Sub-Nanometer Sensitivity of Laser-Driven Phase Transitions in Semiconductors

Jhih-Jia Chen^1*, Te-Hsin Yen¹, Kentaro Nishida¹, Junichi Takahara², Shi-Wei Chu^1,3,4

¹Department of Physics, National Taiwan University, Taipei, Taiwan
²Graduate School of Engineering, Osaka University, Osaka, Japan
³Molecular Imaging Center, National Taiwan University, Taipei, Taiwan
⁴Brain Research Center, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Jhih-Jia Chen, email:f12222001chen@gmail.com

Metasurfaces offer a compact platform for nanoscale light manipulation, and the integration of phase-change materials (PCMs) introduces tunability for applications such as beam steering, image processing, and optical switching. While most demonstrations rely on global PCM switching, localized control is accomplished by inducing phase transitions in individual meta-atoms through focused laser excitation. This strategy enables direct encoding of optical amplitude and phase via distinct material states, extending the design space beyond conventional structural parameters such as geometry, height, or orientation. However, the role of excitation beam position relative to the nanostructure remains largely unexplored. Following our recent discovery of displacement resonance (Nat. Comm 14, 7213 (2023)), here we demonstrate that phase transitions in silicon nanostructures exhibit sub-nanometer spatial controllability, i.e. crystalline/amorphous phase change is switched on/off with beam displacement as small as 0.5 nm. The spatial sensitivity is invariant with respect to nanostructure size and excitation wavelength, while the transition threshold follows the absorption spectrum. These findings reveal a new degree of spatial precision in optical phase-change control and underpin the potential of beam-position engineering for reliable and reconfigurable nanophotonic applications.

Keywords: silicon, nanostructure, phase change, Mie resonance