  We study the multistable behavior of the intersubband optical absorption for
InSb-based tunnel coupled quantum wells. We consider four sublevels coming from
the Zeeman spin splitting of the two deepest levels, caused by a weak in-plane
magnetic field. Photoexcitation with an intense terahertz pump produces the
redistribution of nonequilibrium electrons between the spin sublevels. Based on
the matrix density, we describe this electron redistribution by means of a
system of balance equations for electron concentrations. The redistribution
produces a photoinduced self-consistent potential, giving rise to the
renormalization of energy distance between levels. Depending on total electron
concentration and pumping efficiency, we find different multistable behaviors
in the intersubband optical absorption spectrum.
