Measurements on a multilayer two-dimensional electron system (2DES) near Landau-level filling $\nu =1\mathrm{}$ reveal the disappearance of the nuclear spin contribution to the heat capacity as the ratio $\tilde{g}$ between the Zeeman and Coulomb energies exceeds a critical value ${\tilde{g}}_c\approx 0.04$. This disappearance suggests the vanishing of the Skyrmion-mediated coupling between the lattice and the nuclear spins as the spin excitations of the 2DES make a transition from Skyrmions to single spin flips above ${\tilde{g}}_c$. Our experimental ${\tilde{g}}_c$ is smaller than the calculated ${\tilde{g}}_c=0.054\mathrm{}$ for an ideal 2DES. We discuss possible origins of this discrepancy.

• Received 10 March 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.2764