Bond and charge-density waves in(DI−DCNQI)2Ag(DI−DCNQI

Abstract

The charge distribution and molecular arrangement of a quarter-filled quasi-one-dimensional system ͑DI-DCNQI͒ 2 Ag ͑DI-DCNQI=2,5-diiodo-dicyanoquinediimine͒ has been studied by IR and Raman spectroscopy. The charge localization of this material was believed to be a one-dimensional generalization of a Wigner crystal driven by intersite Coulomb repulsion. While charge disproportionation is confirmed via the splitting of b u modes in the infrared spectrum, the appearance of intense IR vibronic bands of a g modes strongly suggests the presence of the dimerization that is not expected by the proposed 1010 charge ordering model. In addition, the selection rules for the IR and Raman signals cannot be explained without a further symmetry reduction of the unit cell. To explain the vibrational behavior observed for a single crystal, we show that a more appropriate model for the charge ordering is 0110 ͑2k F charge-density wave and 4k F bond-order wave͒.

Photochemical modification of magnetic properties in organic low-dimensional conductors

“…5 and 6, respectively. The physical behavior of the pristine salt quantitatively agreed with previously reported one [32][33][34][35][36][37][38][39][40][41][42][43]. Ag(DI) 2 exhibited semiconducting behavior, i.e.…”

“…On the other hand such dispersion was not observed when the polarization was perpendicular to the c axis (c-spectrum). This indicates that the conduction should occur only along the c axis, showing the onedimensionality of the electronic structure of Ag(DI) 2 and being consistent with a previous optical study of this salt [43]. After UV irradiation for 6 h, the spectra became featureless irrespective of the polarization directions.…”

Wigner Crystallization in(DI−DCNQI)2AgDetected by Synchrotron Radiation X-Ray Diffraction

“…The dimerization of the molecules shows that columns B and C are in the bond order wave (BOW) state; column B is in a mixture of CO and BOW states, while column C is in a pure BOW state. This structure, in which three kinds of columns are aligned, is unprecedented for Q1D compounds and differs from any of the previous studies on this compound [8,12].…”

“…If the Bravais lattice at the LT phase is tetragonal, only one space group of the 2c p -cell structure is possible within the limitations of the subgroup for I4 1 =a: P 4. However, this space group contradicts the experimental results of the persistence of inversion symmetry obtained by optical measurement [12,13]. Since there is no candidate having an inversion center in the tetragonal subgroups, the crystal system in the LT phase has to be monoclinic.…”

Characterization of the quasi-one-dimensional compounds δ-(EDT-TTF-CONMe2)2X, X=AsF6 and Br by vibrational spectroscopy and density functional theory calculations

“…In several compounds originating from the TTF family, 25 for example, TMTTF 20,26 and BEDT-TTF, 14 a linear dependence is observed between the frequency shift and the charge per molecule; this holds mainly for modes which are not subject to electron-molecular-vibrational (emv-) coupling. 27,28 Our calculations reveal several modes that exhibit a distinct frequency shift when the ionicity of the (EDT-TTF)-CONMe 2 molecule changes. With the charge on the molecule decreasing from 0 to +1e the ν 13 , ν 14 , and ν 15 modes shift down in frequency by about 40, 165, and 82 cm −1 , respectively.…”