Magnetic-field-induced substructures in multiple quantum wells consisting of magnetic and nonmagnetic semiconductor layers

We have investigated multiple quantum well systems consisting of diluted magnetic $\left({\mathrm{Zn}}_{1-x-y}{\mathrm{Cd}}_x{\mathrm{Mn}}_y\mathrm{Se}\right)$ and nonmagnetic $\left({\mathrm{Zn}}_{1-x}{\mathrm{Cd}}_x\mathrm{Se}\right)$ semiconductor wells, separated by nonmagnetic ZnSe barriers. By focusing on interband transitions involving the lowest multiplet of states (i.e., the ground state split by interwell interactions), we were able to study the details of the coupling between the wells. The strongest interaction between the states of each well occurs when the wells are identical (i.e., when they are in a resonant condition). The coupling between the wells is dramatically reduced in the presence of an external magnetic field, which can change the depth of diluted magnetic semiconductor (DMS) wells relative to the non-DMS wells via the large Zeeman splitting that occurs in the DMS layers. As soon as the depth of the wells becomes unequal, the multiple quantum well system subdivides into separate subsystems consisting of groups of equal (resonant) wells, one associated with non-DMS wells, and the other with DMS wells. This is clearly evident both from theoretical investigation and from the observed magnetic-field dependence of the absorption lines associated with the ground-state multiplet.