Spin multistability of the intersubband optical absorption in asymmetric coupled quantum wells

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.