Two Generalizations of $\eta$ Pairing in Extended Hubbard Models
  A rigorous result about Hubbard model obtained by C.N.Yang [Phys.Rev.Lett.63,2144(1989)] is generalized to two kinds of extended Hubbard models. One is the Hubbard model in two-dimensional triangular lattice, and the other is the Hubbard model for high spins fermions. We obtain the conditions under which a modified $\eta$-pairing operator is an eigen-operator, thus these models have a series of eigenstates possessing off-diagonal long-range order. 
Hui Zhai