Gap emission in ultraviolet photoemission experiments

Courths, R.; Wern, H.; Leschik, G.; Hüfner, S.

doi:10.1007/bf01307390

Cited by 14 publications

(6 citation statements)

References 18 publications

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“…In the final-state band gaps the Bloch waves experience additional damping due to elastic scattering from the crystal potential [5,23]. Although this is normally much weaker than the damping due to V i , as in the above example, for materials with exceptionally large final-state band gaps the additional damping can cause notable degradation of the k ⊥ -resolution.…”

Section: A Non-linearity Mechanismmentioning

confidence: 99%

Intrinsic accuracy in 3-dimensional photoemission band mapping

Strocov¹

2003

Journal of Electron Spectroscopy and Related Phenomena

173

143

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Fundamental principles of mapping 3-dimensional quasiparticle dispersions in the valence band using angle-resolved photoemission spectroscopy are discussed. Such mapping is intrinsically limited in accuracy owing to damping of the final states, resulting in equivalent broadening in the surfaceperpendicular wavevector. Mechanisms of the intrinsic accuracy are discussed in depth based on a physically transparent picture involving interplay of the final-and initial-state spectral functions, and illustrated by photoemission simulations and experimental examples. Other interesting effects of 3dimensional dispersions include 'ghost' photoemission peaks outside the Fermi surface and finite peak width at the Fermi level. Finally, optimization of the experiment on the intrinsic accuracy is discussed.

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Section: A Non-linearity Mechanismmentioning

confidence: 99%

Intrinsic accuracy in 3-dimensional photoemission band mapping

Strocov¹

2003

Journal of Electron Spectroscopy and Related Phenomena

173

143

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“…The method inherits thus the ideas of band-gap PE. 19 In contrast to the conventional PE band mapping procedure ͓employing the energy distribution curve ͑EDC͒ mode in the normal emission geometry and varying the photon energy h], our method ͑1͒ utilizes off-normal PE data; ͑2͒ does not depend on the strength of the non-FE effects but rather utilizes them.…”

Section: Introductionmentioning

confidence: 99%

Core-level photoemission study ofGa1−xMnxAs

et al. 1998

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A method of band mapping providing full control of the three-dimensional k is described in detail. Angledependent very-low-energy electron diffraction is applied to determine the photoemission final states along a Brillouin zone symmetry line parallel to the surface; photoemission out of these states is then utilized to map the valence bands in the constant-final-state mode. The method naturally incorporates the non-free-electron and excited-state self-energy effects in the unoccupied band, resulting in an accuracy superior over conventional techniques. Moreover, its intrinsic accuracy is less limited by lifetime broadening. As a practical advantage, the method provides access to a variety of lines in the Brillouin zone using only one crystal surface. We extensively tested the method on Cu. Several new aspects of the electronic structure of this metal are determined, including non-free-electron behavior of unoccupied bands and missing pieces of the valence band.

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“…Since it is based on Einstein's photoelectric effect, it cannot directly probe a material's unoccupied electronic states, but it has nevertheless provided signatures of gaps in the unoccupied states [3][4][5][6]. According to the one-step model [7], some electrons, after absorbing photons, may have energies which lie between two unoccupied bands.…”

mentioning

confidence: 99%

“…Indeed, while other light sources can probe unoccupied states high above the Fermi energy, laser ARPES probes energies between the sample's workfunction and 6-7 eV above the Fermi energy. It is also possible that the improved bulk sensitivity of laser ARPES resolves the final-state gaps more sharply, since it would reduce the role of evanescent surface states [4]. Lastly, the greater momentum resolution of laser ARPES can be used to better resolve the dispersion of the final-state gap, or the final-state gap may be used to resolve the k ⊥ dispersion.…”

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confidence: 99%

Resolving unoccupied electronic states with laser ARPES in bismuth-based cuprate superconductors

et al. 2015

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Angle-resolved photoemission spectroscopy (ARPES) is typically used to study only the occupied electronic band structure of a material. Here we use laser-based ARPES to observe a feature in bismuth-based superconductors that, in contrast, is related to the unoccupied states. Specifically, we observe a dispersive suppression of intensity cutting across the valence band, which, when compared with relativistic one-step calculations, can be traced to two final-state gaps in the bands 6 eV above the Fermi level. This finding opens up possibilities to bring the ultra-high momentum resolution of existing laser-ARPES instruments to the unoccupied electron states. For cases where the finalstate gap is not the object of study, we find that its effects can be made to vanish under certain experimental conditions.Angle-resolved photoemission spectroscopy (ARPES) is a powerful experimental probe that has been used extensively to image the occupied electronic states of materials in an energy-and momentum-resolved manner [1,2]. Since it is based on Einstein's photoelectric effect, it cannot directly probe a material's unoccupied electronic states, but it has nevertheless provided signatures of gaps in the unoccupied states [3][4][5][6]. According to the one-step model [7], some electrons, after absorbing photons, may have energies which lie between two unoccupied bands. We call the space between the unoccupied bands a finalstate gap, although this gap may be confined to a limited momentum range, and disperse within that range. The photoemission intensity of these electrons is suppressed, but not suppressed completely, due to the finite widths of the final states. These finite widths represent the small chance that electrons interacting with the medium, primarily through electron-hole pair creation and plasmonic interaction, will have energy within the final-state gap. Typically, this final-state effect in ARPES is not used to measure unoccupied states, which are instead mapped by inverse photoemission[8] or very-low-energy electron diffraction [5,[9][10][11][12].Here we show that laser-based ARPES [13][14][15], under certain conditions, can be used to map final-state gaps in the electronic states of a material. This method provides the following advantages with respect to standard synchrotron-based ARPES: (a) improved momentum resolution and greater bulk sensitivity, due to the lower photon energy range available in laser-ARPES (6-7 eV)[13], * alanzara@lbl.gov and (b) access to unoccupied electron states closer to the Fermi level.Data are shown for cuprate superconductors Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) and Bi 2 Sr 2−x La x CuO 6 (La-Bi2201) along the Γ-Y direction of the Brillouin zone, using ∼6 eV laser ARPES. In these measurements, a final-state gap can be seen as a line of suppressed intensity that disperses in momentum.When the final-state gap crosses the photoemitted valence band, it creates a distortion 100-140 meV below the Fermi level, depending on the photon energy. A second distortion is seen at 20-50 meV, indicating...

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Gap emission in ultraviolet photoemission experiments

Cited by 14 publications

References 18 publications

Intrinsic accuracy in 3-dimensional photoemission band mapping

Intrinsic accuracy in 3-dimensional photoemission band mapping

Core-level photoemission study ofGa1−xMnxAs

Resolving unoccupied electronic states with laser ARPES in bismuth-based cuprate superconductors

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