Spectroscopic Evidence for the Localization of Skyrmions near Nu=1 as   T->0
  Optically pumped nuclear magnetic resonance measurements of Ga-71 spectra were carried out in an n-doped GaAs/Al0.1Ga0.9As multiple quantum well sample near the integer quantum Hall ground state Nu=1. As the temperature is lowered (down to T~0.3 K), a ``tilted plateau'' emerges in the Knight shift data, which is a novel experimental signature of quasiparticle localization. The dependence of the spectra on both T and Nu suggests that the localization is a collective process. The frozen limit spectra appear to rule out a 2D lattice of conventional skyrmions. 
P. Khandelwal, A. E. Dementyev, N. N. Kuzma, S. E. Barrett (Yale   University), L. N. Pfeiffer, and K. W. West (Bell Labs)