Origin of the Efficient Nonlinear Optical Response of Two-Dimensional Layered CuFeTe₂ Nanosheets

Two-dimensional ternary transition metal chalcogenides (TMCs) have aroused great research interest owing to outstanding semiconducting properties and diverse magnetic response. CuFeTe₂, as a typical TMC, exhibits ambiguous magnetic behavior and ground state of spin density waves nature. Herein, we first report efficient nonlinear absorption and superior nonlinear refraction of CuFeTe₂ nanosheets. The nonlinear absorption and refraction coefficients reach -0.22 cm/GW and -1.66 × 10^-12 cm²/W, respectively. Semiempirical theory for direct bandgap semiconductors was applied to estimate the nonlinearities of CuFeTe₂ nanosheets. The calculation results indicate that the efficient nonlinearities stem from the free carrier induced band filling effect.