  The subbands of weakly coupled double-layer two dimensional electron gas
systems consist of narrowly spaced pairs whose corresponding wavefunctions are
symmetric and antisymmetric combinations of isolated layer subband
wavefunctions. The energetic spacing within a pair is 2t where t is the
interlayer tunneling amplitude. t is an important parameter in modeling these
systems and, if interactions could be neglected, it would be proportional to
beating frequencies seen in weak-field magnetic oscillations experiments and
therefore readily measurable. We point out that interactions alter the beating
frequency. We discuss similarities and differences between this effect and
exchange-correlation enhanced spin-splitting.
