Giant and Anisotropic Nonlinear Optical Responses of 1D van der Waals Material Tellurium

Recently, tellurium (Te), composed of helical Te chains stacked via the van der Waals interaction, emerges as a versatile material with high carrier mobilities and intriguing topological properties. Here, it is revealed that Te's 1D counterpart, that is, Te nanowire (NW), has advantages over the NWs of other materials in the characteristics of giant and anisotropic nonlinear optical responses. This endows the Te NW with potentials for developing nonlinear photonic and optoelectronic nanodevices with high efficiency and polarization selectivity. Compared with the well‐studied III–V and II–VI compound NWs, such as aluminium gallium arsenide, zinc oxide, and indium phosphide NWs, second harmonic generations (SHGs) and third harmonic generations (THGs) from the Te NWs are more than two orders of magnitude stronger. Its second‐order nonlinear susceptibility is estimated as 1.25 × 10 4 pm V −1 , which is the highest value in the reported NWs, and almost four orders of magnitude higher than ZnO NW. Further, this giant optical nonlinearity promises the realizations of strong SHGs and sum‐frequency generations from Te NWs with the pump of sub‐milliwatt continuous‐wave lasers. Determined by the helical Te chain, its SHG only responds to the pump laser polarized perpendicularly to the long axis of NW, which is opposite to the polarization dependencies in other NWs, and the THG has a distorted fourfold polarimetric pattern.