Resonating Valence Bond Theory of Superconductivity for Dopant Carriers:   Application to the Cobaltates
  Within the $t$--$J$ model Hamiltonian we present a RVB mean field theory directly in terms of dopant particles. We apply this theory to $\mathrm{Na}_{x}\mathrm{CoO_{2}}\cdot y% \mathrm{H_{2}0}$ and show that the resulting phase diagram $T_c$ versus doping is in qualitative agreement with the experimental results. 
Alvaro Ferraz, Evgueny Kochetov, and Marcin Mierzejewski