Second harmonic generation as a probe of broken mirror symmetry in a charge density wave transition
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Second harmonic generation as a probe of broken mirror symmetry in a charge density wave transition

  • Author(s): Fichera, Bryan T
  • Kogar, Anshul
  • Ye, Linda
  • Göcke, Bilal
  • Zong, Alfred
  • Checkelsky, Joseph G
  • Gedik, Nuh
  • et al.
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 1$T$-TaS$_2$, we demonstrate here that rotational-anisotropy second harmonic generation (RA-SHG) is a sensitive technique for the detection of broken mirror symmetry. We find that RA-SHG can differentiate between mirror symmetry-broken structures of opposite planar chirality. We are also able to identify a binary indicator of broken mirror symmetry, as well as an indicator of the sense of the planar chirality. Lastly, we find evidence for bulk mirror symmetry-breaking in the incommensurate charge density wave phase of 1$T$-TaS$_2$. Our results pave the way for RA-SHG to probe candidate materials where broken mirror symmetry may play a pivotal role.

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