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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 pi-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 \Delta\epsilon~10^3 - 10^4 centred at \nu_0~1 - 10kHz 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 (\tau_0 = 1/2\pi\nu_0) 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.

collective modes ; CDW ; metal-insulator transitions ; dielectric loss and relaxation

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