  Many intriguing quantum states of matter, such as unconventional
superconductivity, magnetic phases and fractional quantum Hall physics,
emergent from the spatially-correlated localized electrons in the flat band of
solid materials. By using scanning tunneling microscopy and spectroscopy
(STM/STS), we report the real-space investigation of correlated electrons in
the flat band of superlattice 4Hb-TaSexS2-x. In contrast with the pristine
4Hb-TaS2, the selenium (Se) substitutions significantly affect the interfacial
transfer of correlated electrons between the CDW states of 1T- and 1H-TaS2
layers, and contribute a real-space fractional electron-filling configurations
with the distributed electron-filled and -void SoD clusters of 1T-layer. The
site-specific STS spectra directly reveal their respective prominent spectra
weight above EF and symmetric Mott-like spectra. In addition, the spatial
distributions of these electron-filled SoDs in the 1T-layer of 4Hb-TaSe0.7S1.3
demonstrate different local short-range patterning, clearly indicating the
complex neighboring interactions among the localized electrons in the flat band
of 1T-layer. Our results not only provide an in-depth insight of correlated
electrons in the flat CDW band, and provide a simple platform to manipulate the
electron-correlation-related quantum states.
