1H-NMR and charge transport in metallic polypyrrole at ultra-low temperatures and highmagnetic fields

Abstract

The temperature dependence of conductivity, proton spin relaxation time(T1) and magnetoconductance (MC) in metallic polypyrrole (PPy) doped withPF6− have been carried out at mK temperatures and high magnetic fields. AtT<1 K both electron–electron interaction (EEI) and hopping contributesto conductivity. The temperature dependence of a protonT1 is classified in threeregimes: (a) for T<6 K—relaxation mechanism follows a modified Korringa relation due to EEI and disorder, (b) for6 K<T<50 K—relaxation mechanism is via spin diffusion to the paramagnetic centers and (c) forT>50 K—relaxation is due to the dipolar interaction modulated by the reorientation of the symmetricPF6 groups following the Bloembergen, Purcell and Pound (BPP) model. The data analysis showsthat the Korringa ratio is enhanced by an order of magnitude. The positive and negative MC atT<250 mK is due to the contributions from weak localization and Coulomb-correlated hoppingtransport, respectively. The role of EEI is observed to be consistent in conductivity,T1 and MC data,especially at T<1 K.