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illustration

Angle-resolved photoemission spectroscopy (ARPES)

experiments: Peter Johnson, Nader Zaki
material growth: Cedomir Petrovic, Qianheng Du
theory: Sangkook Choi, Walber de Brito

ARPES measures the electronic band structure of materials by analysing the angle and the kinetic energy of photoemitted electrons. We utilize ultra-violet photon sources including UV laser, UV inert gas lamps, and synchrotron radiation to photoemit electrons from a material of interest in order to deduce its inherent electronic states. In contrast to atoms with a finite number of discrete occupied states, solid materials typically contain ~1023 atoms/cm3, and thus nearly a continues range of occupied states, that can be categorized into energy bands with energy dispersion E(k) in the reciprocal space of a periodic crystal. Incident ultra-violet photons knock out electrons with defined energies at different emission angles, coming from certain bands near the sample surface. By measuring the angle and kinetic energy of these photoemitted electrons, typically by way of a hemispherical analyzer, the electronic states at different k-points and energies can be determined. In addition to studying the electronic structure within this free- or single-particle approximation, ARPES also allows probing for the presence of many-body effects, such as electron-phonon coupling.

For Comscope we are validating an assortment of calculations that are carried out with Comsuite, our in-house developed simulation software suite for strongly correlated materials. In particular, we provide, electronic band structures, selection rules, and in-plane/out-of-plane electronic state components.

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Laue alignment of FeSb2 along its long lattice axis. Sample alignment is critical for ARPES measurements on true 3D (i.e. non-layered) crystals such as FeSb2. Laue has been performed at the Inter-science facility (ISB) at BNL. XPS performed at the Advanced Photon Source, beamline 29-ID-C.

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High photon energy spectroscopy (XPS) of FeSb2 revealing the presence of carbon contamination. Removal of this carbon contamination is important for surface sensitive spectroscopic techniques such as ARPES. XPS has been performed at the Advanced Photon Source, beamline 29-ID-C.

One of the materials of great interest to Comscope is the extraordinary thermoelectric material FeSb2, which has the highest power factor at low temperatures achieved so far. However, this material has proven to be challenging to probe with ARPES. We are now following a new avenue in which we will utilize surface science techniques, available at the Center for Functional Nanomaterials (CFN) at BNL, to determine a recipe for preparing clean and atomically ordered surfaces appropriate for ARPES. Besides, we have also studied another related material of interest, FeCr2, which is more amenable to ARPES studies. Preliminary results have already helped our theoretical collaborators in debugging their codes.    

Related Publications

Cuprate phase diagram and the influence of nanoscale inhomogeneities.
N. Zaki, H.-B. Yang, J. D. Rameau, P. D. Johnson, H. Claus, and D. G. Hinks,
Phys. Rev. B 96, 195163 (2017)