Figure 2.

The Lorentz number $\mathcal{L}={\kappa }_{\mathrm{el}}/\left(\sigma T\right)$ for massless Dirac fermions as a function of the chemical potential. Solid lines represent the approximations given by Equation (36) (blue line) and Equation (39) (red line). Dashed lines (top to bottom) depict the two corresponding $\mu =0$ values, and the value of ${\mathcal{L}}_0=({\pi }^2/3)k_B^2/e^2$ representing the Wiedemann–Franz law restored in the $\left|\mu \right|\gg k_{B}T$ limit.