M. Dressel et al., THE INFRARED OPTICAL-PROPERTIES OF THE ALPHA-PHASE ORGANIC SUPERCONDUCTOR, ALPHA-(BEDT-TTF)2(NH4HG(NCS)4), Synthetic metals, 56(2-3), 1993, pp. 2923-2926
The title compound is the only known organic superconductor (T(c) = 0.
8 K) with an alpha-phase crystal structure, in which the conducting pl
ane contains single BEDT-TTF molecules with alternating orientation, r
ather than the pairs of molecules found in the higher T(c) kappa-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, a
t temperatures between 6.5 K and 300 K. The overall shape of these spe
ctra 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 kappa-phase due to the lack of dimerization of the B
EDT-TTF molecules. This causes an accentuation of the far-infrared int
raband conductivity. The vibrational features are assigned and discuss
ed.