Cavalieri A L, Müller N, Uphues Th, Yakovlev V S, Baltuska A, Horvath B, Schmidt B, Blümel L, Holzwarth R, Hendel S, Drescher M, Kleineberg U, Echenique P M, Kienberger R, Krausz F, Heinzmann U
Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany.
Nature. 2007 Oct 25;449(7165):1029-32. doi: 10.1038/nature06229.
Comprehensive knowledge of the dynamic behaviour of electrons in condensed-matter systems is pertinent to the development of many modern technologies, such as semiconductor and molecular electronics, optoelectronics, information processing and photovoltaics. Yet it remains challenging to probe electronic processes, many of which take place in the attosecond (1 as = 10(-18) s) regime. In contrast, atomic motion occurs on the femtosecond (1 fs = 10(-15) s) timescale and has been mapped in solids in real time using femtosecond X-ray sources. Here we extend the attosecond techniques previously used to study isolated atoms in the gas phase to observe electron motion in condensed-matter systems and on surfaces in real time. We demonstrate our ability to obtain direct time-domain access to charge dynamics with attosecond resolution by probing photoelectron emission from single-crystal tungsten. Our data reveal a delay of approximately 100 attoseconds between the emission of photoelectrons that originate from localized core states of the metal, and those that are freed from delocalized conduction-band states. These results illustrate that attosecond metrology constitutes a powerful tool for exploring not only gas-phase systems, but also fundamental electronic processes occurring on the attosecond timescale in condensed-matter systems and on surfaces.
全面了解凝聚态物质系统中电子的动态行为，对于许多现代技术的发展至关重要，比如半导体与分子电子学、光电子学、信息处理以及光伏技术等。然而，探测电子过程仍然具有挑战性，其中许多过程发生在阿秒（1阿秒 = 10⁻¹⁸秒）尺度。相比之下，原子运动发生在飞秒（1飞秒 = 10⁻¹⁵秒）时间尺度上，并且已经利用飞秒X射线源在固体中实时绘制出其运动情况。在此，我们将先前用于研究气相中孤立原子的阿秒技术进行拓展，以实时观测凝聚态物质系统以及表面上的电子运动。我们通过探测单晶钨的光电子发射，展示了以阿秒分辨率直接在时域获取电荷动力学信息的能力。我们的数据揭示，源自金属局域核心态的光电子发射与那些从离域导带态中逸出的光电子发射之间存在大约100阿秒的延迟。这些结果表明，阿秒计量学不仅是探索气相系统的有力工具，也是研究凝聚态物质系统以及表面上阿秒时间尺度发生的基本电子过程的有力工具。
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