Tunable interplay between light and heavy electrons in twisted trilayer graphene

Abstract

In systems with multiple energy bands, the interplay between electrons with different effective masses drives correlated phenomena that do not occur in single-band systems. Magic-angle twisted trilayer graphene is a tunable platform for exploring such effects, hosting both heavy electrons in its flat bands and delocalized light Dirac electrons in dispersive bands. Superconductivity in this system spans a wider range of phase space than moiré materials without dispersive bands, suggesting that interband interactions influence the stabilization of correlated phases. Here we investigate the interplay between the light and heavy electrons in magic-angle twisted trilayer graphene by performing local compressibility measurements with a scanning single-electron-transistor microscope. We establish that weak incompressibility features near several integer moiré band fillings host a finite population of light Dirac electrons at the Fermi level, despite a gap opening in the flat band sector. At higher magnetic field near charge neutrality, we find a phase transition sequence that is robust over nearly 10 μm but exhibits complex spatial dependence. Calculations establish that the Dirac sector can be viewed as flavour analogous to the spin and valley degrees of freedom.