Nuclear Spin-Lattice Relaxation and EPR Studies of TTF-TCNQ and TMTTF-TCNQ Under Hydrostatic Pressure

The quasi one-dimensional metallic character of TTF-TCNQ has been established by measurements of electrical conductivity, magnetic susceptibility, thermoelectric power, microwave conductivity and optical reflectivity at ambient pressure1. The metallic character of TMTTF-TCNQ is discussed in the preceding report2 in comparison with that of TTF-TCNQ. The metallic state results from the strong n-orbital overlap along the TCNQ and TTF chains. In TTF-TCNQ both chains are metallic with transfer integrals of order 0.1 eV. The intetchain transfer integral is of the order of 1 meV, which shows that the interchain hopping time of electrons is much shorter than the characteristic time scale of electron spin dynamics (Ωs, T ls) and nuclear spin relaxation. Therefore, the ratio of the spin-lattice relaxation times of each chains observed by Rybaczewski et al.3 using deuterated TTF-TCNQ which is nearly independent of the temperature down to 60 K indicates a temperature independent ratio of the static susceptibilities of the individual chains. Under these conditions, the nuclear spin relaxation rate T −1 1 should be related to the observed spin susceptibility x s by the Korringa relation, (T 1 T)−1 ∞ A2x2 sK(u, T), where K is the Korringa enhancement factor which depends on the electron-.electron Coulomb correlation u and temperature T.