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

Recently, the observed mode splitting in doped Sm1-x Yx S was explained by the local symmetry breaking produced by the Y impurities. A model with a random quantization axis mi 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 mi, thereby enhancing the Van Vleck susceptibility with increasing x. Due to the level splitting in a magnetic field, the mode frequencies of Sm1-x Yx S will be broadened asymmetrically: at the (111) zone center (boundary), the lower mode will be significantly broadened (narrowed) compared to the upper mode.