A 2D van der Waals Terahertz Emitter with Giant Optical Rectification

Exfoliation and stacking of two-dimensional (2D) van der Waals (vdW) crystals have created unprecedented opportunities in the discovery of quantum phases. A major obstacle to the advancement of this field is the limited spectroscopic access due to a mismatch in sample sizes (10^−6 – 10^−5 m) and wavelengths (10^−4 – 10^−3 m) of electromagnetic radiation relevant to their low-energy landscape and excitations. Here, we introduce a new member of the 2D vdW material family: a terahertz (THz) emitter. We show intense and broadband THz generation from a vdW polar semiconductor with optical rectification efficiency over one order of magnitude higher than that of the current standard THz emitter, ZnTe. The THz emitter can be easily integrated into vdW heterostructures for on-chip near-field THz spectroscopy of a target vdW material/device. Our approach provides a general spectroscopic tool for the rapidly expanding field of 2D vdW materials and quantum matter.