Scaling Behavior of the Longitudinal and Transverse Transport in Quasi\n One-Dimensional Organic Conductors

Abstract

We report on dc and microwave experiments of the low-dimensional organic\nconductors (TMTSF)$_2$PF$_6$ and (TMTSF)$_2$ClO$_4$ along the $a$,\n$b^{\\prime}$, and $c^*$ directions. In the normal state of (TMTSF)$_2$PF$_6$\nbelow T=70 K, the dc resistivity follows a power-law with $\\rho_a$ and\n$\\rho_{b^{\\prime}}$ proportional to $T^2$ while $\\rho_{c^*}\\propto T$. Above $T\n= 100$ K the exponents extracted from the data for the $a$ and $c^*$ axes are\nconsiste1nt with what is to be expected for a system of coupled one-dimensional\nchains (Luttinger liquid) and a dimensional crossover at a temperature of about\n100 K. The $b^\\prime$ axis shows anomalous exponents that could be attributed\nto a large crossover between these two regimes. The contactless microwave\nmeasurements of single crystals along the $b^{\\prime}$-axis reveal an anomaly\nbetween 25 and 55 K which is not understood yet. The organic superconductor\n(TMTSF)$_2$ClO$_4$ is more a two-dimensional metal with an anisotropy\n$\\rho_a/\\rho_{b^{\\prime}}$ of approximately 2 at all temperatures. Such a low\nanisotropy is unexpected in view of the transfer integrals. Slight indications\nto one-dimensionality are found in the temperature dependent transport only\nabove 200 K. Even along the least conducting $c^*$ direction no region with\nsemiconducting behavior is revealed up to room temperature.\n