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Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy

In electronic-type ferroelectrics, where dipole moments produced by the variations of electron configurations are aligned, the polarization is expected to be rapidly controlled by electric fields. Such a feature can be used for high-speed electric-switching and memory devices. Electronic-type ferroe...

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Autores principales: Yamakawa, H., Miyamoto, T., Morimoto, T., Yada, H., Kinoshita, Y., Sotome, M., Kida, N., Yamamoto, K., Iwano, K., Matsumoto, Y., Watanabe, S., Shimoi, Y., Suda, M., Yamamoto, H. M., Mori, H., Okamoto, H.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Nature Publishing Group 2016
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4750076/
https://www.ncbi.nlm.nih.gov/pubmed/26864779
http://dx.doi.org/10.1038/srep20571
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author Yamakawa, H.
Miyamoto, T.
Morimoto, T.
Yada, H.
Kinoshita, Y.
Sotome, M.
Kida, N.
Yamamoto, K.
Iwano, K.
Matsumoto, Y.
Watanabe, S.
Shimoi, Y.
Suda, M.
Yamamoto, H. M.
Mori, H.
Okamoto, H.
author_facet Yamakawa, H.
Miyamoto, T.
Morimoto, T.
Yada, H.
Kinoshita, Y.
Sotome, M.
Kida, N.
Yamamoto, K.
Iwano, K.
Matsumoto, Y.
Watanabe, S.
Shimoi, Y.
Suda, M.
Yamamoto, H. M.
Mori, H.
Okamoto, H.
author_sort Yamakawa, H.
collection PubMed
description In electronic-type ferroelectrics, where dipole moments produced by the variations of electron configurations are aligned, the polarization is expected to be rapidly controlled by electric fields. Such a feature can be used for high-speed electric-switching and memory devices. Electronic-type ferroelectrics include charge degrees of freedom, so that they are sometimes conductive, complicating dielectric measurements. This makes difficult the exploration of electronic-type ferroelectrics and the understanding of their ferroelectric nature. Here, we show unambiguous evidence for electronic ferroelectricity in the charge-order (CO) phase of a prototypical ET-based molecular compound, α-(ET)(2)I(3) (ET:bis(ethylenedithio)tetrathiafulvalene), using a terahertz pulse as an external electric field. Terahertz-pump second-harmonic-generation(SHG)-probe and optical-reflectivity-probe spectroscopy reveal that the ferroelectric polarization originates from intermolecular charge transfers and is inclined 27° from the horizontal CO stripe. These features are qualitatively reproduced by the density-functional-theory calculation. After sub-picosecond polarization modulation by terahertz fields, prominent oscillations appear in the reflectivity but not in the SHG-probe results, suggesting that the CO is coupled with molecular displacements, while the ferroelectricity is electronic in nature. The results presented here demonstrate that terahertz-pump optical-probe spectroscopy is a powerful tool not only for rapidly controlling polarizations, but also for clarifying the mechanisms of ferroelectricity.
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spelling pubmed-47500762016-02-18 Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy Yamakawa, H. Miyamoto, T. Morimoto, T. Yada, H. Kinoshita, Y. Sotome, M. Kida, N. Yamamoto, K. Iwano, K. Matsumoto, Y. Watanabe, S. Shimoi, Y. Suda, M. Yamamoto, H. M. Mori, H. Okamoto, H. Sci Rep Article In electronic-type ferroelectrics, where dipole moments produced by the variations of electron configurations are aligned, the polarization is expected to be rapidly controlled by electric fields. Such a feature can be used for high-speed electric-switching and memory devices. Electronic-type ferroelectrics include charge degrees of freedom, so that they are sometimes conductive, complicating dielectric measurements. This makes difficult the exploration of electronic-type ferroelectrics and the understanding of their ferroelectric nature. Here, we show unambiguous evidence for electronic ferroelectricity in the charge-order (CO) phase of a prototypical ET-based molecular compound, α-(ET)(2)I(3) (ET:bis(ethylenedithio)tetrathiafulvalene), using a terahertz pulse as an external electric field. Terahertz-pump second-harmonic-generation(SHG)-probe and optical-reflectivity-probe spectroscopy reveal that the ferroelectric polarization originates from intermolecular charge transfers and is inclined 27° from the horizontal CO stripe. These features are qualitatively reproduced by the density-functional-theory calculation. After sub-picosecond polarization modulation by terahertz fields, prominent oscillations appear in the reflectivity but not in the SHG-probe results, suggesting that the CO is coupled with molecular displacements, while the ferroelectricity is electronic in nature. The results presented here demonstrate that terahertz-pump optical-probe spectroscopy is a powerful tool not only for rapidly controlling polarizations, but also for clarifying the mechanisms of ferroelectricity. Nature Publishing Group 2016-02-11 /pmc/articles/PMC4750076/ /pubmed/26864779 http://dx.doi.org/10.1038/srep20571 Text en Copyright © 2016, Macmillan Publishers Limited http://creativecommons.org/licenses/by/4.0/ This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
spellingShingle Article
Yamakawa, H.
Miyamoto, T.
Morimoto, T.
Yada, H.
Kinoshita, Y.
Sotome, M.
Kida, N.
Yamamoto, K.
Iwano, K.
Matsumoto, Y.
Watanabe, S.
Shimoi, Y.
Suda, M.
Yamamoto, H. M.
Mori, H.
Okamoto, H.
Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy
title Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy
title_full Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy
title_fullStr Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy
title_full_unstemmed Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy
title_short Novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy
title_sort novel electronic ferroelectricity in an organic charge-order insulator investigated with terahertz-pump optical-probe spectroscopy
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4750076/
https://www.ncbi.nlm.nih.gov/pubmed/26864779
http://dx.doi.org/10.1038/srep20571
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