Optical second harmonic generation in WTe2

We study second harmonic generation (SHG) in an acentric Weyl semimetal, tungsten ditelluride (WTe2), and estimate its second-order electric susceptibility, χ(2). WTe2 is a layered material that has a natural cleavage plane perpendicular to the c-axis, but the crystal symmetry prohibits SHG emission when light is normally incident on the natural planar surface. Hence, we measure the SHG susceptibility in a laser scanning microscope, where it is easier to measure the SHG from the striated edges of the crystal. We determine the susceptibility from the variation of the SHG images with incident power, using a model that accounts for both the statistics of the SHG detection process and the surface inhomogeneities of the sample. A preliminary estimate shows that χ(2) in WTe2 is comparable to that of GaAs, a well studied nonlinear crystal with large second-order susceptibility.