Charge Density Wave Induced Second-Harmonic Generation in 1T-TaSe₂

Charge density wave (CDW) is ordered states characterized by periodic modulation of charge density and accompanying lattice distortions, often leading to superlattice formation and modified electron-phonon coupling. While CDW formation has been extensively studied, its impact on nonlinear optical coefficients remains largely unexplored. Here we report a pronounced second-harmonic generation (SHG) response in centrosymmetric 1T-TaSe₂, whose intensity is nearly 20 times that of the 2H phase and exhibits distinct polarization dependence. Temperature-dependent transient absorption spectroscopy reveals a characteristic CDW phonon mode at ~1.88 THz at 463 K, which progressively redshifts and broadens with increasing temperature. Further corroboration was provided by complementary temperature-dependent SHG measurements and corresponding Raman spectroscopic analyses. These findings collectively demonstrate that the inversion symmetry breaking induced by CDW-related lattice distortions is the primary origin of the SHG response observed in 1T-TaSe₂. This study reveals that controlling the formation of CDW superlattices through temperature modulation provides an effective avenue for tuning nonlinear optical responses, thereby offering a novel strategy for the rational design of nonlinear optical materials.