Crossover from Weak to Strong Localization in Quasi-One-Dimensional Conductors

The crossover from weak to strong localization in the resistance of quasi-1D conductors is observed for the first time with decreasing the temperature; it occurs when the phase-breaking length becomes comparable with the localization length. The signature of the strong-localization regime is an activation-type temperature dependence of the resistance and exponentially strong negative magnetoresistance. The magnetoresistance is well described by the theory of doubling of the localization length in quasi-1D conductors in strong fields; this provides a direct measurement of the localization length.