Sub-picosecond control of polarized domain in organic ferroelectrics using second harmonic microscope

2018 Fiscal Year Final Research Report

• Project/Area Number: 16H04000
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Condensed matter physics I
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Okimoto Yoichi 東京工業大学, 理学院, 准教授 (50356705)
• Research Collaborator: Horiuchi Sachio 産総研 ; Onda Ken 九大理
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 強誘電体 / 第二次高調波発生 / フェムト秒分光

Outline of Final Research Achievements

Ferroelectric supramolecular cocrystal H6,6dmbp-Hca (H6,6dmbp=protonated 6,6’-dimethyl-2,2’-bipyridinium, Hca = deprotonated chloranilic acid) shows ferroelectricity with high Curie temperature (Tc=380 K). In this study, we focused on H6,6dmbp-Hca and investigated the dynamics of ferroelectric property after photoexcitation in terms of time-resolved nonlinear spectroscopy using fs laser pulses.
We observed ultrafast changes of the second harmonic (SH) intensity after photoexcitation of 530 nm pulse exciting π‐π* transition in Hca molecule. We observed that the cocrystal were composed of two different areas where the SH increases or decreases by ca.10% just after the photoexcitation even on the single crystal of H6,6’dmbp-Hca and that the degree of the photoinduced change could be varied with applying external electric field. These results indicate that the photoinduced change of SH intensity is due to photomodulation of the ferroelectric domains embedded in the cocrystal.

Free Research Field

固体光物性

Academic Significance and Societal Importance of the Research Achievements

本研究の結果から、プロトン移動型有機強誘電体から出る第二次高調波発生強度を、光励起（分子内励起）によりサブピコ秒スケールで制御できること、およびその変化の度合いは試料の分極ドメインの状況を敏感に反映すること、が明らかになった。これは、光照射が強誘電体の分極ドメインを実空間で高速に動かしていることを端的に示すものである。更にこれらの結果は、強誘電体の分極反転を外部電場の代わりに光で高速に行える可能性も示しており、本系をメモリなどに応用する場合にその応答速度を高速化できることが期待できるなどの応用への道を拓くものである。