Spin parity effects in monoaxial chiral ferromagnetic chain*

We describe a fully quantum mechanical treatment of solitons in monoaxial chiral ferromagnets in 1d, which contrasts with the majority of theoretical studies to date  on chiral magnetic solitons (in 1d)/skyrmions (2d) that rely on a classical or at best semiclassical framework.  We begin with a reasonably generic model for this class of magnets, where we find numerically that  the magnetization curve behaves differently depending on  whether the spin quantum number is half-odd integer or integer: a clear indication that quantum effects are at play.  As a leverage for unraveling how this comes about, we then construct a model where the number of solitons of heights 1 through 2S are all seperately  conserved quantities. This leads us to an exact formula relating the set of soliton numbers to the crystal momentum of the ground state, which in turn reproduces the observed behavior. Finally, we establish numerically that the constructed Hamiltonian is a good description of the generic model we started out with. We think the present approach, which replaces the semiclassical "winding-spin picture" of solitons with spin configurations involving quantized steps,  can help gain a better understanding of the quantum nature of solitons, skyrmions and domain walls, in chiral and non-chiral magnets alike. This contribution is based on preprint arXiv:2209.04227, authored by Sohei Kodama,  Yusuke Kato, and the presenter.