Clustering of the electron–hole liquid

Free excitons created in semi-metals and semiconductors under irradiation of light may condense into an electron–hole liquid when their density is large enough. This quantum phenomenon has been intensively studied theoretically and experimentally. The exciton gas undergoes Mottʹs metal insulator phase transition at much lower density. This mismatch between the critical value of the density for the instability of the free excitons and the threshold value of the density for the appearance of the electron–hole liquid stimulated a controversial dispute over a decade of what arises in the range of densities between these two critical values. We show that a new structural liquid consisting of the charged clusters can be formed where each cluster is like a molecule consisting of different numbers of electrons and holes.