2026-02-02 分子科学研究所
図 1 a. SHG過程のエネルギーダイアグラム。物質に周波数ωを持つ強い光を入射すると、その2倍の周波数(2ω)を持つSHG光が発生する。b. STM装置に設置した金探針の先端の拡大写真。先端の曲率半径は約50ナノメートルと非常に鋭くなっている。c. SHG実験の模式図。近赤外光のフェムト秒パルスレーザーをSTMのナノギャップに照射し、その光を近接場として局在・増強させることで、ギャップ中に存在する分子からのSHG光を検出する。本研究では、探針と基板の間に印加する電圧Vの影響を調べた。
＜関連情報＞
オングストロームスケールのプラズモニック接合における巨大な近接場非線形電気光学効果 Giant near-field nonlinear electrophotonic effects in an angstrom-scale plasmonic junction
Shota Takahashi,Atsunori Sakurai,Tatsuto Mochizuki & Toshiki Sugimoto
Nature Communications Published:24 January 2026
DOI:https://doi.org/10.1038/s41467-026-68823-4
We are providing an unedited version of this manuscript to give early access to its findings. Before final publication, the manuscript will undergo further editing. Please note there may be errors present which affect the content, and all legal disclaimers apply.
Abstract
Plasmons facilitate a strong confinement and enhancement of near-field light, offering exciting opportunities to enhance nonlinear optical responses at the nanoscale. However, despite significant advancements, the electrically tunable range of the nonlinear optical responses at nanometer-scale plasmonic structures remains limited to a few percents per volt. Here, we transcend the limitation of the nanometer regime by expanding the concept of electrophotonics into angstrom-scale platform, enabling high-performance modulation of near-field nonlinear optical responses inaccessible in prior architectures. We demonstrate ~2000% enhancement in second-harmonic generation (SHG) within 1 V of voltage application by utilizing an angstrom-scale plasmonic gap between a metallic tip and a flat metal substrate in a scanning tunneling microscope. Extending this near-field SHG scheme to sum-frequency generation that is accompanied by large frequency upconversion, we also found that such giant electrical modulation of plasmon-enhanced nonlinear optical phenomena is effective over mid-infrared to visible broad wavelength range. Our results and concepts lay the foundation for developing near-field-based angstrom-scale nonlinear electrophotonics with significant modulation depth at low driving voltage.
