2022-12-06T05:13:44Zhttps://niigata-u.repo.nii.ac.jp/oaioai:niigata-u.repo.nii.ac.jp:000022562021-03-01T20:41:18ZA Possible Bipolaronic Transition in β-pyrochlore CompoundsA Possible Bipolaronic Transition in β-pyrochlore CompoundsFuse, T.7659Ono, Y.62β-Pyrochlore oxideKOs2O6Bipolaronic transitionHubbard–Holstein modelWe 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.journal articleElsevier2010-12application/pdfPhysica. C, Superconductivity and its applicationsSupplement 1470S701S702Physica. C, Superconductivity and its applicationsAA1146198409214534https://niigata-u.repo.nii.ac.jp/record/2256/files/980.pdfenginfo:doi/10.1016/j.physc.2010.01.022