Cooperative Density Wave and Giant Spin Gap in the Quarter-Filled Zigzag Electron Ladder

Abstract

Strong cooperative interactions occur between four different broken symmetries involving charge ordering and bond distortions in the quarter-filled correlated zigzag electron ladder. The ground state is singlet, with spin gap several times larger than in the spin-Peierls state of the one-dimensional quarter-filled chain with the same parameters. We propose the quarter-filled zigzag electron ladder model for several different organic charge transfer solids with coupled pairs of quasi-one-dimensional stacks, in which the spin-gap transition temperatures are unusually high.

Paired electron crystal: Order from frustration in the quarter-filled band

“…CTS zigzag ladder materials that are ρ = 1 2 have been found with spin-gap transition temperatures much larger than in 1D ρ = 1 2 SP materials 60 . The insulating ground state in this case may be understood again as a PEC state occurring in a zigzag ladder lattice, with singlet bonds oriented between the two chains 61 . Unlike the 1D case, bond orders are now modulated in several lattice directions, leading to a larger SG than for the 1D PEC case 61 .…”

“…The insulating ground state in this case may be understood again as a PEC state occurring in a zigzag ladder lattice, with singlet bonds oriented between the two chains 61 . Unlike the 1D case, bond orders are now modulated in several lattice directions, leading to a larger SG than for the 1D PEC case 61 . Interestingly, in both the linear chain and the zigzag ladder, the ρ = 1 2 PEC is obtained by simply removing alternate spin-singlet bonds from the corresponding ρ = 1 VBS, and replacing them with pairs of vacancies.…”

Infrared investigation of the charge ordering pattern in the organic spin ladder candidate (DTTTF)2Cu(mnt)2

“…This system is particularly attractive because it belongs to a family of quasi-isostructural compounds, with tunable properties depending on the counterion (M = Pt, Cu, Au, Ni) [3,4]. That the cation stacks of (DTTTF) 2 Cu(mnt) 2 have a 1 4 -filled band with delocalized charge and spin at high temperatures, and are therefore described by an electronic extended Hubbard Hamiltonian, as opposed to the localized Heisenberg spin Hamiltonian, brings additional complexity to the field.Two different theoretical models, the rectangular [4,6,7,8] and the zigzag ladder [9], have been proposed for this family of coupled stack materials (Figs. 1(d) and (e)) Although determination of the wavevector dependence of the magnon bands [10] is the strongest test of spin ladder character and can in principle distinguish between the models, inelastic neutron scattering experiments on (DTTTF) 2 Cu(mnt) 2 are limited by sample quantity and isotopic decoration requirements [11].…”

“…Two different theoretical models, the rectangular [4,6,7,8] and the zigzag ladder [9], have been proposed for this family of coupled stack materials (Figs. 1(d) and (e)) Although determination of the wavevector dependence of the magnon bands [10] is the strongest test of spin ladder character and can in principle distinguish between the models, inelastic neutron scattering experiments on (DTTTF) 2 Cu(mnt) 2 are limited by sample quantity and isotopic decoration requirements [11].…”

“…1(d) and (e)) Although determination of the wavevector dependence of the magnon bands [10] is the strongest test of spin ladder character and can in principle distinguish between the models, inelastic neutron scattering experiments on (DTTTF) 2 Cu(mnt) 2 are limited by sample quantity and isotopic decoration requirements [11]. The cations have homogeneous charge within the rectangular model and are charge ordered within the zigzag model [9]. An alternate approach to distinguishing between the models involves detailed comparison of vibrational property measurements with theoretical predictions.…”