Quantum Monte Carlo study of the superconducting Kosterlitz-Thouless transition of the attractive Hubbard model on a triangular lattice

We study the superconducting Kosterlitz-Thouless (KT) transition of the attractive Hubbard model on a two-dimensional triangular lattice using auxiliary field quantum Monte Carlo method for system sizes up to 14x14 sites. Combining three methods to analyze the numerical data, we find, for the attractive interaction of U=-4t, that the transition temperature is broadly maximized around the band filling of 1.2 < n < 1.6, while it is found to be rather low in the range of n < 1 and n > 1.8. We discuss that this band filling dependence may be explained in terms of the band filling dependence of the superfluid density and the effective mass. Our analysis also teaches us that the estimation of the KT transition temperature requires some caution when the density of states near the Fermi level is small and the calculation is restricted to small system sizes.