Collective excitations and quantum incompressibility in electron-hole bilayers

We apply quantum continuum mechanics to the calculation of excitation spectrum a coupled electron-hole bilayer. The theory expresses energies in terms ground-state intra- and interlayer pair correlation functions, which are available from Monte Carlo calculations. final formulas for collective modes deduced this approach coincide with obtained ``quasilocalized particle approximation'' by Kalman et al. [G. Kalman, V. Valtchinov, K. I. Golden, Phys. Rev. Lett. 82, 3124 (1999)], likewise predicts existence gapped excitations charged channel, gap arising correlation. An immediate consequence is that static density-density response function channel vanishes as ${q}^{2}$ wave vector $q\ensuremath{\rightarrow}0$, rather than linearly $q$, commonly expected. In sense, system incompressible. This feature, has no analog classical plasma, consistent an excitonic ground state implies discontinuity chemical potential electrons holes when numbers equal. It should be experimentally observable monitoring densities potentials attempt change these opposite directions.