Coupled Spin and Orbital Magnetism in ABC Trilayer Graphene

ABC trilayer graphene under an applied perpendicular electric field hosts a van Hove singularity that can be accessed by field-effect doping, where a variety of spin and valley symmetry breaking ferromagnetic phases have been observed. Among these are a ‘quarter metal’ phase, where quantum oscillations show the existence of a single Fermi surface [1]. Using both tilted-magnetic field transport, capacitance, and nanoSQUID on Tip (nSOT) microscopy, I will show that the quarter metal regime actually hosts two distinct phases, separated by a first order phase transition and distinguished by different orbital and spin magnetic moments. Surprisingly, the orbital magnetic moment of one of these phases can be tuned by an in-plane magnetic field, implying that the orbital motion is coupled to the electron spin despite the lack of atomic spin orbit coupling. I will discuss our results in the context of novel mechanisms for emergent spin orbit coupling arising from the interplay of Coulomb interactions, spin textures, and orbital magnetism [2].