2026, Strain-controlled polar-ion displacement unlocks reconfigurable second-harmonic generation in van der Waals CuCrP₂S₆ , ACS Photonics.

Abstract:

Two-dimensional van der Waals multiferroics offer a low-dimensional platform for tuning nonlinear optical responses through lattice distortion and polar symmetry. Yet translating polar-ion displacement into strong and tunable macroscopic second-harmonic generation (SHG) remains challenging, as limited ionic off-centering and interlayer cancellation suppress the effective nonlinear polarization. Here we show that local strain enables strongly reconfigurable nonlinear optical responses in CuCrP₂S₆ by amplifying polar Cu⁺ displacement. Thickness-dependent measurements reveal nonmonotonic SHG, indicating incomplete interlayer polarization compensation. Strain-enhanced Cu⁺ displacement strengthens SHG, while Au-induced near fields provide additional amplification and reorient the polarization axis. Temperature-dependent SHG exhibits a nonmonotonic evolution across 140–150 K, consistent with Cu⁺-related structural evolution and low-temperature antipolar compensation. Theoretical calculations reveal that strain induces Cu-site reconstruction and charge redistribution, providing microscopic insight into the structural mechanism underlying strain-modulated SHG response. These results establish strain controlled ionic displacement as a microscopic route to tunable nonlinear optics in multiferroics.

Keywords: Nonlinear optics, Multiferroicity, Inversion-symmetry breaking, Local structural reconstruction, Theoretical calculations

Link: https://pubs.acs.org/apchd5/article/doi/10.1021/acsphotonics.6c01675/5427469/Strain-Controlled-Polar-Ion-Displacement-Unlocks?guestAccessKey=81c59312-dfdc-426a-9e19-8e099650ffe5

acsphotonics.6c01675.pdf