Topological plasmonics and out-of-equilibrium plasmonic ferromagnetism
A Pitt/CMU Colloquium
Abstract: Plasmons, the self-sustained collective density modes in metals, form an integral part of the description of interacting electronic systems. Conventionally, plasmon dynamics are often dominated by the density and effective mass of carriers in its host metal. We will discuss how this description falls short in topological materials where the intricate twisting of wavefunctions (i.e. Bloch band quantum geometry) lead to a new class of plasmonic collective modes. These "topological plasmons" possess a wealth of exotic properties such as chirality even in the absence of magnetic field (in anomalous Hall metals), hyperbolic dispersions (in the Fermi arcs of Weyl semimetals), as well as enhanced lifetimes (in topological edge states).
Strikingly, when these wavefunction sensitive plasmons are driven out-of-equilibrium they can even exhibit dynamical symmetry breaking. As an example, we argue that when a non-magnetic metal (such as graphene) is driven by a linearly polarized (achiral) driving field, strong ac fields can enable the plasmons to spontaneously magnetize (acquire chirality). This out-of-equilibrium ferromagnetic phase is supported by "Berryogenesis": the spontaneous generation of a self-induced Bloch band Berry flux that supports and is sustained by a circulating plasmonic motion. These new plasmonic behaviors dramatically expand the phenomenology of interacting (quantum geometric) metals.