Superconductivity, pseudogap, and phase separation in topological flat bands: a quantum Monte Carlo study

Abstract

We study a two-dimensional model of an isolated narrow topological band at partial filling with local attractive interactions. Numerically exact quantum Monte Carlo calculations show that the ground state is a superconductor with a critical temperature that scales nearly linearly with the interaction strength. We also find a broad pseudogap regime at temperatures above the superconducting phase that exhibits strong pairing fluctuations and a tendency towards electronic phase separation; introducing a small nearest neighbor attraction suppresses superconductivity entirely and results in phase separation. We discuss the possible relevance of superconductivity in this unusual regime to the physics of flat band moiré materials, and as a route to designing higher temperature superconductors.

We now also include weak nearest-neighbor attractive interactions and find phase separation instead of superconductivity (new Fig. 4)