1. flat bands and topological polarization

Tero Tapio Heikkilä

University of Jyväskylä, Finland

30 November 2021 Tue 5 pm

                                      IBS Center for Theoretical Physics of Complex Systems (PCS), Administrative Office (B349), Theory Wing, 3rd floor

                                      Expo-ro 55, Yuseong-gu, Daejeon, South Korea, 34126 Tel: +82-42-878-8633                     

Recent observations of superconductivity in graphene-based systems have indicated the role of flattening electronic bands in promoting interactions. The size of the corresponding flat bands was quite small, in practice covering only a small fraction of the available microscopic Brillouin zone of graphene. This was reflected in the relatively small critical temperature (up to a few K) for superconductivity. This notion calls for ways to realize larger flat bands. In my talk I discuss one phenomenological approach for this, based on identifying a new type of crystalline topological insulator which instead of quantized Hall conductivity and chiral surface states exhibits quantized electrical polarization and flat band surface states covering the entire microscopic Brillouin zone. If time allows, I will also describe a mechanism where the band flattening itself results from (Hartree) interactions. This may also play a role in the recent experiments.