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We discovered the chirality of charge-density waves (CDW) in 1T-TiSe₂ by using STM and time-domain optical polarimetry. We found that the CDW intensity becomes Ia₁: Ia₂: Ia₃=1: 0. 70. 1: 0. 50. 1, where Ia₈ (i=1, 2, 3) is the amplitude of the tunneling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease clockwise and anticlockwise. The chirality in CDW results in the threefold symmetry breaking. Macroscopically, twofold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality H₂₃ₖq₁ (q₂q₃), where q₈ are the CDW q vectors, which is independent of the symmetry of components. The nonzero H₂₃ₖ---the triple-q vectors do not exist in an identical plane in the reciprocal space---should induce a real-space chirality in CDW system.
Ishioka et al. (Mon,) studied this question.