Magneto-optical study of excitonic states inIn0.045Ga0.955As/GaAsmultiple coupled quantum wells

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The excitonic states have been investigated in ${\mathrm{In}}_{0.045}{\mathrm{Ga}}_{0.955}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures consisting of i quantum wells $(i=1,2,3,4)$ with 7.5 nm well thickness. For a 2.5 nm barrier thickness between the wells, the electronic states are strongly coupled. Because of the coupling, the heavy-hole exciton $\mathrm{ns}\mathrm{hh}$ of each single quantum well is split into ${i}^{2}$ states. The states can be characterized according to their symmetry under a combination of the reflections of the single particles at the quantum-well plane. The energy order of the symmetric and antisymmetric states as a function of quantum-well number is investigated in detail, and compares well to the theoretical calculation. These coupled quantum-well structures exhibit somewhat three-dimensional character based on the study of their exciton binding energies and wave functions. Highly resolved photoluminescence excitation spectra are presented, measured in magnetic fields up to 13 T using circularly polarized light. Strong mixing between light- and heavy-hole excitons causes optical transitions into high-angular-momentum exciton states and strong anticrossing effects. An anticrossing between the $3d{\mathrm{hh}}_{11}$ and ${\mathrm{hh}}_{21}$ exciton is observed. Also, the light-hole exciton is found to possess ${\ensuremath{\Gamma}}_{7g}$ and ${\ensuremath{\Gamma}}_{6g}$ symmetries.