Superfluidity without charge order in the attractive Hubbard model on the kagome lattice

Abstract

Using auxiliary-field quantum Monte Carlo simulations, we study the zero-temperature attractive Hubbard model on the kagome lattice at various relevant electronic fillings. The low-energy physics at $2/3$-density is influenced by the Dirac point at the Fermi energy, wherein we unveil a superfluid transition at a critical attractive interaction $U_c/t=-4.58(3)$, which belongs to the chiral-XY universality class. This U(1) symmetry-breaking is not accompanied by charge order, even for substantially large interaction strengths, in a regime where a description in terms of hardcore bosons becomes increasingly suitable. An investigation of the latter shows that charge ordering at $1/3$-filling only occurs at interaction strengths much larger than those corresponding to the mapping to the original fermionic model. Additionally, for densities exhibiting van Hove singularities in the non-interacting density of states, our results show that any attractive interaction gives rise to superfluidity, yet again without charge ordering, contrary to recent studies employing mean-field theory.