So-Young Pi

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Projecting a non-Abelian SU (2) vacuum gauge field – a pure gauge constructed from the group element U – onto a fixed (electromagnetic) direction in isospace gives rise to a nontrivial magnetic field, with nonvanishing magnetic helicity, which coincides with the winding number of U. Although the helicity is not conserved under Maxwell (vacuum) evolution, it(More)
We show that in a large class of physically interesting systems the mass-generation phenomenon can be understood in terms of topological structures, without requiring a detailed knowledge of the underlying dynamics. This is first demonstrated by showing that Schwinger's mechanism for mass generation relies on topological structures of a two-dimensional(More)
Fermion-number fractionalization without breaking the time-reversal symmetry was recently demonstrated for a field theory in ͑2+1͒-dimensional space and time that describes the couplings between massive Dirac fermions, a complex-valued Higgs field carrying an axial gauge charge of 2, and a U͑1͒ axial gauge field. Charge fractionalization occurs whenever the(More)
Controlling the properties of materials by driving them out of equilibrium is an exciting prospect that has only recently begun to be explored. In this Letter we give a striking theoretical example of such materials design: a tunable gap in monolayer graphene is generated by exciting a particular optical phonon. We show that the system reaches a steady(More)