Degeneracy of the ground states at half-filling and the existence of the η-pairing off-diagonal long-range order in the negative-U Hubbard models - Tian, G.-S. (Elsevier)
Since C.N. Yang proposed the concept of the η-pairing off-diagonal long-range order (ODLRO), its existence in the negative-U Hubbard models has been discussed by many authors. Recently, Shen and Qiu showed explicitly that the η-pairing ODLRO exists in some ground states of the negative-U Hubbard models defined on a certain type of bipartite lattices. In this article, we shall show that these states are, in fact, the only ground states which have η-pairing ODLRO. Finally, we shall briefly discuss the experimental implication of our results.
http://linkinghub.elsevier.com/retrieve/pii/0038-1098(94)90255-0
Keywords: U