Variational study of conduction in doped Mott insulator in terms of   kinetic energy
  The kinetic features of holes (electrons) in the Hubbard model are studied using a variational Monte Carlo method. In doped Mott insulators (U>U_co), holes are classified, in the sense of conduction, into two categories: (i) The holes appearing in doublon-holon pairs are localized, encourage singlet pair formation, and gain the energy to induce a superconducting transition. (ii) The doped holes become carriers, make the system itinerant (superconducting or metallic), but lose the energy in the transition. These two roles are distinguished in correlated superconductivity. This feature is common to antiferromagnetic transitions at large U/t. 
H. Yokoyama, S. Tamura, K. Kobayashi, M. Ogata
cond-mat.str-el cond-mat.supr-con