Measurements of composite fermion masses from the spin polarization of two-dimensional electrons in the region 1<ν<2 -: art. no. 161305

Measurements of the reflectivity of a two-dimensional electron gas are used to deduce the polarization of the composite fermion of hole system formed for Landau level occupancies in the regime 1<nu<2. The measurements are consistent with the formation of a mixed spin CF system and allow the density of states or 'polarization' effective mass of the CF holes to be determined. The mass values at nu=3/2 are found to be similar to1.9m(e) for electron densities of 4.4x10(11) cm(-2), which is significantly larger than those found from measurements of the energy gaps at finite values of effective magnetic field.