title: Exact bond ordered ground state for the transition between the band and the Mott insulator.
abstract: We derive an effective Hamiltonian H(eff) for an ionic Hubbard chain, valid for t<<U,Delta, where t is the hopping, U is the Coulomb repulsion, and Delta is the charge-transfer energy. H(eff) is the minimal model for describing the transition between the band insulator (BI) (Delta-U>>t) and the Mott insulator (MI) (U-Delta>>t). Using spin-particle transformations [Phys. Rev. Lett. 86, 1082 (2001)]], we map H(eff)(U=Delta) into an SU(3) antiferromagnetic Heisenberg model whose exact ground state is known. In this way, we show rigorously that a spontaneously dimerized insulating ferroelectric phase appears in the transition region between the BI and the MI.
authors.affiliation: Center for Nonlinear Studies and Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: C D
authors.initials: CD
authors.lastname: Batista
authors.forename: A A
authors.initials: AA
authors.lastname: Aligia