Online Information for “ Chiral plasmons without magnetic field ”

For a complementary view to the approach employed in the main text, here we present an alternative formulation of the plasmon equations of motion. Rather than focusing on the semiclassical equations of motion for the particle and velocity density fields, here we work with the charge density ρ(r, t) = −en(r, t), the current density j(r, t), and the conductivity tensor σ. As we will be interested in oscillatory collective (plasmon) modes, it will be useful to work in terms of Fourier modes, ρ(r, t) = ρω(r)e , j(r, t) = jω(r)e , and φ(r, t) = φω(r)e . The charge and current densities obey a continuity equation, which in terms of the Fourier modes reads: