Based on the Hubbard model description of the doped Mott insulator, we prove that there must exist a spinless collective excitation of charge 2e and of energy U−2μ peaked at momentum (π/a,π/a) in the non-superconducting state due to doping. Such a collective excitation arises from the electron pair correlation. Its existence is related to the breakdown of an approximate SU(2) particle-hole symmetry, from which an effective field theory of the new excitations is constructed.
@article{arxiv.cond-mat/0010470,
title = {Doping induced spinless collective excitations of charge 2e in doped Mott insulators},
author = {W. Vincent Liu},
journal= {arXiv preprint arXiv:cond-mat/0010470},
year = {2007}
}