Strain-Driven Symmetry Breaking and Enhanced SHG in Centrosymmetric 1T-PtS₂

Second-harmonic generation (SHG) in two-dimensional (2D) materials typically requires broken inversion symmetry, posing a fundamental constraint for nonlinear optical applications. Surprisingly, the SHG phenomenon was recently observed in centrosymmetric 1T-phase transition metal disulfide compounds (1T-TMDs), but its underlying mechanism and tunability remain elusive. Here, taking the centrosymmetric 1T-PtS₂ as an example, we investigate the SHG responses and origin, finding a surprising giant SHG response, exhibiting intensities up to 15 times greater than noncentrosymmetric monolayer WS₂ under the same excitation conditions. This is attributed to the sensitive response of SHG in 1T-PtS₂ to tiny strain introduced by mechanical exfoliation, which is confirmed by the anisotropic six-petal polarization pattern. By engineering a controlled strain environment using patterned Au pillars and Si hole arrays, we enhanced the SHG signal by a factor of 3, further indicating exceptional strain sensitivity of the 1T phase. Theoretical calculations reveal that strain disrupts lattice symmetry and disturbs uniform charge distribution of 1T-PtS₂, which induces the SHG. Our results provide new insights into central symmetry structure-induced second harmonics and establish a foundation for developing the next generation of open functional SHG devices.