Spin Lattice Relaxation as a Probe of Carrier Dynamics in Conducting Polymer Poly-3-methyl-thiophene

Measurements of the proton spin lattice relaxation rate (1/$T_{1})$ in the conducting polymer poly-3-methyl-thiophene doped with PF$_{6}$ are reported over the temperature ($T)$ and magnetic field ($B_{0})$ ranges 2-300 K and 0.9-9.0 T respectively. They yield information regarding local magnetic fluctuations from charge carrier dynamics. Their dependence on $T$ and $B_{0}$ deviate from the Korringa law for 1/$T_{1}$ in metals. Below 35 K, two values for 1/$T_{1}$ are observed. At higher $T$, a more uniform relaxation is observed. These results suggest that localized and itinerant electrons are present in different regions of the sample, depending on $T$ and the degree of sample disorder. This interpretation is further supported by magnetic susceptibility measurements, which demonstrate Fermi glass behavior at low $T$. From these 1/$T_{1}$ measurements, the disordered fraction of our samples is obtained. This work was supported by NSF Grants DMR-0334869 and INT-0225578 (WGC), and DMR-0203806 (SEB).