= Heat capacity for a two-dimensional linear fermion dispersion
{title2=$C_+=9g\zeta(3)Ak_B^3T^2/(4\pi\hbar^2v^2)$}
For $g$ copies of a positive-energy branch $E=\hbar v|\mathbf k|$ in <area> $A$, the <density of states> is $D(E)=gAE/(2\pi\hbar^2v^2)$. At zero <chemical potential>, the thermal <energy> is $3g\zeta(3)A(k_BT)^3/(4\pi\hbar^2v^2)$, giving the displayed fixed-zero-chemical-potential <heat capacity>. If a symmetric filled negative-energy band also supplies holes, its excitation <energy> contributes an equal amount. Counting cones, <spin> species and holes explicitly is necessary before assigning an absolute numerical coefficient.
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