Orbital angular momentum of azimuthal spin waves

方位角スピン波の軌道角運動量

Valet, T.*; 山本 慧   ; Pigeau, B.*; de Loubens, G.*; Klein, O.*

Valet, T.*; Yamamoto, Kei; Pigeau, B.*; de Loubens, G.*; Klein, O.*

In the context of a growing interdisciplinary interest in the angular momentum of wave fields, the spin-wave case has yet to be fully explored, with the extensively studied notion of spin transport being only part of the broader picture. Here we report experimental evidence for non-zeromagnon orbital angular momentum inside magnetic disk, by resolving the frequency splitting between magnon modes with counter-rotating wavefronts and thereby avoiding formation of azimuthal standing waves. This requires an unambiguous formulation of spin and orbital angular momenta for spin waves, which we provide in full generality taking advantage of a systematic application of quantum field theory techniques as detailed in an associated article. The results unequivocally establish magnetic dipole-dipole interactions as a magnetic-field controllable spin-orbit interaction for magnons. Our findings open a new research direction, leveraging the spectroscopic readability of angular momentum for azimuthal spin waves and other related systems.