Possible exotic phases in the one-dimensional extended Hubbard model

We investigate numerically the ground state phase diagram of the one-dimens ional extended Hubbard model, including an on-site interaction U and a near est-neighbor interaction ii. We focus on the ground state phases of the mod el in the V much greater than U region, where previous studies have suggest ed the possibility of dominant superconducting pairing fluctuations before the system phase separates at a critical value V = V-PS. Using quantum Mont e Carlo methods on lattices much larger than in previous Lanczos diagonaliz ation studies, we determine the boundary of phase separation, the Luttinger -liquid correlation exponent K-rho, and other correlation functions in this region. We find that phase separation occurs for V significantly smaller t han previously reported. In addition, for negative U, we find that a unifor m state reenters from phase separation as the electron density is increased towards half filling. For V< V-PS, our results show that superconducting f luctuations are not dominant. The system behaves asymptotically as a Luttin ger Liquid with K-rho<1, but we also find strong low-energy (but gapped) ch arge-density fluctuations at a momentum not expected for a standard Lutting er liquid. [S0163-1829(99)02503-7].