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

Abstract

We report on dc and microwave experiments of the low-dimensional organic conductors (TMTSF)${}_2$PF${}_6$ and (TMTSF)${}_2$ClO${}_4$ along the $a$, $b^{\prime }$, and $c^{\ast }$ directions. In the normal state of (TMTSF)${}_2$PF${}_6$ below T=70 K, the dc resistivity follows a power-law with ${\rho }_a$ and ${\rho }_{b^{\prime }}$ proportional to $T^2$ while ${\rho }_{c^{\ast }}\propto T$. Above $T=100$ K the exponents extracted from the data for the $a$ and $c^{\ast }$ axes are consiste1nt with what is to be expected for a system of coupled one-dimensional chains (Luttinger liquid) and a dimensional crossover at a temperature of about 100 K. The $b^{\prime }$ axis shows anomalous exponents that could be attributed to a large crossover between these two regimes. The contactless microwave measurements of single crystals along the $b^{\prime }$-axis reveal an anomaly between 25 and 55 K which is not understood yet. The organic superconductor (TMTSF)${}_2$ClO${}_4$ is more a two-dimensional metal with an anisotropy ${\rho }_a/{\rho }_{b^{\prime }}$ of approximately 2 at all temperatures. Such a low anisotropy is unexpected in view of the transfer integrals. Slight indications to one-dimensionality are found in the temperature dependent transport only above 200 K. Even along the least conducting $c^{\ast }$ direction no region with semiconducting behavior is revealed up to room temperature.

11 pages, 10 figures