Institute for Applied Physics and Center for Nonlinear Science, University of Muenster, Corrensstrasse 2-4, 48149, Muenster, Germany.
Department of Physics, Emory University, Atlanta, GA, 30322, USA.
Nat Commun. 2017 Nov 17;8(1):1579. doi: 10.1038/s41467-017-01937-y.
Pure spin currents provide the possibility to control the magnetization state of conducting and insulating magnetic materials. They allow one to increase or reduce the density of magnons, and achieve coherent dynamic states of magnetization reminiscent of the Bose-Einstein condensation. However, until now there was no direct evidence that the state of the magnon gas subjected to spin current can be treated thermodynamically. Here, we show experimentally that the spin current generated by the spin-Hall effect drives the magnon gas into a quasi-equilibrium state that can be described by the Bose-Einstein statistics. The magnon population function is characterized either by an increased effective chemical potential or by a reduced effective temperature, depending on the spin current polarization. In the former case, the chemical potential can closely approach, at large driving currents, the lowest-energy magnon state, indicating the possibility of spin current-driven Bose-Einstein condensation.
纯自旋电流为控制导磁和绝缘磁性材料的磁化状态提供了可能。它可以增加或减少磁振子的密度，并实现类似于玻色-爱因斯坦凝聚的磁化强度相干动力学状态。然而，直到现在还没有直接的证据表明，经受自旋电流的磁振子气体的状态可以用热力学来处理。在这里，我们通过实验证明，由自旋霍尔效应产生的自旋电流将磁振子气体驱动到准平衡状态，该状态可以用玻色-爱因斯坦统计来描述。磁振子的种群函数的特征是有效化学势的增加或有效温度的降低，这取决于自旋电流的极化。在前一种情况下，在大的驱动电流下，化学势可以非常接近最低能量磁振子状态，这表明自旋电流驱动的玻色-爱因斯坦凝聚是可能的。
