Stability of Staggered Flux State in d-p Model Studied Using Variational Monte Carlo Method

The stability of a staggered flux (SF) or d-density wave state is studied in a d-p model using a variational Monte Carlo (VMC) method. This state possesses a local circular current and possibly causes the pseudogap phase in high-T_c cuprate superconductors. We introduce into the trial function a configuration dependent phase factor, which was recently shown to be indispensable to stabilize current-carrying states. We pay attention to the energy gain as a function of adjacent O-O hopping and Cu-site coulomb repulsion U. It is found the SF state becomes stable for hole doping rates of and, owing to the reduction in kinetic energy, but seems fragile because the energy gain rapidly decays on doping holes for any. The loop current tends to increase as increases.