Shot noise probing Cooper pairs, interactions, and strange metallicity 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 "granularity" of its charge carriers remains unexplored. Shot noise provides a direct window into this aspect by revealing the effective charge, dynamics, statistics, and interactions of the carriers. We report a comprehensive shot noise investigation of MATBLG as a function of carrier density across the flatband, temperature, bias energy, and magnetic field. In the superconducting (SC) phase of the flatband, 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 state of the flatband, a universal Fano factor (F ≈ 0.43) is measured, highlighting the dominance of electron-electron interactions in the flatband. 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 granular nature of the quasiparticles can explain this observed suppression.