T-shaped quantum wires in magnetic fields: Weakly confined magnetoexcitons beyond the diamagnetic limit

Optical excitations of magnetoexcitons in T-shaped wires are calculated and compared with experiment. We find the single-particle states for electrons and holes confined to a wire in a magnetic field and use these states as a basis for calculations of magnetoexciton states. We accurately reproduce the field dependence of the exciton states and explain the small, field-induced, energy shifts that are observed for these states. The shifts are small because the T-junction provides weak confinement, rather than strong quantum confinement. Diamagnetic shifts calculated from perturbation theory fail to describe the experimental results. We determine when perturbation theory is valid for these nanostructures and which gauge should be used to give the diamagnetic shift that best reproduces the field dependence at low fields.