Variational Study of Magnetic Ordered State in d-p Model

Recent experimental studies argued that, if carefully annealed, electron-doped (n-type) cuprates become superconducting (SC) in non-doped as well as weakly doped samples, in marked contrast to the conventional recognition. This metallic (SC) behavior is not likely to be understood by means of the t-J or Hubbard models, because their ground states at half filling are insulating with antiferromagnetic (AF) orders, even for moderately frustrated cases. Thus, we systematically study a d-p model including in-plain oxygen-p and copper-d orbitals, using a variational Monte Carlo method with refined correlation factors. It is found that an AF order becomes robust as charge transfer gap Δ or coulomb interaction on Cu sites Ud becomes large. As O-to-O hopping integral t′ becomes large, the AF ordered state tends to be unstable.