Max-Planck-Institute of Quantum Optics, Garching, Germany.
Fakultät für Physik, Ludwig-Maximilians-Universität München, Garching, Germany.
Nature. 2019 Jul;571(7764):240-244. doi: 10.1038/s41586-019-1333-x. Epub 2019 Jun 26.
The enigmatic interplay between electronic and magnetic phenomena observed in many early experiments and outlined in Maxwell's equations propelled the development of modern electromagnetism. Today, the fully controlled evolution of the electric field of ultrashort laser pulses enables the direct and ultrafast tuning of the electronic properties of matter, which is the cornerstone of light-wave electronics. By contrast, owing to the lack of first-order interaction between light and spin, the magnetic properties of matter can only be affected indirectly and on much longer timescales, through a sequence of optical excitations and subsequent rearrangement of the spin structure. Here we introduce the regime of ultrafast coherent magnetism and show how the magnetic properties of a ferromagnetic layer stack can be manipulated directly by the electric-field oscillations of light, reducing the magnetic response time to an external stimulus by two orders of magnitude. To track the unfolding dynamics in real time, we develop an attosecond time-resolved magnetic circular dichroism detection scheme, revealing optically induced spin and orbital momentum transfer in synchrony with light-field-driven coherent charge relocation. In tandem with ab initio quantum dynamical modelling, we show how this mechanism enables the simultaneous control of electronic and magnetic properties that are essential for spintronic functionality. Our study unveils light-field coherent control of spin dynamics and macroscopic magnetic moments in the initial non-dissipative temporal regime and establishes optical frequencies as the speed limit of future coherent spintronic applications, spin transistors and data storage media.
在许多早期实验中观察到的电子和磁现象之间的神秘相互作用，以及麦克斯韦方程组中概述的相互作用，推动了现代电磁学的发展。今天，超短激光脉冲的电场的完全控制演化使得物质的电子特性能够直接且超快地进行调整，这是光波电子学的基石。相比之下，由于光和自旋之间缺乏一阶相互作用，物质的磁性只能通过一系列光激发和随后的自旋结构重新排列来间接地、在更长的时间尺度上进行影响。在这里，我们引入超快相干磁性的概念，并展示了如何通过光的电场振荡直接操纵铁磁层叠的磁性，将对外界刺激的磁响应时间缩短两个数量级。为了实时跟踪展开的动力学，我们开发了一种阿秒时间分辨的磁圆二色性检测方案，揭示了与光场驱动的相干电荷重排同步的光诱导自旋和轨道动量转移。与从头算量子动力学建模相结合，我们展示了这种机制如何能够同时控制电子和磁性，这对于自旋电子学功能至关重要。我们的研究揭示了光场在初始非耗散时间域中对自旋动力学和宏观磁矩的相干控制，并确立了光频作为未来相干自旋电子应用、自旋晶体管和数据存储介质的速度限制。
