Superconducting Condensation Energy of the Two-Chain Hubabrd Model in the Bulk Limit

Abstract

We have calculated the ground state energy of the two-chain Hubbard model by using the variational Monte Carlo method for the various values of the interchain transfer energies td. The energy gain per site in the variational BCS state in reference to the normal state energy, which is nothing but the superconducting condensation energy, was obtained. We have fitted \Delta E as a function of the inverse of the lattice size by a power-law function and found that in the bulk limit \Delta E remains finite in a certain narrow range of td. We observed in calculated momentum distribution fuunctions that the superconductivity is most stable in the case where the electron distribution in k-space is in a one-band-like situation, on the brink of transition to a two-band-like one. The SDW-type trial wave function was also examined but we did not obtain any energy gain with in in the above-mentioned superconducting region.