the long-range current-current interactions between CF’s produce inelastic scattering at a rate comparable to the energy of the CF quasiparticles relative to the Fermi energy. However, for the low-temperature DC thermopower responses, which are the focus of this paper, such inelastic scattering processes are less important than ordinary elastic scattering from impurities and can be neglected.

Let us define: $$\sigma_0 = \frac{k_F\ell}{4\pi};\,\,\,  \alpha_0= \frac{{\L} T}{v_F} \frac{{\partial}\sigma_0}{{\partial}k_F}
\label{definition}$$ where $\L = \frac{\pi^2k_B^2}{3e^2}$ is the Lorenz number, and $v_F,k_F$ are the composite Fermi velocity and wave-vector respectively, in units where $e,\hbar=1$. In this regime, $\hat\sigma_\text{D} \approx \sigma_0 \hat{1}$ is the DC conductivity of the composite Fermi surface with Fermi-wave-vector $k_F$ and transport mean-free path $\ell$, and similarly $\hat\alpha_\text{D}\approx \alpha_0\hat 1$ is the composite Fermi-surface thermoelectric conductivity. The transverse (Hall) components $\sigma^{xy}_\text{D},\alpha^{xy}_\text{D}$ vanish by PHS (which acts as an effective time-reversal symmetry on the CFs [@Son15; @Wang15short; @Metlitski15]). While impurities locally break PHS, and only preserve PHS on average, for the long-wavelength impurity potentials relevant to GaAs, we can show that such extrinsic sources of $\sigma^{xy}_D$ are negligibly small (see Appendix \[app:Disorder\]). Lastly, we note that the response coefficients $\sigma_D,\alpha_D$ should be interpreted as transport coefficients (i.e. obtained from Kubo formulae by appropriately 