Searches for skyrmions in the limit of zero g-factor

Energy gaps have been measured for the ferromagnetic quantum Hall effect states at ν = 1 and 3 in GaAs/Ga0.7Al0.3As heterojunctions as a function of Zeeman energy, which is reduced to zero by applying hydrostatic pressures of up to 20 kbar. At large Zeeman energy the gaps are consistent with spin-wave excitations. For a low-density sample the gap at ν = 1 decreases with increasing pressure and reaches a minimum when the g-factor vanishes. At small Zeeman energy the excitation appears to consist of a large number of reversed spins and may be interpreted as a skyrmion. The data also suggest that skyrmionic excitations take place at ν = 3. The width of the minimum at ν = 1 is found to decrease as the g-factor is reduced in a similar way for all samples.