Drude Formulas
σ(ω) = σ₀/(1-iωτ)
σ₀ = ne²τ/m
Re[σ] = σ₀/(1+(ωτ)²)
Im[σ] = σ₀·ωτ/(1+(ωτ)²)
Electrons accelerate in E-field and scatter with rate 1/τ. The Drude model predicts DC conductivity σ₀ = ne²τ/m and Lorentzian frequency response — the basis for optical conductivity in metals.