Magnetoresistance of TTF-TCNQ

Abstract

The magnetoresistance of TTF-TCNQ has been measured for currents along the crystallographic b axis in static fields of 50 kOe for temperatures between 17 and 98 K. For [Formula: see text] the magnetoresistance Δρ/ρ = [ρ(50 kOe) − ρ(0)]/ρ(0) is less than 0.1% in magnitude. There is a peak of about −1.4% at 52.8 ± 0.2 K. Below 50 K, Δρ/ρ is small and negative and is described reasonably well by the formula Δρ/ρ = −(1/2)(μBH/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 behavior is consistent with that expected for a metal in the short scattering time limit [Formula: see text]. We attribute the peak at 52.8 K to the suppression of the metal–insulator transition by the magnetic field, and we show why such behavior would be expected for a Peierls transition. In the low temperature region the crystal acts like a small gap semiconductor for which the –T−2 dependence of Δρ/ρ is easily understood. We note that the peak in the magnetoresistance at 52.8 K strongly suggests that the electronic energy gap goes to zero at this temperature. One is then led to conclude that the decrease in the conductivity between 58 and 53 K is due to resistive fluctuations above the metal–insulator transition.