= Carrier density from spin-degenerate quantum oscillations
One resolved spin branch of a two-dimensional <Landau level> has degeneracy $eB/h$ per area. Thus the total <carrier density> is $n_s=\nu eB/h$, where the <filling factor> $\nu$ counts all occupied spin and other internal branches, including partial filling. If consecutive unsplit orbital peaks change filling by an unresolved degeneracy $g_d$,
$$
n_s=\frac{g_d e}{h\Delta(1/B)}.
$$
For only spin degeneracy, $g_d=2$. Once spin splitting is resolved, adjacent individual branches differ by one rather than two; counting split subpeaks as unsplit orbital peaks gives a factor-two error.
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