Freezeout of the electrical resistivity of (BEDT-TTF)2I3 below 20 K

At temperatures above 20K, the resistivity of ET is given by: ρab = ρ0 + BT2. Below 20K, we found that the resisitivity falls significantly below ρ0. Resistance ratios ρ(300K)/ρ(2K) exceed several thousand and sometimes even exceed 104. The freezeout at temperatures just below the phonon frequency is a strong indication that the resisitivity above 20K is due to scattering by phonons. The T2 law is due to a very strong momentum-dependence of the velocity v(k), with a sharp peak at the Fermi level. This peak causes the residual resisitivity due to scattering by defects to become temperature-dependent and to diminish greatly at very low temperatures. These results resolve the mystery of the highly-anomalous behavior of the resistivity of organic metals, suggested by Heeger and Garito in 1973. We present an ab-initio theory accounting for the sharp velocity peak. The theory considers a low-density electron-gas imbedded in a highly-dispersive medium, ε0/ε∞ ≅ 20. This theory applies also to high-Tc cuprates, as well as to some other systems possessing a high dispersion.