Distinguishing attosecond electron-electron scattering and screening in transition metals
Distinguishing attosecond electron-electron scattering and screening in transition metals
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DOI：
10.1073/pnas.1706466114
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发表时间：
2017-07-03
影响因子：
11.1
通讯作者：
Murnane, Margaret
中科院分区：
文献类型：
--
作者：
Chen, Cong;Tao, Zhensheng;Murnane, Margaret
电子-电子相互作用是材料中最快的过程，发生在飞秒到阿秒的时间尺度上，这取决于材料的电子能带结构和激发能。这种相互作用可以在光诱导过程中发挥主导作用，例如纳米增强等离子体和催化，光收集或相变。然而，迄今为止，还不可能通过实验区分基本的电子相互作用，如散射和屏蔽。在这里，我们使用阿秒脉冲序列来直接测量具有简单和复杂费米表面的不同材料的不同带中的电子-电子相互作用。通过提取与光发射相关的时间延迟，我们发现Cu的d波段的光电子寿命比Ni的相同波段的光电子寿命长100倍。我们将此归因于Ni未填充的d带中电子-电子散射的增强。通过理论建模，我们可以提取出具有简单和复杂费米表面的不同材料在不同波段的电子-电子散射和筛选的贡献。我们的研究结果还表明，筛选对高能光电子（约20 eV）的影响明显小于低能光电子。因此，高能光电子可以作为自旋依赖的电子-电子散射的直接探针而忽略筛选。然后，这可以应用于量化电子相互作用的贡献，并筛选接近费米能级的低能量激发。这里得到的信息为许多量子材料提供了有价值和独特的信息。
Electron-electron interactions are the fastest processes in materials, occurring on femtosecond to attosecond timescales, depending on the electronic band structure of the material and the excitation energy. Such interactions can play a dominant role in light-induced processes such as nano-enhanced plasmonics and catalysis, light harvesting, or phase transitions. However, to date it has not been possible to experimentally distinguish fundamental electron interactions such as scattering and screening. Here, we use sequences of attosecond pulses to directly measure electron-electron interactions in different bands of different materials with both simple and complex Fermi surfaces. By extracting the time delays associated with photoemission we show that the lifetime of photoelectrons from the d band of Cu are longer by similar to 100 as compared with those from the same band of Ni. We attribute this to the enhanced electron-electron scattering in the unfilled d band of Ni. Using theoretical modeling, we can extract the contributions of electron-electron scattering and screening in different bands of different materials with both simple and complex Fermi surfaces. Our results also show that screening influences high-energy photoelectrons (approximate to 20 eV) significantly less than low-energy photoelectrons. As a result, high-energy photoelectrons can serve as a direct probe of spin-dependent electron-electron scattering by neglecting screening. This can then be applied to quantifying the contribution of electron interactions and screening to low-energy excitations near the Fermi level. The information derived here provides valuable and unique information for a host of quantum materials.