  (TaSe4)2I, a quasi-one-dimensional (1D) crystal, shows a characteristic
temperature-driven metal-insulator phase transition. Above the charge density
wave (CDW) temperature Tc, (TaSe4)2I has been predicted to harbor a Weyl
semimetal phase. Below Tc, it becomes an axion insulator. Here, we performed
angle-resolved photoemission spectroscopy (ARPES) measurements on the (110)
surface of (TaSe4)2I and observed two sets of Dirac-like energy bands in the
first Brillion zone, which agree well with our first-principles calculations.
Moreover, we found that each Dirac band exhibits an energy splitting of
hundreds of meV under certain circumstances. In combination with core level
measurements, our theoretical analysis showed that this Dirac band splitting is
a result of surface charge polarization due to the loss of surface iodine
atoms. Our findings here shed new light on the interplay between band topology
and CDW order in Peierls compounds and will motivate more studies on
topological properties of strongly correlated quasi-1D materials.
