  The only kinematically-allowed phonon-scattering events for bands of subsonic
fermions ($v_F < v_p$) are interband transitions, leading to different low-$T$
transport physics than in the typical supersonic case. We apply a kinetic
theory of phonon-limited transport to a generic two-band system of subsonic
fermions, deriving formulae for relaxation times and resistivity that are
accurate in the limit of close bands and small $v_F/v_p$. We predict regimes of
$\rho \propto T$, $\rho \propto T^2$, and perfect conductivity. Our theory
predicts linear-in-$T$ resistivity down to a crossover temperature that is
suppressed from its supersonic analogue by a factor of $v_F/v_p$, offering a
new explanation for low-$T$ "strange metal" behavior observed in flat band
systems.

Mesoscale and Nanoscale Physics;Materials Science