Excitation Energy Dependence of the Exciton Inner Ring
  We report on the excitation energy dependence of the inner ring in the exciton emission pattern. The contrast of the inner ring is found to decrease with lowering excitation energy. Excitation by light tuned to the direct exciton resonance is found to effectively suppress excitation-induced heating of indirect excitons and facilitate the realization of a cold and dense exciton gas. The excitation energy dependence of the inner ring is explained in terms of exciton transport and cooling. 
Y. Y. Kuznetsova, J. R. Leonard, L. V. Butov, J. Wilkes, E. A.   Muljarov, K. L. Campman, A. C. Gossard
cond-mat.mes-hall