  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.
