Observation of Quantum Hall Valley Skyrmions
  We report measurements of the interaction-induced quantum Hall effect in a spin-polarized AlAs two-dimensional electron system where the electrons occupy two in-plane conduction band valleys. Via the application of in-plane strain, we tune the energies of these valleys and measure the energy gap of the quantum Hall state at filling factor $\nu$ = 1. The gap has a finite value even at zero strain and, with strain, rises much faster than expected from a single-particle picture, suggesting that the lowest energy charged excitations at $\nu=1$ are "valley Skyrmions". 
Y. P. Shkolnikov, S. Misra, N. C. Bishop, E. P. De Poortere, and M.   Shayegan