8,296 research outputs found
Theory of triangular lattice quasi-one-dimensional charge-transfer solids
Recent investigations of the magnetic properties and the discovery of
superconductivity in quasi-one-dimensional triangular lattice organic
charge-transfer solids have indicated the severe limitations of the effective
1/2-filled band Hubbard model for these and related systems. Our computational
studies of these materials within a 1/4-filled band Hubbard model in which the
organic monomer molecules, and not their dimers, constitute the sites of the
Hamiltonian are able to reproduce the experimental results. We ascribe the spin
gap transition in kappa-(BEDT-TTF)_2B(CN)_4 to the formation of a
two-dimensional paired-electron crystal and make the testable prediction that
the spin gap will be accompanied by charge-ordering and period doubling in two
directions. We find enhancement of the long-range component of superconducting
pairing correlations by the Hubbard repulsive interaction for band parameters
corresponding to kappa-(BEDT-TTF)_2CF_3SO_3. The overall results strongly
support a valence bond theory of superconductivity we have proposed recently.Comment: 8 pages, 7 figure
The ubiquitous 1100 charge ordering in organic charge-transfer solids
Charge and spin-orderings in the 1/4-filled organic CT solids are of strong
interest, especially in view of their possible relations to organic
superconductivity. We show that the charge order (CO) in both 1D and 2D CT
solids is of the ...1100... type, in contradiction to mean field prediction of
>...1010... CO. We present detailed computations for metal-insulator and
magnetic insulator-insulator transitions in the theta-ET materials. Complete
agreement with experiments in several theta systems is found. Similar
comparisons between theory and experiments in TCNQ, TMTTF, TMTSF, and ET
materials prove the ubiquity of this phenomenon.Comment: 3 pages, 4 eps figures; ICSM 200
Co-operative density wave and giant spin gap in the quarter-filled zigzag ladder
Strong co-operative 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, the spin-gap
transition temperatures in which are unusually high.Comment: 4 pages, 4 EPS figures. accepted in Physical Review Letter
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