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 the interchain hopping deforms the nested Fermi surface and suppresses the Spill Susceptibility. The obtained results for the Superconductivity in the Hubbard model,show qualitative agreement with recent renormalization group studies, and have the possibility of accounting for the recent experimental result of (TMTTF)(2)SbF6, whose transition temperature increases by applying pressure. 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(x2-y2) and d(xy)-wave symmetry, and find that the particle-particle interaction vertex for d(x2-y2)-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: This means that the and d(xy)-wave superconductivity compete with cacti other even if V is small. We clarify the qualitative difference in the effect of dimensionality between the d(x2-y2)-wave superconductivity.