@article{oai:niigata-u.repo.nii.ac.jp:00002256,
 author = {Fuse, T. and Ono, Y.},
 issue = {Supplement 1},
 journal = {Physica. C, Superconductivity and its applications, Physica. C, Superconductivity and its applications},
 month = {Dec},
 note = {We investigate the Hubbard–Holstein model by using the dynamical mean-field theory combined with the exact diagonalization method. Below a critical temperature Tcr, a coexistence of two solutions, small lattice fluctuating solution (polaronic state) and large one (bipolaronic state), is found for the same value of the electron–phonon coupling g in the range gc1<g<gc2 for a fixed value of the Coulomb interaction U. As the result, the system shows a first-order phase transition at Tp(<T cr) from the bipolaronic to the polaronic states as T decreases. The effective potential for oscillating atoms, which is renormalized due to the effect of g, is double-well type for T>Tp, while it is single-well type for T<Tp. The obtained transition for small U case with small Tp and discontinuities in physical quantities seems to be account for the rattling transition observed in the β-pyrochlore oxide KOs2O6.},
 pages = {S701--S702},
 title = {A Possible Bipolaronic Transition in β-pyrochlore Compounds},
 volume = {470},
 year = {2010}
}