Simon Brecht G, Kurdi Samer, La Helena, Bertelli Iacopo, Carmiggelt Joris J, Ruf Maximilian, de Jong Nick, van den Berg Hans, Katan Allard J, van der Sar Toeno
Department of Quantum Nanoscience, Kavli Institute of Nanoscience, Delft University of Technology, 2628 CJ Delft, The Netherlands.
Huygens-Kamerlingh Onnes Laboratorium, Leiden University, 2300 RA Leiden, The Netherlands.
Nano Lett. 2021 Oct 13;21(19):8213-8219. doi: 10.1021/acs.nanolett.1c02654. Epub 2021 Oct 1.
Controlling magnon densities in magnetic materials enables driving spin transport in magnonic devices. We demonstrate the creation of large, out-of-equilibrium magnon densities in a thin-film magnetic insulator via microwave excitation of coherent spin waves and subsequent multimagnon scattering. We image both the coherent spin waves and the resulting incoherent magnon gas using scanning-probe magnetometry based on electron spins in diamond. We find that the gas extends unidirectionally over hundreds of micrometers from the excitation stripline. Surprisingly, the gas density far exceeds that expected for a boson system following a Bose-Einstein distribution with a maximum value of the chemical potential. We characterize the momentum distribution of the gas by measuring the nanoscale spatial decay of the magnetic stray fields. Our results show that driving coherent spin waves leads to a strong out-of-equilibrium occupation of the spin-wave band, opening new possibilities for controlling spin transport and magnetic dynamics in target directions.
控制磁性材料中的磁振子密度能够驱动磁振子器件中的自旋输运。我们通过对相干自旋波进行微波激发并随后进行多磁振子散射，展示了在薄膜磁性绝缘体中产生大的非平衡磁振子密度。我们使用基于金刚石中电子自旋的扫描探针磁力测量法对相干自旋波和由此产生的非相干磁振子气体进行成像。我们发现该气体从激发带状线单向延伸数百微米。令人惊讶的是，气体密度远远超过遵循具有化学势最大值的玻色 - 爱因斯坦分布的玻色子系统所预期的密度。我们通过测量磁杂散场的纳米级空间衰减来表征气体的动量分布。我们的结果表明，驱动相干自旋波会导致自旋波带的强烈非平衡占据，为在目标方向上控制自旋输运和磁动力学开辟了新的可能性。
