Fermi-edge heat-capacity counting
= Fermi-edge heat-capacity counting
{c}
Only single-particle states within order $k_BT$ of the <Fermi energy> can change occupation at low <temperature>. Their number is order $g(E_F)k_BT$, and their excitation <energy> is order $k_BT$, giving $U-U_0\propto T^2$ and electronic <heat capacity> proportional to $T$.