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Rhombohedral stacked multilayer graphene is an ideal platform to search forcorrelated electron phenomena, due to its pair of flat bands touching at zeroenergy and further tunability by an electric field. Furthermore, itsvalley-dependent Berry phase at zero energy points to possible topologicalstates when the pseudospin symmetry is broken by electron correlation. However,experimental explorations of these opportunities are very limited so far, dueto a lack of devices with optimized layer numbers and configurations. Here wepresent electron transport measurements of hBN-encapsulated pentalayer grapheneat down to 100 milli-Kelvin. We observed a correlated insulating state with>MOhm resistance at zero charge density and zero displacement field, where thetight-binding calculation predicts a metallic ground state. By increasing thedisplacement field, we observed a Chern insulator state with C = -5 and twoother states with C = -3 at a low magnetic field of ~1 Tesla. At highdisplacement fields and charge densities, we observed isospin-polarizedquarter- and half-metals. Therefore, rhombohedral-stacked pentalayer grapheneis the first graphene system to exhibit two different types of Fermi-surfaceinstabilities: driven by a pair of flat bands touching at zero energy, and bythe Stoner mechanism in a single flat band. Our results demonstrate a newdirection to explore intertwined electron correlation and topology phenomena innatural graphitic materials without the need of moir\'e superlatticeengineering.

Correlated Insulator and Chern Insulators in Pentalayer Rhombohedral Stacked Graphene