Theory of a condensed charged-bose,charged-fermi gas

Field-theoretic methods are used to derive the low-temperature properties of a dense, neutral gas of condensed charged (+Ze) bosons (mass M) and degenerate charged (?e) fermions (mass m). The density-density correlation function exhibits two collective modes for m ? M: a plasmon branch and a phonon branch with speed $\text{c = V}{}_{\mathrm{F}}\text{(}\text{Zm}\text{3M}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. Boson single-particle excitations are gapless and coincide with the phonon mode at low k. Inclusion of the two interacting dynamical components leads to small shifts in the boson and fermion ground-state energy and boson depletion relative to the values obtained for models with rigid, inert, neutralizing backgrounds.