BCS theory and its strong-coupling extension have been widely successful in accounting for the properties of conventional superconductors, where phonons mediate pairing. These theoretical frameworks, however, neglect critical physical processes like the formation of competing phases or lattice polarons. This aspect has left several crucial questions in conventional superconductivity unanswered. For example, is there a maximum Tc for conventional superconductors? In this talk, I will discuss recent attempts to answer this question using numerically exact quantum Monte Carlo methods applied to the Holstein hamiltonian. I will show that many parameter regimes considered in the current literature violate the assumptions underlying this canonical toy model. These results remind us that we must be careful when using model hamiltonians to derive general conclusions about materials; however, they also direct us towards a wide-open are of research beyond BCS theory.

Host: Ambrose Seo