Broken local symmetry and the mode splitting of Y doped SmS in a magnetic field

摘要

Recently, the observed mode splitting in doped Sm_(1-x)Y_xS was explained by the local symmetry breaking produced by the Y impurities. A model with a random quantization axis m_i successfully fit not only the observed mode frequencies of the J=0→1 transitions but also their intensities, which depend strongly on wave vector. A magnetic field is now predicted to significantly alter the magnetic susceptibility and mode frequencies by mixing the J=0 and J=1 levels. The induced Sm moments form a canted structure, with each Sm spin rotated from the field direction towards the local quantization axis m_i, thereby enhancing the Van Vleck susceptibility with increasing x. Due to the level splitting in a magnetic field, the mode frequencies of Sm_(1-x)Y_xS will be broadened asymmetrically: at the (111) zone center (boundary), the lower mode will be significantly broadened (narrowed) compared to the upper mode.