Rotational-Anisotropy Nonlinear Harmonic Generation Study of the Charge Density Wave Phase of 1T-TiSe₂

The charge density wave (CDW) phase of the transition metal dichalcogenide 1T-TiSe₂ features a non-trivial symmetry configuration at T_CDW ≈ 200 K, with varying interpretations on the existence of a chiral CDW state that putatively onsets ~10 K below T_CDW. The nonlinear optical technique of rotational anisotropy-nonlinear harmonic generation (RA-NHG), in which the n^th harmonic of an incident laser field is measured as a function of incoming and outgoing polarization, can reveal symmetry changes deriving from the lattice, charges, and spins that may be less obvious from conventional scattering probes. Here, we present a RA-NHG study of 1T-TiSe₂ as a function of temperature and wavelength, and discuss how our findings relate to the debate on the existence of a chiral CDW in this material.