Unraveling SSPM Phenomena in Type-II Dirac Semimetal NiTe₂ for All-Optical Diodes and Switching Applications

The tilted Dirac cones in the type-II Dirac semimetal NiTe₂ enhance charge transport efficiency, leading to strong optical absorption and a significant nonlinear optical response. This pronounced nonlinear optical behavior in NiTe2 is confirmed by the large nonlinear susceptibility (≈10⁻⁷ esu) observed herein for red, green, and violet lasers. Furthermore, the theoretically calculated value of χ⁽³⁾ using semi-empirical Miller's rule predicted its value≈1.12 × 10^-7 esu, tallying well with the experimentally observed results. These findings suggest that NiTe₂ exhibits a nonlinear optical response comparable to that of graphene. The large χ⁽³⁾ value is attributed to laser-induced carrier coherence, facilitated by the high Dirac carrier mobility. The formation of diffraction rings is explained using the Wind-Chime model, with measured ring formation times of 0.64, 0.32, and 0.64 s for red (672 nm), green (532 nm), and violet (405 nm) lasers, respectively. The Wind-Chime model is further validated using solvents with varying viscosity and polarity (polar and nonpolar), showing strong agreement with the experimental results. Additionally, an optical diode based on NiTe₂ combined with V₂O₅ and CeO₂ is demonstrated, along with an all-optical OR logic gate, highlighting NiTe₂ as a promising candidate for photonic device applications.