Electronic structure of some β -( C 10 H 8 <mml:…
1987; American Physical Society; Volume: 35; Issue: 18 Linguagem: Inglês
10.1103/physrevb.35.9605
ISSN1095-3795
AutoresClaus S. Jacobsen, D. B. Tanner, Jack M. Williams, U. Geiser, H. H. Wang,
Tópico(s)Inorganic Chemistry and Materials
ResumoPolarized reflectance measurements have been made on two isostructural conducting compounds of bis(ethylenedithio)tetrathiafulvalene [BEDT-TTF or ET, (${\mathrm{C}}_{10}$${\mathrm{H}}_{8}$${\mathrm{S}}_{8}$)]: \ensuremath{\beta}-(ET${)}_{2}$${\mathrm{AuI}}_{2}$ and \ensuremath{\beta}-(ET${)}_{2}$${\mathrm{I}}_{2}$Br. The former is superconducting at ambient pressure with ${T}_{c}$=5 K, whereas the latter retains normal-metal conductivity to low temperatures. The reflectance measurements, made at temperatures of approximately 30 and 300 K, spanned 80 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (0.01 eV) through 33 000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (\ensuremath{\sim}4 eV); they were made for polarization along the ET molecular stacking axis and transverse to it in the sheets or layers of ET molecules. Band-structure parameters determined from the plasmon frequencies imply that the anisotropy is rather low for organic conductors, with ${t}_{?}$\ensuremath{\approxeq}0.22 eV and ${t}_{\ensuremath{\perp}}$\ensuremath{\approxeq}0.09 eV for \ensuremath{\beta}-(ET${)}_{2}$${\mathrm{AuI}}_{2}$; ${t}_{?}$\ensuremath{\approxeq}0.18 eV and ${t}_{\ensuremath{\perp}}$\ensuremath{\approxeq}0.07 eV for \ensuremath{\beta}-(ET${)}_{2}$${\mathrm{I}}_{2}$Br. At 300 K, the spectra differ substantially from the expectations of simple one-electron models, suggesting that both electron-phonon and electron-electron interactions play important roles in the electronic structure of these materials. At low temperatures, the materials display basically metallic characteristics, yet deviate significantly from simple Drude-model behavior. At 30 K, no effect attributable to superconducting fluctuations could be observed.
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