Pseudogap in Doped Mott Insulators is the Near-neighbour Analogue of the   Mott Gap
  We show that the strong coupling physics inherent to the insulating Mott state in 2D leads to a jump in the chemical potential upon doping and the emergence of a pseudogap in the single particle spectrum below a characteristic temperature. The pseudogap arises because any singly-occupied site not immediately neighbouring a hole experiences a maximum energy barrier for transport equal to $t^2/U$, where $t$ is the nearest-neighbour hopping integral and $U$ the on-site repulsion. The resultant pseudogap cannot vanish before each lattice site, on average, has at least one hole as a near neighbour. The ubiquituity of this effect in all doped Mott insulators suggests that the pseudogap in the cuprates has a simple origin. 
Tudor D. Stanescu and Philip Phillips