Temporal and spectral fingerprints of ultrafast all-coherent spin switching
Temporal and spectral fingerprints of ultrafast all-coherent spin switching
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DOI：
10.1038/s41586-019-1174-7
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发表时间：
2019-05-16
期刊：
影响因子：
64.8
通讯作者：
Huber, R.
中科院分区：
文献类型：
--
作者：
Schlauderer, S.;Lange, C.;Huber, R.
未来的信息技术要求更快、低损耗的量子控制。强烈的光场促进了这条道路上的里程碑，包括诱导新的物质状态(1-3)，电子的弹道加速(4-7)和谷假自旋的相干翻转(8)。这些动力学会留下独特的“指纹”，如特征带隙或高次谐波辐射。在被势垒隔开的两个态之间切换技术上最重要的量子属性-自旋-最快、耗散最少的方法是触发全相干进动。皮秒电场和磁场的实验和理论研究表明了这种可能性(9-11)，但观察实际的自旋动力学仍然遥不可及。在这里，我们展示了太赫兹电磁脉冲允许自旋在势垒上的相干引导，并报告了相应的时间和光谱指纹。这一目标是通过将反铁磁性TmFeO_3(Tm铁氧体)中的自旋与定制天线的局部增强太赫兹电场相耦合来实现的。在一皮秒的持续时间内，强烈的太赫兹脉冲突然改变了磁各向异性，并触发了大规模的弹道自旋运动。特征位相翻转、集体自旋共振的不对称分裂和法拉第信号的长寿命偏移是相干自旋转换到相邻势极小值的特征，这与数值模拟一致。可以通过外部偏磁来选择可切换状态。低损耗和天线的亚波长空间清晰度可以促进以太赫兹速率工作的可扩展自旋设备。
Future information technology demands ever-faster, low-loss quantum control. Intense light fields have facilitated milestones along this way, including the induction of novel states of matter(1-3), ballistic acceleration of electrons(4-7) and coherent flipping of the valley pseudospin(8). These dynamics leave unique 'fingerprints', such as characteristic bandgaps or high-order harmonic radiation. The fastest and least dissipative way of switching the technologically most important quantum attribute-the spin-between two states separated by a potential barrier is to trigger an all-coherent precession. Experimental and theoretical studies with picosecond electric and magnetic fields have suggested this possibility(9-11), yet observing the actual spin dynamics has remained out of reach. Here we show that terahertz electromagnetic pulses allow coherent steering of spins over a potential barrier, and we report the corresponding temporal and spectral fingerprints. This goal is achieved by coupling spins in antiferromagnetic TmFeO3 (thulium orthoferrite) with the locally enhanced terahertz electric field of custom-tailored antennas. Within their duration of one picosecond, the intense terahertz pulses abruptly change the magnetic anisotropy and trigger a large-amplitude ballistic spin motion. A characteristic phase flip, an asymmetric splitting of the collective spin resonance and a long-lived offset of the Faraday signal are hallmarks of coherent spin switching into adjacent potential minima, in agreement with numerical simulations. The switchable states can be selected by an external magnetic bias. The low dissipation and the antenna's subwavelength spatial definition could facilitate scalable spin devices operating at terahertz rates.