Fig. 3

The σ ⁰⁰ and σ ¹¹ conductivities per band. σ ⁰⁰ falls as 1/T (although with different proportionality constants) in both temperature ranges ω ₀ ≪ T ≪ μ/λ and μ/λ ≪ T ≪ μ. σ ¹¹ grows in the lower range of T, then saturates as it approaches the value e ²/2π in the higher. This is calculated for a two-dimensional tight binding model, in which the phonon displacement couples to the nearest-neighbor hopping amplitude of the electrons