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—under surprising liquid nitrogen temperature—in RG multilayers from 3 to 9 layers by using scanning tunnelling microscopy and spectroscopy. We explicitly determine layer-enhanced low-energy flat bands and interlayer coupling strengths. The former directly demonstrates the further flattening of low-energy bands in thicker RG, and the latter indicates the presence of varying interlayer interactions in RG multilayers. Moreover, we find significant splittings of the flat bands, ranging from ~50 meV to 80 meV, at 77 K 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 and demonstrate it as a suitable system for investigating robust and highly accessible correlated phases.

最近在三层菱形石墨烯 （RG） 中发现的超导性和磁性为研究强相关电子现象建立了一个理想的、未扭曲的平台。然而，多层 RG 中的相关效应受到的关注有限，特别是，随着层数的增加，相关性的演变仍然是一个未解决的问题。在这里，我们展示了在令人惊讶的液氮温度下，通过使用扫描隧道显微镜和光谱学在 3 至 9 层的 RG 多层中观察层依赖性电子结构和相关性。我们明确确定了层增强的低能平带和层间耦合强度。前者直接表明低能带在较厚的 RG 中进一步变平，而后者表明 RG 多层中存在不同的层间相互作用。此外，我们发现当它们部分填充时，平坦带在 77 K 时出现显着分裂，范围从 ~50 meV 到 80 meV，表明出现了相互作用诱导的强相关状态。特别是，相关态的强度在较厚的 RG 中显著增强，并在六层中达到最大值，直接验证了理论预测并为强相关系统建立了丰富的新候选者。我们的结果为 RG 中电子特性的层依赖性提供了有价值的见解，并证明它是研究稳健且高度可及的相关相的合适系统。