We present the first reliable calculation of the collective mode structure of
a strongly coupled electronic bilayer. The calculation is based on a classical
model through the 3rd frequency-moment-sum-rule preserving Quasi Localized
Charge Approximation, using the recently calculated Hypernetted Chain pair
correlation functions. The spectrum shows an energy gap at k=0 and the
absence of a previously conjectured dynamical instability.Comment: 4 pages, 4 .ps figure