Spin stiffness of a Fermi liquid in the ν=1 quantum Hall regime

Anomalous behavior of spin stiffness is revealed in ZnO-based two-dimensional electron systems (2DESs) with strong Coulomb interaction and Wigner-Seitz parameter ${r}_s>6$. The spin stiffness is extracted directly from the quadratic $k$ dispersion of spin excitons at $\ensuremath{\nu}=1$ probed by inelastic light scattering. The resulting values are found to be dramatically rescaled compared to the case of weakly interacting 2DESs---spin stiffness turned out to be of the order of the cyclotron energy with the effective mass of Fermi-liquid quasiparticles. This result is also confirmed by the exact diagonalization simulations.