Understanding Origin of Unexpected Nonlinear Optical Response in TaTe₂

Second Harmonic Generation (SHG) is a nonlinear optical process which has been used to study electronic, lattice, and magnetic properties in non-centrosymmetric materials where inversion symmetry breaks. In this talk, we provide experimental results towards understanding an unexpected observation of strong SHG signal in a transitional metal dichalcogenide Tantalum ditelluride (TaTe₂), which has previously been known as a centrosymmetric bulk crystal preserving C2/m point group with inversion symmetry. We examine the electronic and structural properties of in-situ cleaved bulk TaTe₂ by using synchrotron-based nano-ARPES at Berkeley National Lab and XPEEM/LEEM at Brookhaven National Lab. Our nano-ARPES measurements examined the electronic structure and revealed the exhibition of rotational charge domains on the TaTe₂ surface. Our XPEEM/LEEM measurements further confirmed the interlayer character of the rotations. Our micro-spectroscopic results suggest the creation of inversion symmetry breaking at the interface where the intrinsic interlayer rotations are exhibited in bulk TaTe₂, which could contribute to the SHG signal otherwise forbidden. These results reveal previously hidden rotational degree of freedom in TaTe₂ crystal and its potential optical and electronic consequences.