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

We report a detailed characterization of an unique 3-fold commensurate insulating state in single crystals of the organic π - inorganic d hybrid Cu(DMe-DCNQI)2 systems with deuterated and partially deuterated DCNQI ring, by means of low-frequency dielectric spectroscopy. A broad relaxation mode of strength Δξ≈103-104 centred at vo≈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 freedom. Both, the relaxation strength and the mean relaxation time (to=1/2πvo) are much larger than that expected for single-particle excitations. These features suggest the origin of the dielectric relaxation as an intrinsic property of the N = 3 charge density wave state