マグノンの軌道角運動量と熱ホール効果(修士論文(2010年度))

Abstract

We theoretically investigate dynamics of the magnon wavepacket, by constructing the semiclassical equation of motion of the magnon wavepacket in insulating ferromagnets and utilizing an analogy of the electron systems. The magnon wavepacket undergoes two types of orbital motions: a self-rotation motion and a motion along the edge of the system, in other words, an edge current of magnon. These motions are attributed to the Berry curvature in momentum space, i.e., these arise from the magnon band structure. In particular, the edge current of magnon is expected to be visible by space- and time- resolved optical experimental method. Moreover, this edge current of magnon brings about the thermal Hall effect of magnon, and we present its intuitive picture. We also consider the thermal Hall effect by the linear response theory, and find correction terms to the previously known result, which are expressed as the orbital angular momentum of magnon. Furthermore, we also show that our theory is applicable to not only the exchange spin wave but also the magnetostatic spin wave. The magnetostatic spin wave has a long wave length and a good coherence in some magnet, e.g., yttrium iron garnet which is a well known material in experiments, and thus it is useful for spintronics devices.