Pulsed-magnetic-field measurements of the composite-fermion effective mass

Magnetotransport measurements of composite fermions (CF's) are reported in 50-T pulsed magnetic fields. The CF effective mass is found to increase approximately linearly with the effective field B*, in agreement with our earlier work at lower fields. For a B* of 14 T it reaches 1.6m(e), over 20 times the band-edge electron mass. Data from all fractions are unified by the single parameter B* for all the samples studied over a wide range of electron densities. The energy gap is found to increase like root B* at high fields.