Investigation of localization in using hyperfine interaction

At magnetic fields where an oscillatory structure in the Hall constant R-H = rho(xy)/B points to the localization of electrons, we investigate the NMR -induced change in the transverse magnetoresistivities. Because the nuclear hyperfine field B-HF acts only on the spin of the Electrons, the role of s pin-splitting can be seperated from that of the external magnetic field for the magnetic field dependence of R-H. This experiment shows that the oscil latory structure in R-H is directly related to a redistribution in the occu pation of the two spin states in the lowest Landau level.