Experimental setup for low-energy laser-based angle resolved photoemission spectroscopy

Koralek, Jake; Douglas, J. F.; Plumb, N. C.; Griffith, Justin; Cundiff, Steven T.; Kapteyn, Henry C.; Murnane, Margaret M.; Dessau, D. S.

doi:10.1063/1.2722413

Cited by 74 publications

(70 citation statements)

References 25 publications

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“…The TSS of Bi 2 Se 3 extends several layers deep into the bulk (about 2-3 nm) and therefore appears in the spectroscopy for a wide range of probing depths. Indeed, enhanced bulk sensitivity at 6-eV photon energy is provided by an order-of-magnitude larger probing depth than at 50-70 eV [27], and similarly at photon energies in the x-ray range. Specifically, our detailed analysis of the initial state identifies the low binding-energy states in Bi 2 Se 3 as mainly arising from different p orbitals of Bi (6p 3 ) and Se (4p 4 ).…”

Section: Discussionmentioning

confidence: 99%

Photoemission ofBi2Se3with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?

et al. 2014

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Topological insulators are characterized by Dirac-cone surface states with electron spins locked perpendicular to their linear momenta. Recent theoretical and experimental work implied that this specific spin texture should enable control of photoelectron spins by circularly polarized light. However, these reports questioned the so far accepted interpretation of spin-resolved photoelectron spectroscopy. We solve this puzzle and show that vacuum ultraviolet photons (50-70 eV) with linear or circular polarization indeed probe the initial-state spin texture of Bi 2 Se 3 while circularly polarized 6-eV low-energy photons flip the electron spins out of plane and reverse their spin polarization, with its sign determined by the light helicity. Our photoemission calculations, taking into account the interplay between the varying probing depth, dipole-selection rules, and spin-dependent scattering effects involving initial and final states, explain these findings and reveal proper conditions for light-induced spin manipulation. Our results pave the way for future applications of topological insulators in optospintronic devices.

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Section: Discussionmentioning

confidence: 99%

Photoemission ofBi2Se3with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?

et al. 2014

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“…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.…”

mentioning

confidence: 99%

“…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.…”

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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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“…[4] these lower orders can serve as an ideal pump pulse for many small molecules of intense theoretical interest with their first absorption band in the VUV. They also can serve as a compact table top source for angle resolved photoemission spectroscopy (ARPES) [5]. Here we demonstrate that by inserting a fluoride window into the path of an HHG beamline, the low orders of an HHG comb can be temporally separated and be used for femtosecond pump probe experiments.…”

mentioning

confidence: 99%

“…The spectrum of odd harmonics produced by intense femtosecond lasers in gas targets is typically divided into a "plateau" regime, where the harmonic yield is comparable from one harmonic to the next, and a "cutoff" regime, where the harmonic yield falls off rapidly with photon energy. Neglected in this description are the first few orders (3,5,7) which are usually much more intense than the plateau harmonics. As demonstrated by Kosma et.…”

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confidence: 99%

Separation of High Order Harmonics with Fluoride Windows

Allison

Tilborg

Wright

et al. 2009

Conference on Lasers and Electro-Optics/International Quantum Electronics Conference

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The lower orders produced in high order harmonic generation can be efficiently temporally separated into monochromatic pulses by propagation in a fluoride window while still preserving their femtosecond pulse duration. We present calculations for MgF 2 , CaF 2 , and LiF windows for the third, fifth, and seventh harmonics of 800 nm. We demonstrate the use of this simple and inexpensive technique in a femtosecond pump/probe experiment using the fifth harmonic.

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Experimental setup for low-energy laser-based angle resolved photoemission spectroscopy

Cited by 74 publications

References 25 publications

Photoemission ofBi2Se3with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?

Photoemission ofBi2Se3with Circularly Polarized Light: Probe of Spin Polarization or Means for Spin Manipulation?

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

Separation of High Order Harmonics with Fluoride Windows

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