Tang Tianhong, Hu Deng, Lin Di, Yang Liu, Shen Ziling, Yang Wenchen, Liu Haiyang, Li Hanting, Fan Xiaoyue, Wang Zhiwei, Wang Gang
Centre for Quantum Physics, Key Laboratory of Advanced Optoelectronic Quantum Architecture and Measurement (MOE), School of Physics, Beijing Institute of Technology, Beijing 100081, China.
Beijing Key Lab of Nanophotonics and Ultrafine Optoelectronic Systems, Beijing Institute of Technology, Beijing 100081, China.
Nanomaterials (Basel). 2024 Feb 23;14(5):412. doi: 10.3390/nano14050412.
The niobium oxide dihalides have recently been identified as a new class of van der Waals materials exhibiting exceptionally large second-order nonlinear optical responses and robust in-plane ferroelectricity. In contrast to second-order nonlinear processes, third-order optical nonlinearities can arise irrespective of whether a crystal lattice is centrosymmetric. Here, we report third harmonic generation (THG) in two-dimensional (2D) transition metal oxide iodides, namely NbOI and TaOI. We observe a comparable THG intensity from both materials. By benchmarking against THG from monolayer WS, we deduce that the third-order susceptibility is approximately on the same order. THG resonances are revealed at different excitation wavelengths, likely due to enhancement by excitonic states and band edge resonances. The THG intensity increases for material thicknesses up to 30 nm, owing to weak interlayer coupling. After this threshold, it shows saturation or a decrease, due to optical interference effects. Our results establish niobium and tantalum oxide iodides as promising 2D materials for third-order nonlinear optics, with intrinsic in-plane ferroelectricity and thickness-tunable nonlinear efficiency.
氧化铌二卤化物最近被认定为一类新型范德华材料，具有异常大的二阶非线性光学响应和稳健的面内铁电性。与二阶非线性过程不同，三阶光学非线性无论晶格是否为中心对称均可产生。在此，我们报道了二维（2D）过渡金属氧化物碘化物（即NbOI和TaOI）中的三次谐波产生（THG）。我们观察到这两种材料的THG强度相当。通过与单层WS的THG进行基准比较，我们推断三阶极化率大致处于同一量级。在不同的激发波长下揭示了THG共振，这可能是由于激子态和带边共振的增强所致。由于层间耦合较弱，THG强度在材料厚度达到30 nm之前会增加。超过这个阈值后，由于光学干涉效应，它会出现饱和或下降。我们的结果表明，氧化铌和氧化钽碘化物是用于三阶非线性光学的有前景的二维材料，具有固有的面内铁电性和厚度可调的非线性效率。
