Symmetry crossover and excitation thresholds at the neutral-ionic transition of the modified Hubbard model

Abstract

Exact ground states, charge densities and excitation energies are found using valence bond methods for N-site modified Hubbard models with uniform spacing. At the neutral-ionic transition (NIT), the ground state has a symmetry crossover in 4n, 4n+2 rings with periodic and antiperiodic boundary conditions, respectively. The modified Hubbard model has a continuous NIT between a diamagnetic band insulator on the paired side and a paramagnetic Mott insulator on the covalent side. The singlet-triplet (ST), singlet-singlet (SS) and charge gaps for finite N indicate that the ST and SS gaps close at the NIT with increasing U and that the charge gap vanishes only there. Finite-N excitations constrain all singularities to about 0.1t of the symmetry crossover. The NIT is interpreted as a localized ground state (gs) with finite gaps on the paired side and an extended gs with vanishing ST and SS gaps on the covalent side. The charge gap and charge stiffness indicate a metallic gs at the transition that, however, is unconditionally unstable to dimerization.

12 pages, including 8 figures

References in corpus (1)

• From band insulator to Mott insulator in one dimension

Cited by in corpus (21)

• Quantum critical behavior of the one-dimensional ionic Hubbard model
• Ground-state phase diagram of the one-dimensional half-filled extended Hubbard model
• Supramolecular interactions in clusters of polar and polarizable molecules
• Nature of the insulating phases in the half-filled ionic Hubbard model
• Dielectric response of modified Hubbard models with neutral-ionic and Peierls transitions
• Giant infrared intensity of the Peierls mode at the neutral-ionic phase transition
• Tuning the bond order wave (BOW) phase of half-filled extended Hubbard models
• Neutral-ionic phase transition : a thorough ab-initio study of TTF-CA
• Transition from band insulator to Mott insulator in one dimension: Critical behavior and phase diagram
• Intermediate regime in Tetrathiafulvalene-Chloranil (TTF-CA) pressure-induced neutral-ionic transition
• Pressure driven neutral-ionic transition in ClMePD-DMeDCNQI
• The Valence Transition Model of Pseudogap, Charge-Order and Superconductivity in Electron- and Hole-Doped Copper Oxides
• Dispersive Excitations in the One-Dimensional Ionic Hubbard Model
• Is there a superconducting phase in the half-filled ionic Hubbard model ?
• Finite-temperature phase transitions in the ionic Hubbard model
• Effects of Lattice and Molecular Phonons on Photoinduced Neutral-to-Ionic Transition Dynamics in Tetrathiafulvalene-$p$-Chloranil
• Sr${}_2$RuO${}_4$, like doped cuprates and barium bismuthate, is a negative charge-transfer gap even parity superconductor with $\frac{3}{4}$-filled oxygen band
• Ab-Initio Calculation of the Metal-Insulator Transition in Sodium rings and chains and in mixed Sodium-Lithium systems
• Gutzwiller projection for exclusion of holes: Application to strongly correlated Ionic Hubbard Model and Binary Alloys
• External Electric Field Mediated Quantum Phase Transitions in One-Dimensional Charge Ordered Insulators: A DMRG Study
• Möbius molecules and fragile Mott insulators