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Conductivity and magnetoresistance of TTF-TCNQ Tiedje, J. Thomas


Four probe d. c. electrical conductivity measurements have been made as a function of temperature on 19 single crystals of tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ). Although the data is mainly for the crystallographic b axis conductivity, some less complete a axis data is also presented. The temperature dependence of the electronic energy gap is calculated from the b axis conductivity data. The magnetoresistance for currents along the B axis of TTF-TCNQ, has been measured as a function of temperature Between 17K and 98K in static fields up to 50k0e. For T > 54K the magnetoresistance Δρ/ρ = {ρ (50k0e)- ρ(0)]/ ρ(0) is less than 0.1% in magnitude. There is a peak of about -1.4% at 52.8K. Below 50K Δρ/ρ is small and negative and is described reasonably well By the formula Δρ/ρ = -(1/2)(μ₈gH/kT)² . At all temperatures Δρ/ρ was found to be approximately independent of the orientation of the applied field with respect to the current. The high temperature behaviour is consistent with that expected for a metal in the short scattering time limit.(ω[sub c]T<<1). We attribute the peak at 52.8K to the suppression of the metal-insulator transition By the magnetic, and we show why such behaviour would be expected for a Peierls transition. In the low temperature region the crystal acts as a small gap semiconductor for which the T⁻² dependence of Δρ/ρ is easily understood.

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