Angle resolved photoemission from organic semiconductors: orbital imaging beyond the molecular orbital interpretation
Angle resolved photoemission from organic semiconductors: orbital imaging beyond the molecular orbital interpretation
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DOI：
10.1088/1367-2630/16/10/103005
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发表时间：
2014-10-07
影响因子：
3.3
通讯作者：
Kuemmel, S.
中科院分区：
文献类型：
--
作者：
Dauth, M.;Wiessner, M.;Kuemmel, S.
用各种成像技术获得了可以解释为显示分子轨道的迷人图片。其中，角度分辨光发射光谱（ARPES）作为一种特别强大的方法出现了。轨道图像被用来强调分子轨道概念的物理可信度。然而，从光电过程的理论可以看出，成像实验显示的不是分子轨道，而是戴森轨道。后者不是单粒子哈密顿量的特征态，因此不适合通常用分子轨道来简单解释电子结构。因此，在一项理论和实验相结合的研究中，我们检查了基于戴森轨道和基于分子轨道的ARPES解释是否会导致与实验观察尺度相关的差异。我们讨论了一个方案，允许近似计算戴森轨道与适度的计算努力。明确地考虑了电子松弛。比较表明，虽然分子轨道通常是很好的近似戴森轨道，但对光电发射强度的详细理解可能需要超越分子轨道的图像。特别地，我们清楚地观察到吸附半导体分子在ARPES光谱中的Dyson-orbital特征，当这些特征在一个更大的动量范围内记录时，比在早期的实验中。
Fascinating pictures that can be interpreted as showing molecular orbitals have been obtained with various imaging techniques. Among these, angle resolved photoemission spectroscopy (ARPES) has emerged as a particularly powerful method. Orbital images have been used to underline the physical credibility of the molecular orbital concept. However, from the theory of the photoemission process it is evident that imaging experiments do not show molecular orbitals, but Dyson orbitals. The latter are not eigenstates of a single-particle Hamiltonian and thus do not fit into the usual simple interpretation of electronic structure in terms of molecular orbitals. In a combined theoretical and experimental study we thus check whether a Dyson-orbital and a molecular-orbital based interpretation of ARPES lead to differences that are relevant on the experimentally observable scale. We discuss a scheme that allows for approximately calculating Dyson orbitals with moderate computational effort. Electronic relaxation is taken into account explicitly. The comparison reveals that while molecular orbitals are frequently good approximations to Dyson orbitals, a detailed understanding of photoemission intensities may require one to go beyond the molecular orbital picture. In particular we clearly observe signatures of the Dyson-orbital character for an adsorbed semiconductor molecule in ARPES spectra when these are recorded over a larger momentum range than in earlier experiments.