Electron-spin-resonance studies of a family of organic conductors

Abstract

The family of organic conductors ${\left(\mathrm{TMTSF}\right)}_{2}X$, where TMTSF is tetramethyltetraselenafulvalene and $X=\mathrm{P}{{\mathrm{F}}_6}^{-}, \mathrm{As}{{\mathrm{F}}_6}^{-}, \mathrm{Sb}{{\mathrm{F}}_6}^{-}, \mathrm{N}{{\mathrm{O}}_3}^{-}, or \mathrm{B}{{\mathrm{F}}_4}^{-}$, has been studied using electron-spin-resonance techniques. Linewidth, $g$-tensor, and susceptibility data, as functions of temperature and orientation, are reported. The results imply an overall similarity among the members of the family, but some striking differences in detail are observed. We introduce a phenomenological model which explains some of the features of the linewidth anisotropy and temperature dependence. The paper includes a discussion of the metal-insulator transitions in terms of a spin-density-wave description.