Charge-parity symmetry observed through Friedel oscillations in chiral charge-density waves

We discovered a chiral behavior of Friedel oscillations (FOs), which have both triangular symmetry and inverse chirality from chiral charge-density waves (CDWs) in 1T-TiSe2 by using scanning tunneling microscopy (STM). Surprisingly, the existence of FOs with the opposite chirality to the underlying CDWs suggests that the excess electron induced by impurity reduces the local helicity of CDWs without CDW breaking. This FOs can be explained with a two-branch model with different chiralities, which permits excitation from one branch to another, that is, Dirac-type dispersion. Moreover, we found two states that correspond to electron addition and electron removal. In terms of the chirality of electrons, these two states are the same. This result provides an evidence for the charge-parity (CP) symmetry conservation in CDW systems.