Abstract: Within the flat energy bands of multilayer graphene, the enhanced influence of Coulomb interaction is reflected by the emergence of exchange-driven instabilities, which stabilize isospin-ordered phases by lifting the spin and valley degeneracy. These isospin-ordered phases are ubiquitous in the low-temperature phase space of multilayer graphene, having been observed in Bernal bilayer, rhombohedral trilayer, and a number of twisted graphene heterostructures near the magic-angle. Here, I will discuss a new type of Coulomb-driven instability that is driven by the exchange interaction between trigonal-warping-induced Fermi pockets. It is recently proposed that such instability could induce a spontaneous condensation of charge carriers into one of the Fermi pockets, giving rise to a net polarization in the momentum space. Such exchange-driven instability can be directly probed and characterized using angle-resolved nonlinear transport measurement at the second-harmonic frequency. Beyond the experimental identification of momentum polarization, I will discuss its implication on our understanding of electronic orders in the flat energy band of multilayer graphene.