Phase separation and the existence of superconductivity in a one-dimensional copper-oxygen model.

Abstract

The phase-separation instability occurring with increasing nearest-neighbor repulsion $V$ in a two-band Hubbard model (CuO chain) is discussed. Quantum Monte Carlo simulations indicate that this transition is strongly discontinuous if the filling fraction $〈n〉$ is close to 1 (half-filled lower band). Spin-density-wave fluctuations then dominate before phase separation. Superconducting fluctuations dominate in the neighborhood of phase separation only at considerably higher doping levels, where the transition to the phase-separated state is much smoother.