Exploring the Photoemission Intensity in ARPES: Information Beyond Band Structure

DIPC Seminars

Speaker: Friedrich Reinert (Univ. Wuerzburg, Germany)
When: 2016/04/01
14:00
Place: Donostia International Physics Center (DIPC)
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**Exploring the Photoemission Intensity in ARPES: Information Beyond Band Structure** Friedrich Reinert, Achim Schöll, and Hendrik Bentmann _Universität Würzburg, Experimentelle Physik VII D-97074 Würzburg, Germany reinert@physik.uni-wuerzburg.de_ Angle resolved photoemission spectroscopy (ARPES) has been successfully applied for the investigation of the occupied electronic states in condensed matter physics, with a particular emphasis on the band structure and the line-shape of respective quasi-particle peaks of single-crystalline solids and surfaces. These latter properties are based on the fact that the photoemission spectra represent, under several experimental circumstances and fundamental prerequisites, the spectral function of the photoexcited hole in the (N-1)-system. For the analysis of these data one usually assumes that the photoemission cross- section does not considerably influences the dispersion or the line-shape. However, there are examples where the photoemission cross-section significantly alters the experimental results, but a detailed theoretical description of these effects is in general rather intricate. This contribution shall demonstrate how the dependence of the photoemission intensity can in principle deliver important additional knowledge beyond band dispersion and lineshape. The first example is the so-called "orbital tomography" [1] in which ARPES has been used to reconstruct the orbital shape of adsorbed organic molecules including even subtle details induced by the interaction with the substrate or even by molecular vibrations. Here, the ARPES intensity distribution, given by the photoemission cross-section, is essentially the Fourier transform of the orbital [2]. The second example discusses systems with spin-polarized surface states, as e.g. Rashba systems and topological insulators (TI), for which the intensity dependence can bear important information about the character of the initial state including its spin properties [3]. In the presented model cases relatively simple numerical analyses were applied, instead of using a comprehensive one-step photoemission computation. A crucial role in the experimental intensity analysis plays the recent development of novel analyser systems with an enhanced degree of simultaneity in the data acquisition, which not only allow for an efficient detection of the photoelectron current but also grants access to necessary normalizing and reference information [4]. The combination of these analysers with soft x-ray synchrotron radiation offers high-resolution ARPES investigations of a new quality. REFERENCES 1\. J. Ziroff, F. Forster, A. Schöll, P. Puschnig, F. Reinert, PRL 104, 233004 (2010). 2\. P. Puschnig, S. Berkebile, A. J. Fleming, G. Koller, et al.; SCIENCE 326, 702 (2009). 3\. H. Bentmann, H. Maaß, P. Krüger, F. Reinert, et al.; arxiv.org/abs/1507.04664 4\. C. Tusche, A. Krasyuk, J. Kirschner; Ultramicroscopy 159, 520 (2015)