Fragile Topology and Flat-Band Superconductivity in the Strong-Coupling Regime

In flat bands, superconductivity can lead to surprising transport effects. The superfluid "mobility", in the form of weight $D_s$, does not draw from curvature band but has a purely band-geometric origin. mean-field description, non-zero Chern number or fragile topology sets lower bound for which, via Berezinskii-Kosterlitz-Thouless mechanism, might explain relatively high superconducting transition temperature measured magic-angle twisted bilayer graphene (MATBG). For topology, relevant system, fate this finite and beyond approximation remained, however, unclear. Here, we use numerically exact Monte Carlo simulations study an attractive Hubbard model bands with topological properties akin those MATBG. We find phase critical that scales linearly interaction strength. then investigate robustness state addition trivial may trivialize topology. Our results substantiate validity regime further stress importance flat-band superconductivity.