Microwave absorption at near-zero fields in conducting polymers

A. A. Zakhidov, I. I. Khairullin, V. Y. Sokolov, R. H. Baughman, Z. Iqbal, M. Maxfield, B. L. Ramakrishna

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Abstract

A low-field signal (LFS) of non-resonant microwave absorption is detected in nondegenerate ground state conducting polymers at relatively high temperatures and the intensity of this signal increases by three orders of magnitude on cooling to 4 K. Light n-doping of poly(p-phenylene) with sodium increases the polaron concentration and both the peak-to-peak intensity of the LFS and its onset temperature. However, in heavily n-doped or p-doped poly(p-phenylene), as well as in heat-treated ones, the LFS is strongly suppressed. Though the form of the LFS in conducting polymers is quite similar to the now well-known LFS observed in superconducting phases, its behavior as a function of magnetic field, temperature, and microwave power is different. Especially, the absence of both fine structure and hysteresis upon magnetization indicates a non-superconducting origin for the observed LFS in conducting polymers. This LFS might result from the increase of microwave absorption in low magnetic fields caused by a negative a.c. magnetoresistance due to a spin selective hopping process in a pair of two paramagnetic polarons, whose rate is reduced by field-dependent singlet-to-triplet transformation via hyperfine interaction. Spin flip on chain sites or during the hopping event provide alternate explanations for the magnetoresistance.

Original languageEnglish (US)
Pages (from-to)3717-3727
Number of pages11
JournalSynthetic Metals
Volume43
Issue number3
DOIs
StatePublished - Jun 14 1991

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ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

Zakhidov, A. A., Khairullin, I. I., Sokolov, V. Y., Baughman, R. H., Iqbal, Z., Maxfield, M., & Ramakrishna, B. L. (1991). Microwave absorption at near-zero fields in conducting polymers. Synthetic Metals, 43(3), 3717-3727. https://doi.org/10.1016/0379-6779(91)91668-Z