Acoustic plasma modes

For a two-component Fermion system the coupled Boltzmann equations are solved for the eigenvalues of the collective modes. Exchange and correlation are taken into account. We find three acoustic plasma modes, one of which is strongly Landau damped by both the light mass (m1) and the heavy mass (m2) particles. The two other modes are damped only the the m1 system; their ''sound'' velocities depend on two parameters: m2/m1 and r/sub s/ (the usual electron spacing parameter for system 1). In the high-density limit, r/sub s/ = 0, these two modes exist whenever m2/m1>2.25. One of the two modes is the well-known Froehlich mode, and the other is a low-Q mode. Its sound velocity is approx.0.8v/sub F/1 (Fermi velocity of system 1). The effect of exchange and correlation are to substantially reduce the frequency of the Froehlich mode; the low-Q mode is practically unaffected. The Landau damping of the two modes depends strongly on m2/m1 and r/sub s/