Polarized fine structure in the excitation spectrum of a negatively   charged quantum dot
  We report polarized photoluminescence excitation spectroscopy of the negative trion in single charge tunable InAs/GaAs quantum dots. The spectrum exhibits a p-shell resonance with polarized fine structure arising from the direct excitation of the electron spin triplet states. The energy splitting arises from the axially symmetric electron-hole exchange interaction. The magnitude and sign of the polarization are understood from the spin character of the triplet states and a small amount of quantum dot asymmetry, which mixes the wavefunctions through asymmetric e-e and e-h exchange interactions. 
M. E. Ware, E. A. Stinaff, D. Gammon, M. F. Doty, A. S. Bracker, D.   Gershoni, V. L. Korenev, S. C. Badescu, Y. Lyanda-Gell...