Magnetoluminescence of spatially indirect dipolar excitons collected in 25 nm GaAs/AlGaAs single quantum well within a lateral potential trap has been studied in perpendicular magnetic field in Faraday geometry. The paramagnetic spin splitting of the luminescence line of the heavy-hole excitons in the trap centre is completely compensated at magnetic fields below critical value, around 2 Tesla. The effect of spin-splitting compensation is caused by the exchange interaction in dense exciton Bose gas which is in qualitative agreement with the existing theoretical concepts. In the range of low magnetic fields, less than 1.5 Tesla, an unusually large blue shift, upto 3 meV, is observed, which is related to in-plane electric field component present in nonhomogeneous electrostatic field of the trap.

9 pages, 3 figures