Journal Article terahertz phase discontinuities Research Support, Non-U.S. Gov't coherent control diffraction metamaterials Metals Metasurfaces Pancharatnam-Berry phase optical element Review THz metasurface Vanadium dioxide asymmetric transmissions broadband broadband terahertz generation chirality complete control coupling‐controlled chiral meta‐atom dielectric dynamic metasurface geometric phase metagratings metasurfaces near-field microscopy nonlinear metasurfaces non‐interleave phase change material refraction surface waves