The Interaction in the Macroscopically Ordered Exciton State
  The macroscopically ordered exciton state (MOES) - a periodic array of beads with spatial order on a macroscopic length - appears in the external exciton rings at low temperatures below a few Kelvin. Here, we report on the experimental study of the interaction in the MOES. The exciton PL energy varies in concert with the intensity along the circumference of the ring, with the largest energy found in the brightest regions. This shows that the MOES is characterized by the repulsive interaction and is not driven by the attractive interaction. 
Sen Yang, A.V. Mintsev, A.T. Hammack, L.V. Butov, A.C. Gossard