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Observation of the triplet exciton in EuS-coated single-walled nanotubes

Nature Nanotechnology volume 4, pages 425–429 (2009)Cite this article

Abstract

Photon absorption by carbon nanotubes creates bound electron–hole pairs called excitons1,2,3,4,5,6,7,8, which can exist in spin-polarized triplet or spin-unpolarized singlet configurations. Triplet excitons are optically inactive owing to the weak spin–orbit coupling in nanotubes. This prevents the optical injection of electron spin into nanotubes for spintronic applications9 and limits the efficiency of photocurrent generation10. Here, we show that it is possible to optically excite the triplet exciton by using a ferromagnetic semiconductor as a spin filter11 to mix the singlet and triplet excitons. The triplet contribution to the photocurrent is detected, representing the first direct evidence of the triplet exciton in carbon nanotubes.

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Figure 1: Carbon nanotube optical transition energies and measurement geometry.
Figure 2: Europium sulphide (EuS) energy diagram and capacitive photocurrent spectrum.
Figure 3: Capacitive photocurrent spectrum of EuS-coated single-walled nanotube.
Figure 4: Magnetic field orientation dependence of the triplet peak height.

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Acknowledgements

The authors thank S. Tretiak for theoretical guidance, and for his critical reading of this manuscript. Financial support was provided by the Office of Naval Research ONR N00014-06-1-0228 and ONR N00014-06-1-0235, the National Science Foundation NSF DMR 0504158 and the U.S. Department of Energy DE-FG02-07ER46375.

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Author notes

  1. Tiffany S. Santos

    Present address: Present address: Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA,

Authors and Affiliations

  1. Department of Electrical and Computer Engineering, University of Louisville, Louisville, 40292, Kentucky, USA

    Aditya D. Mohite & Bruce W. Alphenaar

  2. Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, 02139, Massachusetts, USA

    Tiffany S. Santos & Jagadeesh S. Moodera

Authors
  1. Aditya D. Mohite
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  2. Tiffany S. Santos
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  3. Jagadeesh S. Moodera
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  4. Bruce W. Alphenaar
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Contributions

B.W.A. conceived the experiment and wrote the manuscript. A.D.M. performed the device fabrication and optical characterization. T.S.S. and J.S.M. performed material deposition. B.W.A., A.D.M. and J.S.M. designed the experiment, discussed the results and commented on the manuscript.

Corresponding author

Correspondence to Bruce W. Alphenaar.

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Mohite, A., Santos, T., Moodera, J. et al. Observation of the triplet exciton in EuS-coated single-walled nanotubes. Nature Nanotech 4, 425–429 (2009). https://doi.org/10.1038/nnano.2009.122

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