Browsing by Author "Geiser, Urs"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Analysis of the infrared conductivity of the organic superconductor α-(BEDT-TTF)2(NH4)Hg(NCS)4
    (1992) Dressel, Martin; Eldridge, John E.; Wang, H. Hau; Geiser, Urs; Williams, Jack M.
    An optical study of the α phase superconducting compound, α-(ET)2(NH4)Hg(NCS)4 has been performed. The absolute reflectivity of a deuterated crystal has been measured as a function of temperature and polarization, from which the conductivity was obtained. The overall shapes of these spectra are discussed and compared with those obtained from compounds of different phases. In particular we were able to perform a Drude fit of the low-temperature conductivity for one polarization, rather than of the reflectivity dip. The plasma frequency and damping were extracted and these yielded a reasonable effective mass and mean free path. The isotopic vibrational frequency shifts were obtained by repeating the measurements on a protonated sample, which was, however, too small to provide absolute data. The vibrational features are assigned and discussed.
  • Thumbnail Image
    ItemOpen Access
    The infrared optical properties of the α-phase organic superconductor, α-(BEDT-TTF)2(NH4Hg(NCS)4)
    (1993) Dressel, Martin; Eldridge, John E.; Wang, H. Hau; Geiser, Urs; Williams, Jack M.
    The title compound is the only known organic superconductor (Tc = 0.8 K) with an α-phase crystal structure, in which the conducting plane contains single BEDT-TT F molecules with alternating orientation, rather than the pairs of molecules found in the higher Tc k-phase compounds. We have measured the polarized reflectivity of protonated and deuterated (BEDT-TTF)2(NH4)Hg(NCS)4., from 80 cm-1 to 8000 cm-1, at temperatures between 6.5 K and 300 K. The overall shape of these spectra are discussed. The optical conductivity obtained after a Kramers-Kronig analysis shows no maximum in the mid-infrared as known from the compounds of the κ-phase due to the lack of dimerization of the BEDT-TTF molecules. This causes an accentuation of the far-infrared intraband conductivity. The vibrational features are assigned and discussed.