Instability toward biexciton crystallization in one-dimensional   electron-hole systems
  One-dimensional (1D) electron-hole (e-h) systems in a high-density regime is investigated by means of bozonization techniques. It turned out that the systems are insulating even at the high density limit and that the exciton Mott transition (insulator-to-metal transition) never occurs at absolute zero temperature. The insulating ground state exhibits a strong instability towards the crystallization of biexcitons. 
Kenichi Asano, Tetsuo Ogawa