Unraveling SSPM Phenomena in Type‐II Dirac Semimetal NiTe ₂ for All‐Optical Diodes and Switching Applications

Abstract The tilted Dirac cones in the type‐II Dirac semimetal NiTe ₂ 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 NiTe ₂ 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 NiTe ₂ combined with V₂O₅ and CeO ₂ is demonstrated, along with an all‐optical OR logic gate, highlighting NiTe ₂ as a promising candidate for photonic device applications.