Spin injection characteristics of conducting polymer nanofibers in high magnetic and electric fields

Lee, H. J.1; Kaiser, A. B.2; Jhang, S. H.1; Lee, S. H.1; Choi, A. J.1; Yoo, J. S.1; Kim, H. S.1; Aleshin, A. N.3; Goh, M. J.4; Akagi, K.4; Kaner, R. B.5; Brooks, J. S.5; Park, Y. W.1 1Republic of Korea; 2New Zealand; 3Russian Federation; 4Japan; 5United States

We have measured the current-voltage characteristics of polyacetylene and polyaniline nanofibers at high magnetic fields to determine the nature of conduction in polyacetylene, a unique material in which the lowest-energy charge excitations are predicted to be spinless charged solitons rather than electrons and holes. We show that in polyacetylene at low temperatures and high electric fields (where soliton-pair creation is most likely to be observed), there is no detectable effect on conduction of magnetic fields of all magnitudes up to the measurement limit of 30 tesla. On the other hand, our measurements on polyaniline nanofibers reveal a large magnetoresistance that shows no decrease in similar electric fields. Thus we find evidence for spinless charge carriers in polyacetylene but not in polyaniline. The results are analyzed as following. At low electric field, the electrons which carry charge and spin, are injected from one soliton site and tunnel to the next soliton site (inter-soliton electron tunnelling). At high electric field, the solitons which carry charge but no spin, tunnel through the polyacetylene chain, so that no magneto resistance is detected up to 30 tesla at high electric field. For polyaniline, the polarons which carry charge and spin are responsible for the conduction. An electric field modulated high magnetic field switching device can be envisaged as a potential application of polyacetylene nanofibers.

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