Collective Charge Fluctuations and Superconductivity in Twisted Bilayer Graphene and Related Materials

The properties of low energy charge fluctuations in twisted bilayer graphene, and their role in superconducting pairing are analyzed. These damped collective modes are modified by Coulomb interactions and by longitudinal phonons, and they define basic excitations of twisted bilayer graphene and related materials. Charge fluctuations, modified by phonons and by moiré Umklapp processes, lead to a net attraction for small momentum transfers, and to superconductivity. The role of these excitations in other graphene arrangements is also studied.