  The recent discovery of superconductivity and magnetism in trilayer
rhombohedral graphene (RG) establishes an ideal, untwisted platform to study
strong correlation electronic phenomena. However, the correlated effects in
multilayer RG have received limited attention, and, particularly, the evolution
of the correlations with increasing layer number remains an unresolved
question. Here, we show the observation of layer-dependent electronic
structures and correlations in RG multilayers from 3 to 9 layers by using
scanning tunneling microscopy and spectroscopy. We explicitly determine
layer-enhanced low-energy flat bands and interlayer coupling strength. The
former directly demonstrates the further flattening of low-energy bands in
thicker RG, and the later indicates the presence of varying interlayer
interactions in RG multilayers. Moreover, we find significant splitting of the
flat bands, ranging from ~50-80 meV, under liquid nitrogen temperature when
they are partially filled, indicating the emergence of interaction-induced
strongly correlated states. Particularly, the strength of the correlated states
is notably enhanced in thicker RG and reaches its maximum in the six-layer,
validating directly theoretical predictions and establishing abundant new
candidates for strongly correlated systems. Our results provide valuable
insights into the layer dependence of the electronic properties in RG, paving
the way for investigating robust and highly accessible correlated phases in
simpler systems.
