Speaker: Dr. Leo Li, Brown University
Abstract: The low-temperature phase diagram of multi-layer graphene offers an ideal venue to investigate the complex interplay between Coulomb interaction, broken symmetries, and nontrivial band topology. For instance, recent theoretical predictions shed light on a new type of Coulomb-driven instability in the momentum space of bilayer graphene, which breaks rotational and time-reversal symmetry simultaneously. Here, I utilize the angle-resolved measurement of transport nonreciprocity to examine the nature of spontaneous symmetry breaking in multi-layer graphene. By analyzing the angular dependence of nonreciprocity in both longitudinal and transverse channels, we directly identify the mirror plane of the underlying electronic order, which offers unambiguous evidence for spontaneous in-plane rotational symmetry breaking. By investigating the interplay between transport nonreciprocity, ferromagnetism, and superconductivity, we uncover a direct link between spontaneous breaking of rotational and time-reversal symmetry in multi-layer graphene. Combined, our findings suggest that the exchange-driven instability in the momentum space plays a key role in defining the landscape of emergent phenomena in multilayer graphene.