Quantum Monte Carlo Study of the Quasi-One-Dimensional Superconductivity
  We report on the result of quantum Monte Carlo simulation of quasi-one-dimensional electron systems at 1/4-filling, considering organic superconductors such as TMTSF- and TMTTF-salts. We focus on the effect of dimensionality (interchain coupling) on superconducting fluctuation. First we consider Hubbard model which includes only on-site repulsion U. We find that the increase of interchain coupling enhances superconducting susceptibility, although it deforms the nested Fermi surface and suppresses the spin susceptibility. Next we consider an extended Hubbard model which includes nearest-neighbor repulsion V . In this case we consider the competition between different symmetries of electron pairing, d_{x^2-y^2} - and d_xy-wave symmetry, and find that the particle-particle interaction vertex for d_{x^2-y^2}-wave pairing is no longer attractive even in the region where nesting condition still holds. On the other hand, the interaction vertex for d_xy-wave pairing persists to be attractive. The obtained results for the Hubbard model show qualitative agreement with recent renormalization group study, and have the possibility of accounting for the recent experimental result of (TMTTF)2SbF6, which exhibits a wider superconducting phase than the previous studies. 
Tohru Aonuma, Yuki Fuseya and Masao Ogata