Projection-Reduction Approach to Optical Conductivities for an Electron-Phonon System and Their Diagram Representation

Figure 6

Schematic diagrams of the energy denominators in (a) 𝜎^{(𝐼𝐼𝐼−1)}_{𝑘𝑙𝑚𝑛}(𝜔₁,𝜔₂,𝜔₃), (b) 𝜎^{(𝐼𝐼𝐼−2)}_{𝑘𝑙𝑚𝑛}(𝜔₁,𝜔₂,𝜔₃), (c) 𝜎^{(𝐼𝐼𝐼−3)}_{𝑘𝑙𝑚𝑛}(𝜔₁,𝜔₂,𝜔₃), and (d) 𝜎^{(𝐼𝐼𝐼−4)}_{𝑘𝑙𝑚𝑛}(𝜔₁,𝜔₂,𝜔₃).

(a)

(b)

(c)

(d)