Flat band superconductivity in the square-octagon lattice

Abstract

The discovery of superconductivity in twisted bilayer graphene has triggered a resurgence of interest in flat-band superconductivity. Here, we investigate the square-octagon lattice, which also exhibits two perfectly flat bands when next-nearest neighbour hopping or an external magnetic field are added to the system. We calculate the superconducting phase diagram in the presence of on-site attractive interactions and find two superconducting domes, as observed in several types of unconventional superconductors. The critical temperature shows a linear dependence on the coupling constant, suggesting that superconductivity might reach high temperatures in the squareoctagon lattice. Our model could be experimentally realized using photonic or ultracold atoms lattices.

Enhanced repulsively bound atom pairs in topological optical lattice ladders

“…While single-particle properties are generally well understood and have recently been measured experimentally [15][16][17][18][19], there are still many open questions relating to interacting quantum systems in these band structures, questions that cold-atom systems are perfect for exploring [20][21][22][23][24][25][26][27][28][29][30]. In this work, we investigate interacting bosons in a topological band structure where the single-particle kinetic energy is completely frustrated [31][32][33][34][35][36][37][38][39][40][41][42][43][44], and find that the topology enhances the formation of bound pairs allowing them to remain stable for higher temperatures. Going beyond the regime of perturbative interactions we find that pair superfluid phases can be engineered, prepared and detected in current optical-lattice experiments.…”

Enhanced repulsively bound atom pairs in topological optical lattice ladders

“…While single-particle properties are generally well understood and have recently been measured experimentally [15][16][17][18][19], there are still many open questions relating to interacting quantum systems in these band structures, questions that cold-atom systems are perfect for exploring [20][21][22][23][24][25][26][27][28][29][30]. In this work, we investigate interacting bosons in a topological band structure where the single-particle kinetic energy is completely frustrated [31][32][33][34][35][36][37][38][39][40][41][42][43][44], and find that the topology enhances the formation of bound pairs allowing them to remain stable for higher temperatures. Going beyond the regime of perturbative interactions we find that pair superfluid phases can be engineered, prepared and detected in current optical-lattice experiments.…”