Mott gap collapse in electron- and hole-doped cuprates within a four-band Hubbard Model

We discuss the issue of Mott gap collapse within a selfconsistent mean field framework using a four-band Hubbard model which includes Cu $4s$ orbitals. The evolution with doping of the Fermi surface of Nd$_{2-x}$Ce$_x$CuO$_4$ (NCCO) has been investigated previously by Kusko, et al.[1] in a one-band t-t$'$-t$''$-U Hubbard model using related ARPES results[2]. The four-band model in this work confirmed the findings of the one-band model that it is necessary to employ a doping-dependent U, where U decreases with increasing doping. We also consider the hole-doped case in order to understand the doping- dependence of the peak-dip-hump structure in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. Work supported in part by the USDOE.\\ $\mbox{[1]}$C. Kusko, R.S. Markiewicz, M. Lindroos, and A. Bansil, Phy. Rev. B {\bf 66}, 140513 (2002).\\ $\mbox{[1]}$N.P. Armitage et al, Phy. Rev. Lett. {\bf 88}, 257001 (2002).