Exact-diagonalization study on the effect of the long-range Coulomb interaction to the superconducting ground state in the two-chain Hubbard model

We present exact-diagonalization results clearly indicating that the long-r ange part of Coulomb interaction does not sweep away the superconducting re gion of the two-chain Hubbard model driven by the short-range part. When th e model contains the nearest-neighbor Coulomb interaction both for the inte rchain and the intrachain directions, the region of developed superconducti ng correlations in the ground state is reduced. The CDW correlation is foun d to increase, intervening with the competition between superconductivity a nd CDW. When we include the long-range Coulomb interaction of the type of 1 /r, the instability to the CDW state weakens with the superconducting regio n recovered to some extent compared with the above case. (C) 1998 Elsevier Science B.V. AU rights reserved.