Condensed Matter Theory Seminar | April 29, 14:00

Superconductivity, charge density wave, and supersolidity in flat bands with tunable quantum metric

Johannes Hofmann

Predicting the fate of an interacting system in the limit where the electronic bandwidth is quenched is often highly non-trivial. The complex interplay between interactions and quantum fluctuations driven by the band geometry can drive a competition between various ground states, such as charge density wave order and superconductivity. In this work, we study an electronic model of topologically-trivial flat bands with a continuously tunable Fubini-Study metric in the presence of on-site attraction and nearest-neighbor repulsion, using numerically exact quantum Monte Carlo simulations. By varying the electron filling and the spatial extent of the localized flat-band Wannier wavefunctions, we obtain a number of intertwined orders. These include a phase with coexisting charge density wave order and superconductivity, i.e., a supersolid. In spite of the non-perturbative nature of the problem, we identify an analytically tractable limit associated with a `small' spatial extent of the Wannier functions, and derive a low-energy effective Hamiltonian that can well describe our numerical results. If time permits, I will also discus some preliminary quantum Monte Carlo results for twisted bilayer graphene at charge neutrality.


Weizmann Institute
Seminar Room 0.01, ETP and Zoom (https://uni-koeln.zoom.us/j/92165384988)
Contact: Simon Trebst