Collective excitation of a short-range charge ordering in $\theta$-$\mbox{(BEDT-TTF)}_2\mbox{CsZn(SCN)}_4$

Abstract

We find a characteristic low-energy peak structure located in the range of 100-300 cm${}^{-1}$ in the optical conductivity spectra of a quasi-two-dimensional organic compound with a triangular lattice, $\theta$-$\mbox{(BEDT-TTF)}_2\mbox{CsZn(SCN)}_4$, in which two different types of short-range charge orderings (COs) coexist. Upon lowering the temperature, the low-energy peak becomes significant and shifts to much lower frequencies only for the polarization of $E\parallel a$, in contrast to the other broad electronic bands in the mid-infrared region. On introducing disorder, the low-energy peak is strongly suppressed in comparison with the broad electronic bands. This result indicates that the low-energy peak is attributed to a collective excitation that originates from the short-range CO with a relatively long-period $3\times 3$ pattern. The present results shed light on the understanding of the low-energy excitation in the glassy electronic state, where the charge degrees of freedom remain at low temperatures.

5 pages, 3 figures, accepted for publication in Physical Review B

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Cited by in corpus (8)

• The transient localization scenario for charge transport in crystalline organic materials
• Glassy dynamics in geometrically frustrated Coulomb liquids without disorder
• Emergence of charge degrees of freedom under high pressure in an organic dimer-Mott insulator ${\beta }^{\prime }$-(BEDT-TTF)${}_2$ICl${}_2$
• Long-Period Charge Correlations in Charge-Frustrated Molecular theta-(BEDT-TTF)2X
• The metal-insulator transition in the organic conductor ${\beta }^{\prime \prime }$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$Cl
• Involvement of structural dynamics in the charge-glass formation in molecular metals
• Finite Temperature Properties of Geometrically Charge Frustrated Systems
• Dimer-Mott and charge-ordered insulating states in the quasi-one-dimensional organic conductors ${\delta }_P^{\prime }$- and ${\delta }_C^{\prime }$-(BPDT-TTF)${}_2$ICl${}_2$