In ZnO-based two-dimensional electron systems with strong Coulomb interaction, the anomalous spin-exciton branch is revealed. As probed by inelastic light scattering, in a ferromagnetic quantum-Hall state with the filling factor $\nu =2$, a spin exciton has a negative momentum dispersion with steepness dependent on the electron density. The negative dispersion of the spin exciton is associated with its interaction with higher-energy spin-flip modes that exist near $\nu =2$. Surprisingly, the anti-Stokes light scattering on spin excitons at ferromagnetic state $\nu =2$ is amplified by orders of magnitude, indicating the macroscopic accumulation of these excitations. The experimental findings are confirmed by the exact diagonalization method—these calculations show a magnetoroton minimum in the dispersion of spin excitons and also the attractive interaction between magnetoroton spin excitations.

中文翻译：

---

填充因子ν = 2 的量子霍尔铁磁体中具有磁旋子最小值的反常自旋激子

在具有强库仑相互作用的 ZnO 基二维电子系统中，揭示了反常的自旋激子分支。通过非弹性光散射探测，在具有填充因子的铁磁量子霍尔态$\nu =2$，自旋激子具有负动量色散，其陡度取决于电子密度。自旋激子的负色散与其附近存在的高能自旋翻转模式的相互作用有关。$\nu =2$. 令人惊讶的是，反斯托克斯光散射在铁磁态的自旋激子上$\nu =2$被放大了几个数量级，表明这些激发的宏观积累。实验结果通过精确对角化方法得到证实——这些计算显示了自旋激子色散中的磁旋子最小值，以及磁旋子自旋激发之间的吸引力相互作用。