  Symmetry-breaking electronic phase in unconventional high-temperature
(high-Tc) superconductors is a fascinating issue in condensed-matter physics,
among which the most attractive phases are charge density wave (CDW) phase with
four unit-cell periodicity in cuprates and nematic phase breaking the C4
rotational symmetry in iron-based superconductors (FeSCs). Recently, pair
density wave (PDW), an exotic superconducting phase with non-zero momentum
Cooper pairs, has been observed in high-Tc cuprates and the monolayer FeSC.
However, the interplay between the CDW, PDW and nematic phase remains to be
explored. Here, using scanning tunneling microscopy/spectroscopy, we detected
commensurate CDW and CDW-induced PDW orders with the same period of lambda =
4aFe (aFe is the distance between neighboring Fe atoms) in a monolayer high-Tc
Fe(Te,Se) film grown on SrTiO3(001) substrate. Further analyses demonstrate the
observed CDW is a smectic order, which breaks both translation and C4
rotational symmetry. Moreover, the smecticity of the CDW order is strongest
near the superconducting gap but weakens near defects and in an applied
magnetic field, indicating the interplay between the smectic CDW and PDW
orders. Our works provide a new platform to study the intertwined orders and
their interactions in high-Tc superconductors.
