A quantum Monte Carlo study on the superconducting Kosterlitz-Thouless   transition of the attractive Hubbard model on a triangular lattice
  We study the superconducting Kosterlitz-Thouless transition of the attractive Hubbard model on a two-dimensional triangular lattice using auxiliary field quantum Monte Carlo method for system sizes up to $12\times 12$ sites. Combining three methods to analyze the numerical data, we find, for the attractive interaction of $U=-4t$, that the transition temperature stays almost constant within the band filling range of $1.0 < n < 1.4$, while it is found to be much lower in the $n<1$ region. 
Tsuguhito Nakano and Kazuhiko Kuroki