F ≃ 0.15) above the critical current. Considering various possibilities, our results suggest that a lack of sharp quasiparticles can explain this observed suppression when superconductivity is destroyed.