  A technique is proposed for creating nonground-state Bose-Einstein
condensates in a trapping potential by means of the temporal modulation of
atomic interactions. Applying a time-dependent spatially homogeneous magnetic
field modifies the atomic scattering length. An alternating modulation of the
scattering length excites the condensate, which, under special conditions, can
be transferred to an excited nonlinear coherent mode. It is shown that there
occurs a phase-transition-like behavior in the time-averaged population
imbalance between the ground and excited states. The application of the
suggested technique to realistic experimental conditions is analyzed and it is
shown that the considered effect can be realized for experimentally available
condensates.
