Low frequency dielectric spectroscopy of the Peierls-Mott insulating statein the deuterated copper-DCNQI systems

We report a detailed characterization of an unique 3-fold commensurate insu lating state in single crystals of the organic pi - inorganic d hybrid Cu(D Me-DCNQI)(2) systems with deuterated and partially deuterated DCNQI ring, b y means of low-frequency dielectric spectroscopy. A broad relaxation mode o f strength Delta epsilon approximate to 10(3)-10(4) centred at nu(0) approx imate to 1-10 kHz is observed in the hysteresis temperature region in which the insulating phase coexists with metallic islands. At lower temperatures , outside the nucleation range, the relaxation narrows, approaching a Debye -like form for an overdamped response of a system with a single degree of f reedom. Both, the relaxation strength and the mean relaxation time (tau(0) = 1/2 pi nu(0)) are much larger than that expected for single-particle exci tations. These features suggest the origin of the dielectric relaxation as an intrinsic property of the N = 3 charge density wave state.