Evolution of electron Fermi surface with doping in cobaltates
  The notion of the electron Fermi surface is one of the characteristic concepts in the field of condensed matter physics, and it plays a crucial role in the understanding of the physical properties of doped Mott insulators. Based on the t-J model, we study the nature of the electron Fermi surface in the cobaltates, and qualitatively reproduce the essential feature of the evolution of the electron Fermi surface with doping. It is shown that the underlying hexagonal electron Fermi surface obeys Luttinger's theorem. The theory also predicts a Fermi-arc phenomenon at the low-doped regime, where the region of the hexagonal electron Fermi surface along the \Gamma-K direction is suppressed by the electron self-energy, and then six disconnected Fermi arcs located at the region of the hexagonal electron Fermi surface along the \Gamma-M direction emerge. However, this Fermi-arc phenomenon at the low-doped regime weakens with the increase of doping. 
Xixiao Ma, Yu Lan, Ling Qin, Lulin Kuang, and Shiping Feng
cond-mat.str-el