Ogawa N, Köhler L, Garst M, Toyoda S, Seki S, Tokura Y
RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan;
Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan.
Proc Natl Acad Sci U S A. 2021 Feb 23;118(8). doi: 10.1073/pnas.2022927118.
Nonreciprocity emerges in nature and in artificial objects from various physical origins, being widely utilized in contemporary technologies as exemplified by diode elements in electronics. While most of the nonreciprocal phenomena are realized by employing interfaces where the inversion symmetry is trivially lifted, nonreciprocal transport of photons, electrons, magnons, and possibly phonons also emerge in bulk crystals with broken space inversion and time reversal symmetries. Among them, directional propagation of bulk magnons (i.e., quanta of spin wave excitation) is attracting much attention nowadays for its potentially large nonreciprocity suitable for spintronic and spin-caloritronic applications. Here, we demonstrate nonreciprocal propagation of spin waves for the conical spin helix state in CuOSeO due to a combination of dipole and Dzyaloshinskii-Moriya interactions. The observed nonreciprocal spin dispersion smoothly connects to the hitherto known magnetochiral nonreciprocity in the field-induced collinear spin state; thus, all the spin phases show diode characteristics in this chiral insulator.
非互易性在自然界和各种物理起源的人造物体中出现，在当代技术中被广泛应用，例如电子学中的二极管元件。虽然大多数非互易现象是通过采用打破空间反演对称性的界面来实现的，但光子、电子、磁振子以及可能的声子的非互易输运也会出现在具有空间反演和时间反演对称性破缺的体晶体中。其中，体磁振子（即自旋波激发的量子）的定向传播因其适用于自旋电子学和自旋热电子学应用的潜在大非互易性而备受关注。在此，我们证明了由于偶极相互作用和Dzyaloshinskii-Moriya相互作用的结合，CuOSeO中锥形自旋螺旋态的自旋波具有非互易传播特性。观察到的非互易自旋色散与迄今已知的场诱导共线自旋态中的磁手性非互易性平滑连接；因此，在这种手性绝缘体中，所有自旋相都表现出二极管特性。
