Second harmonic generation as a probe of broken mirror symmetry
Bryan T. Fichera, Anshul Kogar, Linda Ye, Bilal Gökce, Alfred Zong, J. G. Checkelsky, Nuh Gedik
Abstract
The notion of spontaneous symmetry breaking has been used to describe phase transitions in a variety of physical systems. In crystalline solids, the breaking of certain symmetries, such as mirror symmetry, is difficult to detect unambiguously. Using $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, we demonstrate here that rotational-anisotropy second harmonic generation (RA-SHG) is not only a sensitive technique for the detection of broken mirror symmetry, but also that it can differentiate between mirror symmetry-broken structures of opposite planar chirality. We also show that our analysis is applicable to a wide class of different materials with mirror symmetry-breaking transitions. Lastly, we find evidence for bulk mirror symmetry-breaking in the incommensurate charge density wave phase of $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$. Our results pave the way for RA-SHG to probe candidate materials where broken mirror symmetry may play a pivotal role.