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Polaron spin current transport in organic semiconductors

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Abstract

In spintronics, pure spin currents play a key role in transmitting, processing and storing information. A pure spin current is a flow of electron spin angular momentum without a simultaneous flow of charge current. It can be carried by conduction electrons or magnons and has been studied in many inorganic metals, semiconductors and insulators, but not yet in organic semiconductors. Charge carriers in π-conjugated organic materials are localized spin-1/2 polarons which move by hopping, but the mechanisms of their spin transport and relaxation are not well understood. Here we use ferromagnetic resonance spin pumping in a ferromagnet/conjugated polymer/nonmagnetic spin-sink trilayer to demonstrate the ability of polarons to carry pure spin currents over hundreds of nanometres with long spin relaxation times of up to a millisecond and to exhibit Hanle precession. By systematically comparing charge and spin transport on the same trilayer we show that spin-orbit coupling mediates spin relaxation at room temperature.

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Figure 1: Spin current transport in the trilayer structure.
Figure 2: Observation of spin current transport in PBTTT.
Figure 3: Hanle observation in PBTTT.
Figure 4: Temperature dependences of spin current transport.

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Acknowledgements

This work was supported by the Cabinet Office, Government of Japan through its ‘Funding Program for Next Generation World-Leading Researchers’, PRESTO-JST ‘Innovative nano-electronics through interdisciplinary collaboration among material, device and system layers’, the Asahi Glass Foundation and the Engineering and Physical Sciences Research Council (EPSRC). The authors thank M. Heeney of Imperial College for supplying the PBTTT, J. Sinova of the University of Mainz for stimulating discussions, Y. Kajiwara for helping with low-temperature measurements, D. Hirobe for helping with spin pumping measurements, D. Venkateshvaran for helping with conductivity measurements, and O. Pachoumi for helping with SEM measurements. K.K. thanks the Samsung Scholarship Foundation for financial support.

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S.W. and K.A. conceived, designed, and performed the experiments, and analysed the data. S.W., K.A. and H.S. wrote the manuscript. S.W., K.K. and S.M. fabricated all devices, performed the electrical characterization, and wrote supplementary information. Y.V. performed the XPS measurements. H.K. helped with low-temperature measurements and the theoretical part. E.S. and H.S. supervised this work. All authors discussed the results and reviewed the manuscript.

Corresponding authors

Correspondence to Kazuya Ando or Henning Sirringhaus.

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The authors declare no competing financial interests.

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Watanabe, S., Ando, K., Kang, K. et al. Polaron spin current transport in organic semiconductors. Nature Phys 10, 308–313 (2014). https://doi.org/10.1038/nphys2901

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