Restricted electron motion in 1D organic conductors: PGSE-ESR in (PE)2PF6 and (FA)2PF6

The pulsed-gradient spin echo electron spin resonance technique has been used to study the restricted motion of the conduction electrons in the one-dimensional organic conductors (PE)2PF6 and (FA)2PF6. Data were collected as a function of temperature, between room temperature and the Peierls transition temperature. Improved signal-to-noise ratio and reduced eddy currents were achieved. Echo attenuation for (PE)2PF6 was found to fit a model assuming diffusional motion between scattered, totally reflecting, barriers. The free diffusion constant and average barrier distance were successfully best fitted simultaneously for all temperatures, and the temperature dependence of the diffusion constant was found to scale with the previously measured AC conductivity. In contrast, PGSE results for the (FA)2PF6 crystals do not fit the above model, possibly due to the existence of basically different restricting factors.