Giant magnetoresistance due to electron-hole pair mechanism in poly(N-vinylcarbazole)

Tadaaki Ikoma, Toshinari Ogiwara, Yutaka Takahashi, Kimio Akiyama, Shozo Tero-Kubota, Yuka Takahashi, Tomohiro Suzuki, Yusuke Wakikawa

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


An amorphous molecular semiconductor, poly(N-vinylcarbazole) (PVCz), exhibits negative giant magnetoresistance (MR) under ambient conditions. The application of a weak magnetic field of 10 mT to PVCz films doped with lumichrome, in which light excitation immediately creates triplet electron-hole (e-h) pairs that are precursors of photocarriers, causes a steep decrease in resistivity by more than 20% at ambient temperature. Further, the resistivity of the doped film gradually reduces by approximately one-half under a field of 1 T, equivalent to an MR ratio of -55%. In addition, anomalous spikes are also detected at 0.07, 0.30, and 9.0 T, indicative of an exponential dependence with a decay distance of 0.1 nm in the exchange interaction of the e-h pair. A quantum mechanical calculation based on the density operator formalism clarifies that the observed MR effect can be comprehensively understood by the spin-selective charge dynamics and the coherent and incoherent spin dynamics of the e-h pair in a quasi-one-dimensional lattice for photocarrier generation. Model calculations also indicate the importance of the spin-lattice relaxation for the giant MR effect in organic molecular semiconductors.

Original languageEnglish
Pages (from-to)285-290
Number of pages6
JournalSynthetic Metals
Issue number3-4
Publication statusPublished - 2010 Feb


  • Electron-hole pair
  • Magnetoresistance
  • Photoconduction
  • Spin relaxation
  • Spin-selective recombination

ASJC Scopus subject areas

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


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