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Mott transition in cuprate high-temperature superconductors

In this study, we investigate the metal-insulator transition of charge transfer type in high-temperature cuprates. We first show that we must introduce a new band parameter in the three-band d-p model to reproduce the Fermi surface of high temperature cuprates such as BSCCO, YBCO and Hg1201. We present a new wave function of a Mott insulator based on the improved Gutzwiller function, and show that there is a transition from a metal to a charge-transfer insulator for such parameters by using the variational Monte Carlo method. This transition occurs when the level difference $Δ_{dp}\equiv ε_p-ε_d$ between d and p orbitals reaches a critical value $(Δ_{dp})_c$. The energy gain $ΔE$, measured from the limit of large $Δ_{dp}$, is proportional to $1/Δ_{dp}$ for $Δ_{dp}>(Δ_{dp})_c$: $ΔE\propto -t_{dp}^2/Δ_{dp}$. We obtain $(Δ_{dp})_c\simeq 2t_{dp}$ using the realistic band parameters.