where X(k) + is the exciton character and C(k) + is the photonic character of the |+⟩ state. 131 Note that for Fabry-Pérot cavities, ω k is polarization independent, so typically only the TM mode is considered. We emphasize that for a plasmonic cavity, Eq. 87 no longer always holds. For example, the plasmonic cavity 133,134 has a similar dispersion for the TM polarization ω k,TM = c n eff k 2