  On a high-mobility 2D electron gas we have observed, in strong magnetic
fields (omega_{c} tau > 1), a parabolic negative magnetoresistance caused by
electron-electron interactions in the regime of k_{B} T tau / hbar ~ 1, which
is the transition from the diffusive to the ballistic regime. From the
temperature dependence of this magnetoresistance the interaction correction to
the conductivity delta sigma_{xx}^{ee}(T) is obtained in the situation of a
long-range fluctuation potential and strong magnetic field. The results are
compared with predictions of the new theory of interaction-induced
magnetoresistance.
