Dielectric spectroscopy on the quasi–one-dimensional organic charge density wave conductor (Fluoranthene) ₂ PF ₆

Abstract

Frequency-dependent complex conductivity measurements on the organic quasione-dimensional CDW system (Fa) 2PF6 between 10 −4 Hz and 3•10 9 Hz at temperatures ranging from 20 K to 290 K are reported. Below the temperature of the Peierls transition (TP = 182 K) the real part of the conductivity exhibits two structures, which can be attributed to two modes of the charge density wave (CDW): a temperature-dependent low-frequency relaxational mode of local oscillating deformations and a high-frequency resonant mode of the pinned CDW as a whole. The measurements indicate that the damping of the relaxational mode is dominated by free carriers in the covered temperature range. At low temperatures the dynamics of the CDW in (Fa) 2PF6 shows features characteristic of the transition into a glass-like state.

Electronic crystals: an experimental overview

“…The main relaxation time τ of this mode is thermally activated in the temperature range 100 K-40 K with the same activation energy than the dc resistivity. Below 40 K, as seen in figure 6.9, below 10 Hz a peak in the dielectric function ε ′ occurs, which seems to indicate a divergence around 30 K. Thus, as o-TaS 3 and K 0.3 MoO 3 the dielectric function of (fluoranthène) 2 PF 6 shows features of a glassy state [573] down to a very low frequency (∼ 10 −4 Hz).…”

“…Dielectric spectroscopy has been also studied [573] in the CDW organic (fluoranthène) 2 PF 6 . Similarly to o-TaS 3 and K 0.3 MoO 3 a high frequency mode at 7 × 10 11 Hz was interpreted as the pinning mode; this mode appears at much higher frequency than in o-TaS 3 or K 0.3 MoO 3 , probably due to the commensurate CDW.…”