= Heavy-hole and light-hole bands
Near the zone centre of many cubic <semiconductors>, the upper <valence bands> have different curvatures and hence different <band effective masses>. In the isotropic approximation, the $j=3/2$ states with angular-momentum projection magnitude $3/2$ along the propagation direction form the heavy-hole branch; projection magnitude $1/2$ gives the light-hole branch. A flatter downward electron dispersion corresponds to a larger positive <electron hole> effective mass. Crystal anisotropy, strain and confinement can mix these branches, so the labels do not imply direction-independent exact masses.
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