  The evolution of the fractional quantum Hall state at filling 5/2 is studied
in density tunable two-dimensional electron systems formed in wide wells in
which it is possible to induce a transition from single to two subband
occupancy. In 80 and 60 nm wells, the quantum Hall state at 5/2 filling of the
lowest subband is observed even when the second subband is occupied. In a 50 nm
well the 5/2 state vanishes upon second subband population. We attribute this
distinct behavior to the width dependence of the capacitive energy for
intersubband charge transfer and of the overlap of the subband probability
densities.
