Fanciulli Mauro, Volfová Henrieta, Muff Stefan, Braun Jürgen, Ebert Hubert, Minár Jan, Heinzmann Ulrich, Dil J Hugo
Institut de Physique, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland.
Phys Rev Lett. 2017 Feb 10;118(6):067402. doi: 10.1103/PhysRevLett.118.067402.
After photon absorption, electrons from a dispersive band of a solid require a finite time in the photoemission process before being photoemitted as free particles, in line with recent attosecond-resolved photoemission experiments. According to the Eisenbud-Wigner-Smith model, the time delay is due to a phase shift of different transitions that occur in the process. Such a phase shift is also at the origin of the angular dependent spin polarization of the photoelectron beam, observable in spin degenerate systems without angular momentum transfer by the incident photon. We propose a semiquantitative model which permits us to relate spin and time scales in photoemission from condensed matter targets and to better understand spin- and angle-resolved photoemission spectroscopy (SARPES) experiments on spin degenerate systems. We also present the first experimental determination by SARPES of this time delay in a dispersive band, which is found to be greater than 26 as for electrons emitted from the sp-bulk band of the model system Cu(111).
在光子吸收之后，固体色散带中的电子在光发射过程中需要有限的时间才能作为自由粒子被光发射出来，这与最近的阿秒分辨光发射实验一致。根据艾森布德 - 维格纳 - 史密斯模型，时间延迟是由于该过程中发生的不同跃迁的相移所致。这种相移也是光电子束角度相关自旋极化的起源，在没有入射光子角动量转移的自旋简并系统中可以观察到。我们提出了一个半定量模型，该模型使我们能够关联凝聚态物质靶光发射中的自旋和时间尺度，并更好地理解自旋简并系统的自旋和角分辨光发射光谱（SARPES）实验。我们还展示了通过SARPES对色散带中这种时间延迟的首次实验测定，发现对于从模型系统Cu(111)的sp体带发射的电子，该时间延迟大于26阿秒。
