Critical magnetic fields and electron pairing in magic-angle twisted bilayer graphene

The microscopic mechanism of superconductivity in magic-angle twisted bilayer graphene (MATBG) is currently under active debate. The authors propose here that valuable constraints are implied by the band-filling dependences of the critical temperature and the critical magnetic field, which together define an average Fermi velocity. They show that a robust inverse correlation between the critical temperature and the average Fermi velocity holds in models with band-filling independent pairing interactions. The absence of such an association in experiments suggests that the pairing glue in MATBG is strongly band-filling dependent.