Interhole correlation and phase separation in t-J model

Interhole and interelectron correlations as well as a transition to phase separation in the t-J model near half filling are reconsidered using a variational Monte Carlo method. As a trial wave function, we use a state that can simultaneously represent a d-wave superconducting and antiferromagnetic (AF) orders and allows for nearest-neighbor hole-hole and spin-spin correlation factors and band renormalization effects. It is found that a transition occurs at J = J _PS ∼ 2.5t for the doping rates δ = 0.08 and 0.20 from a seemingly uniform state to phase separation (J > J _PS) of singly occupied sites and empty sites. For J < J _PS, where the values used for cuprate superconductors (0.25 ≲ J/t ≲ 0.5) are included, the interhole correlation is always repulsive. This result is negative to an intuitive picture for cuprates: Two holons coherently move in the background of AF orders.