IUPAP Award Talk

Most ferromagnets are based on the polarizatoin of electron spins. However, ferromagnetism based on purely orbital degrees of freedom is also possible, though experimental examples are rare. In this talk I will describe recent experiments that explore the proliferation of orbital magnets in graphene based systems. Most simply, I will show that in rhombohedral trilayer graphene at low density, the electron gas takes advantage of the intrinsic valley degree of freedom to form an itinerant orbital magnet. In systems with a moire potential, including rhombohedral trilayer aligned to hBN as well as a variety of rotationally faulted graphene systems, the moire superlattice allows for electronic gaps to form at finite electron densities corresponding to integer or fractional filling of the moire band. Among these are spontaneous Chern insulators---gapped ferromagnetic showing quantized Hall conductivity at zero magnetic field. I will discuss new phenomena observed in these unusual magnets in a variety of moire systems, including electrically actuated switching of magnetic states using current- and gate voltage and the observation of Chern insulators that spontaneously break the superlattice symmetry.