In a groundbreaking advancement that is poised to revolutionize the field of nonlinear optics and electroplasmonics, researchers from the Institute for Molecular Science (IMS) in Japan, together with SOKENDAI, have unveiled an angstrom-scale electroplasmonic platform capable of inducing an unprecedented giant modulation of near-field nonlinear optical effects. This pioneering discovery enables a modulation depth exceeding 2000% per volt, a feat that dramatically surpasses previous benchmarks by over two orders of magnitude, and opens new horizons for ultracompact electrophotonic devices that operate on atomic length scales.
At the heart of this breakthrough lies the manipulation of the plasmonic nanogap formed between a metallic gold (Au) tip and substrate within a scanning tunneling microscope (STM) system. The angstrom-scale dimension of this gap—on the order of one-tenth of a nanometer—permits extreme confinement of electromagnetic fields, which is unattainable in conventional plasmonic arrangements characterized by tens to hundreds of nanometers. The researchers utilized this ultra-small gap to generate stimulated second-harmonic generation (SHG) signals that could be modulated by varying the voltage across the junction by only ±1 volt, yielding a quadratic dependence of SHG intensity on the applied bias.
This extraordinary voltage-tunable response arises from the immense electrostatic fields established inside the gap, which are on the order of 10⁹ volts per meter due to the inverse scaling of field strength with gap distance. Such colossal fields have a profound effect on the electronic states of molecules situated within the gap, dynamically altering their nonlinear optical susceptibilities. Unlike traditional plasmonic architectures where the applied fields are significantly weaker, this angstrom-scale metal junction creates an environment conducive to highly efficient and tunable nonlinear light-matter interactions.
Further extending the versatility of this platform, the team observed similar giant electrical modulation in sum-frequency generation (SFG) processes, which facilitate the up-conversion of mid-infrared photons into visible or near-infrared light. This finding highlights the tunability’s broadband nature and its applicability beyond a single nonlinear optical phenomenon or wavelength regime. Such flexibility is critical for future applications that demand multispectral control over light emission and conversion at the nanoscale.
This research not only elucidates the mechanisms underlying the voltage-controlled enhancement of nonlinear optical processes but also establishes a new paradigm for miniaturization in electro-optical devices. The angstrom-scale plasmonic junction represents an unprecedented technological platform where electrical and optical signals can be interfaced and manipulated simultaneously within a spatial domain reduced to the ultimate atomic scale.
Key to the implementation of this technology is the precision employed in constructing and stabilizing the STM junction, involving a gold tip delicately positioned over a gold substrate. The femtosecond near-infrared laser irradiation at fundamental frequency ω excites plasmonic resonances within the nanogap, while the resulting SHG at 2ω is detected with high sensitivity. This experimental setup leverages the synergy between scanning probe microscopy and nonlinear optics, offering unprecedented spatial and spectral resolution.
The implications of such efficient voltage-driven modulation are far-reaching. By achieving extremely high modulation depths, the electromodulation of nonlinear optical signals can significantly reduce the energy consumption in electro-photonic circuits. This is especially crucial for the ongoing miniaturization trends in photonics, where device footprints and power requirements must simultaneously shrink while maintaining, or even enhancing, performance.
Dr. Shota Takahashi, the lead author and assistant professor at IMS, emphasizes the transformative potential of this discovery. He notes that the ability to electrically govern nonlinear light generation with such precision and depth at angstrom scales could catalyze the development of the next generation of ultracompact electro-photonic devices. These devices may seamlessly interconvert electrical and optical information at scales far beyond the reach of current technologies, heralding new avenues in data processing and communication.
Looking ahead, the research team plans to explore materials exhibiting even stronger electric-field responsiveness to push the boundaries of modulation depth further. Parallel efforts aim to develop robust theoretical frameworks capable of quantitatively predicting electrical modulation effects in angstrom-scale junctions. Such models are paramount for transferring this technological innovation into practical devices and for extending it across diverse scientific disciplines.
The synergy of nonlinear optics, nanophotonics, condensed matter physics, and electronic engineering realized in this work underscores the multidisciplinary essence of modern scientific innovation. By harnessing ultra-confined electrostatic fields, the researchers have successfully bridged the gap between atomic-scale electronic manipulation and macroscopic optical phenomena, demonstrating a paradigm shift in the control of light.
In conclusion, the angstrom-scale plasmonic junction pioneered by the IMS team exemplifies the profound impact that nanoscale engineering can have on the fundamental understanding and application of nonlinear optical processes. This innovation sets a new standard for voltage-induced modulation efficiencies and paves the way not only for ultra-efficient electrophotonic devices but also for a deeper understanding of light-matter interactions at the smallest conceivable scales.
Subject of Research: Not applicable
Article Title: Giant near-field nonlinear electrophotonic effects in an angstrom-scale plasmonic junction
News Publication Date: 24-Jan-2026
Web References: 10.1038/s41467-026-68823-4
Image Credits: Adapted from Takahashi et al. (2026), Nature Communications
Keywords
Nonlinear Optics, Electroplasmonics, Angstrom-Scale Gap, Scanning Tunneling Microscope, Second-Harmonic Generation, Sum-Frequency Generation, Ultrafast Laser, Electro-Optical Modulation, Nanophotonics, Atomic-Scale Electronics, Plasmonics, Electro-Photonic Devices
