  In unconventional high-temperature (high-Tc) superconductors, the
symmetry-breaking electronic orders intertwined with the superconductivity
provide important clues for understanding the nature of the unconventional
pairing mechanism. Recently, an exotic superconducting order showing spatially
periodic order parameter modulations and translational symmetry breaking,
namely the pair density wave (PDW) state, has attracted broad attention.
Without breaking translational symmetry, point group symmetry breaking may also
induce superconductivity modulations on different atom sites within a single
unit cell. However, the intra-unit-cell superconductivity modulation has never
been carefully investigated before. Here, using scanning tunneling
microscopy/spectroscopy, we report the observation of intra-unit-cell
superconductivity modulations in the superconducting gap size and the coherence
peak sharpness in monolayer high-Tc Fe(Te,Se) films epitaxially grown on
SrTiO3(001) substrates. Further analysis shows that the maxima and minima in
the superconductivity modulation are centered at the crystallographic locations
of the Te/Se atoms, revealing the breaking of the glide-mirror symmetry of the
Te/Se atoms in monolayer high-Tc Fe(Te,Se) films grown on SrTiO3(001). Our
findings provide precise microscopic information of superconductivity within
the lattice unit cell and indicate that the p-orbital electrons of the Te/Se
atoms also play an important role in Cooper pairing in unconventional high-Tc
iron-based superconductors.
