Band structure evolution during the ultrafast ferromagnetic-paramagnetic phase transition in cobalt.
Band structure evolution during the ultrafast ferromagnetic-paramagnetic phase transition in cobalt.
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DOI：
10.1126/sciadv.1602094
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发表时间：
2017-03
期刊：
影响因子：
13.6
通讯作者：
Mathias S
中科院分区：
文献类型：
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作者：
Eich S;Plötzing M;Rollinger M;Emmerich S;Adam R;Chen C;Kapteyn HC;Murnane MM;Plucinski L;Steil D;Stadtmüller B;Cinchetti M;Aeschlimann M;Schneider CM;Mathias S
利用自旋和时间分辨的XUV光电子能谱，研究人员监测了Co在相变过程中的能带结构演化。简单铁磁体Fe、Co和Ni在其众所周知的铁磁-顺磁相变期间的电子能带结构的演化已经争论了几十年，到目前为止还没有明确甚至矛盾的实验观察。利用时间和自旋分辨的光电子能谱，我们可以制作一部电影，展示在用超短激光脉冲激发后，电子性质在真实的时间内如何变化。这使我们能够监测钴的自旋分辨电子能带结构的第一次大的瞬态变化。我们发现，磁化的损失不仅发现周围的费米能级，在那里的状态受到激光激发，但也达到更深的电子带。我们发现铁磁-顺磁相变不能用自旋极化带的交换分裂的损失来解释，而是在激发后显示出快速的带镜像，这是一个非常有效的超快磁振子产生的明显特征。我们的研究结果有助于理解这些看似简单的铁磁系统中的能带结构形成，并给出了与飞秒退磁相关的瞬态过程的第一个明确证据。
Using spin- and time-resolved XUV photoemission, researchers monitor the band structure evolution of Co during its phase transition. The evolution of the electronic band structure of the simple ferromagnets Fe, Co, and Ni during their well-known ferromagnetic-paramagnetic phase transition has been under debate for decades, with no clear and even contradicting experimental observations so far. Using time- and spin-resolved photoelectron spectroscopy, we can make a movie on how the electronic properties change in real time after excitation with an ultrashort laser pulse. This allows us to monitor large transient changes in the spin-resolved electronic band structure of cobalt for the first time. We show that the loss of magnetization is not only found around the Fermi level, where the states are affected by the laser excitation, but also reaches much deeper into the electronic bands. We find that the ferromagnetic-paramagnetic phase transition cannot be explained by a loss of the exchange splitting of the spin-polarized bands but instead shows rapid band mirroring after the excitation, which is a clear signature of extremely efficient ultrafast magnon generation. Our result helps to understand band structure formation in these seemingly simple ferromagnetic systems and gives first clear evidence of the transient processes relevant to femtosecond demagnetization.