Low frequency dielectric permittivity of quasi-one-dimensional conductor (TMTTF)₂Br

Abstract:

Conductivity and permittivity ε of the organic transfer salt (TMTTF)₂Br have been measured at low frequencies (10²-10⁷ Hz) between room temperature down to 4 K. The real part of the permittivity, ε′, is shown to grow below the temperature Tρ at which the conductivity is maximum due to charge localization of Mott-Hubbard type. ε′ reaches a maximum of 10⁵-10⁶ at 35 K-50 K depending on the samples. Decreasing temperature below Tρ, ε′ sharply decreases down to helium temperature through the antiferromagnetic phase transition at T _N = 15 K. We explain the magnitude, the temperature and frequency dependence of ε′ as resulting from short range charge density wave states in the temperature range where charge localization occurs. This interpretation is supported by recent X-ray scattering measurements.