Institute for Theoretical Physics, Utrecht University, Princetonplein 5, 3584 CC Utrecht, Netherlands.
Department of Physics, Lancaster University, Lancaster LA1 4YB, United Kingdom.
Phys Rev Lett. 2019 Sep 13;123(11):117203. doi: 10.1103/PhysRevLett.123.117203.
Magnons in ferromagnets behave as a viscous fluid over a length scale, the momentum-relaxation length, below which momentum-conserving scattering processes dominate. We show theoretically that in this hydrodynamic regime viscous effects lead to a sign change in the magnon chemical potential, which can be detected as a sign change in the nonlocal resistance measured in spin transport experiments. This sign change is observable when the injector-detector distance becomes comparable to the momentum-relaxation length. Taking into account momentum- and spin-relaxation processes, we consider the quasiconservation laws for momentum and spin in a magnon fluid. The resulting equations are solved for nonlocal spin transport devices in which spin is injected and detected via metallic leads. Because of the finite viscosity we also find a backflow of magnons close to the injector lead. Our work shows that nonlocal magnon spin transport devices are an attractive platform to develop and study magnon-fluid dynamics.
在动量弛豫长度以下的长度尺度上，铁磁体中的磁振子表现为粘性流体，在该长度尺度以下，动量守恒散射过程占主导地位。我们从理论上表明，在这种流体动力学状态下，粘性效应导致磁振子化学势发生符号变化，这可以通过在自旋输运实验中测量的非局域电阻的符号变化来检测到。当注入器-探测器距离变得与动量弛豫长度相当时，就可以观察到这种符号变化。考虑到动量和自旋弛豫过程，我们考虑了磁振子流体中动量和自旋的准守恒定律。对于通过金属引线注入和检测自旋的非局域自旋输运器件，我们求解了这些方程。由于有限的粘性，我们还在靠近注入器引线的地方发现了磁振子的回流。我们的工作表明，非局域磁振子自旋输运器件是开发和研究磁振子流体动力学的一个有吸引力的平台。
