Optically Pumped NMR Evidence for Finite-Size Skyrmions in GaAs Quantum Wells near Landau Level Fillingν=1

The Knight shift $\left[K_s\right(\nu ,T\left)\right]$ and spin-lattice relaxation time $\left[T_1\right(\nu ,T\left)\right]$ of the ${}^{71}\mathrm{Ga}$ nuclei located in $n$-doped GaAs quantum wells are measured using optically pumped NMR, for Landau level filling $0.66<\mathrm{}\nu <1.76\mathrm{}$ and temperature $1.55<T<\mathrm{}20\mathrm{}$ K. $K_s\left(\nu \right)$ [proportional to the electron spin polarization $〈S_z\left(\nu \right)〉$] drops precipitously on either side of $\nu =1\mathrm{}$, which is evidence that the charged excitations of the $\nu =1\mathrm{}$ ground state are finite-size Skyrmions. For $\nu <1\mathrm{}$, the data are consistent with a many-body ground state which is not fully spin polarized, with a very small spin excitation gap that increases as $\nu \to \frac{2}{3}$.