Superconductivity from skyrmion condensation in magic angle graphene
by Dr. Shubhayu Chatterjee (University of California, Berkeley)
Monday, November 16, 2020 from to (Asia/Kolkata)
We propose and analyze a strong-coupling route to superconductivity in twisted bilayer graphene near the magic angle (MATBG). Starting from a promising ordered insulating state featuring Chern bands, we argue that topological textures/skyrmions of the order parameter carry electric charge due to band topology. Subsequently, we find a natural all-electronic mechanism of attraction between two such charge e textures. This leads to pairing into charge 2e bosons, whose condensation can trigger superconductivity on doping away from the insulating state. We discuss microscopic aspects of this scenario, including energetics and an estimate of the effective mass which yields Tc for the superconductor, within the framework of an effective field theory. We back up our analytical calculations by large-scale DMRG numerics on a related model that captures the relevant symmetry and topology of the flat bands in MATBG. In DMRG, we find clear evidence for superconductivity driven by the binding of electrons into charge-2e skyrmions, even when Coulomb repulsion is by far the largest energy scale.