THE MASS-ACTION LAW IN 2-COMPONENT FERMI SYSTEMS REVISITED - EXCITONS AND ELECTRON-HOLE PAIRS

Taking up the quantum-statistical derivation of a mass action law for two-component Fermi systems with Coulomb interaction given previously an improved density formula for either species is presented. It expresses the densities as a sum of a free quasi-particle part and a correlated contribution resulting from bound and scattering states. Avoiding the resolvent-technique for the solution of the T-matrix equation the correlated density is directly expressed in terms of on-shell quantities, eventually the scattering phase shifts. The ionization equilibrium of excitons, electrons, and holes is quantitatively analyzed by model calculations for a cut-off Coulomb potential. The possibility of Bose-Einstein condensation of scattering states is inspected.