Infrared studies of low-temperature symmetry breaking in the perrhenate family of ET-based organic molecular conductors

Autor: R.G. Daugherty, M. E. Kelly, Zhengtao Zhu, S.M. Baker, Jack M. Williams, Janice L. Musfeldt, J. Dong, John A. Schlueter, G. Li
Rok vydání: 1999
Předmět:
Zdroj: Physical Review B. 60:931-941
ISSN: 1095-3795
0163-1829
DOI: 10.1103/physrevb.60.931
Popis: The polarized infrared and optical reflectance spectra of several members of the bis-(ethylenedithio)-tetrathiafulvalene (ET) complexed with perrhenate class [(ET){sub 2}(ReO{sub 4}), {alpha}-(ET){sub 3}(ReO{sub 4}){sub 2}, {beta}-(ET){sub 3}(ReO{sub 4}){sub 2}] of organic molecular solids have been measured as a function of temperature. For the compounds studied, the spectra are highly anisotropic, with data in the good conductivity polarization dominated by totally symmetric electron-phonon activated A{sub g} modes of ET. The low-temperature phase of each material is characterized by the opening of a semiconducting gap and vibronic symmetry breaking, as evidenced by vibrational fine structure in varying degrees. The nature and splitting of the 900-cm{sup {minus}1} perrhenate mode through the phase-transition temperatures implies that anion ordering drives the phase transition in the two 3:2 phases whereas the 82-K metal {r_arrow} insulator transition in (ET){sub 2}(ReO{sub 4}) is a weak structural modification in which anion reordering plays a minimal role. Correlation effects in this set of compounds are important, suggesting that a Hubbard gap picture may be appropriate for interpreting the low-lying electronic structure in these organic molecular solids. {copyright} {ital 1999} {ital The American Physical Society}
Databáze: OpenAIRE
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