= Spin normalization in two-dimensional free-electron state counting
{title2=$g(\epsilon)=g_sAm/(2\pi\hbar^2)$}
Each allowed <wavevector> occupies <area> $(2\pi)^2/A$ under <periodic boundary conditions>, for each independent <spin> state. For <parabolic dispersion>, the number below <energy> $\epsilon$ is $g_sAm\epsilon/(2\pi\hbar^2)$. Thus the often-quoted coefficient $Am/(2\pi\hbar^2)$ is per <spin>. Unpolarized <electrons> have $g_s=2$; the same convention must be used in particle counting and the <Fermi energy>. A linear Dirac <dispersion> has a different <energy> dependence.
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