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Spin, time, and angle resolved photoemission spectroscopy on WTe2

Mauro Fanciulli, Jakub Schusser, Min-I Lee, Zakariae El Youbi, Olivier Heckmann, Maria Christine Richter, Cephise Cacho, Carlo Spezzani, David Bresteau, Jean-François Hergott, Pascal D'Oliveira, Olivier Tcherbakoff, Thierry Ruchon, Jan Minár, and Karol Hricovini
Phys. Rev. Research 2, 013261 – Published 5 March 2020
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  • INTRODUCTION
  • METHODS
  • EXPERIMENTAL RESULTS
  • DISCUSSION
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • Supplemental Material
    References

    Abstract

    We combined a spin resolved photoemission spectrometer with a high-harmonic generation (HHG) laser source in order to perform spin, time, and angle resolved photoemission spectroscopy (STARPES) experiments on the transition metal dichalcogenide bulk WTe2, a possible Weyl type-II semimetal. Measurements at different femtosecond pump-probe delays and comparison with spin resolved one-step photoemission calculations provide insight into the spin polarization of electrons above the Fermi level in the region where Weyl points of WTe2 are expected. We observe a spin accumulation above the Weyl points region, which is consistent with a spin-selective bottleneck effect due to the presence of spin-polarized conelike electronic structure. Our results support the feasibility of STARPES with HHG, which despite being experimentally challenging provides a unique way to study spin dynamics in photoemission.

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    • Received 25 November 2019
    • Accepted 29 January 2020

    DOI:https://doi.org/10.1103/PhysRevResearch.2.013261

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Physical Systems
    Electronic structureTransition metal dichalcogenidesWeyl semimetal
    1. Techniques
    High-harmonic generationKorringa-Kohn-Rostoker methodSpin-resolved photoemission spectroscopyTime & angle resolved photoemission spectroscopy
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Mauro Fanciulli1,2,*, Jakub Schusser1,2,3, Min-I Lee1,2, Zakariae El Youbi1,2,4, Olivier Heckmann1,2, Maria Christine Richter1,2, Cephise Cacho4, Carlo Spezzani5, David Bresteau2, Jean-François Hergott2, Pascal D'Oliveira2, Olivier Tcherbakoff2, Thierry Ruchon2, Jan Minár3, and Karol Hricovini1,2

    • 1Laboratoire de Physique des Matériaux et Surfaces, CY Cergy Paris Université, 95031 Cergy-Pontoise, France
    • 2Université Paris-Saclay, CEA, CNRS, LIDYL, 91191 Gif-sur-Yvette, France
    • 3New Technologies-Research Center, University of West Bohemia, 30614 Pilsen, Czech Republic
    • 4Diamond Light Source, Harwell Campus, OX110DE Didcot, United Kingdom
    • 5Elettra-Sincrotrone Trieste, 34149 Basovizza, Italy

    • *Corresponding author: mauro.fanciulli@u-cergy.fr

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    Vol. 2, Iss. 1 — March - May 2020

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    • Figure 1
      Figure 1

      (a) Schematics of the Fermi surface of WTe2, with a bulk hole pocket (hP) and electron pocket (eP) in black, and a surface state (SS) in red. The region where WPs are expected is shown in green. The hemispherical analyzer (HA) slit direction, the spin quantization axis α̂ in the xy plane and the angular resolution (blue circle) of spin-resolved data of Fig. 2 are shown. (b) CEMs measured with hν=35.65 eV for two energies, EF (left) and 400 meV above (right), in the situation without pump (top) and 100 fs after a pump pulse (bottom). (c) Integrated intensity in the angular range shown by the blue rectangle in (b) and an energy range between EF and 500 meV above it.

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    • Figure 2
      Figure 2

      (a) I↑ (full) and I↓ (dotted) spin channels for three time delays. (b) Difference between total intensity after and before the pump. (c) Spin polarization along α̂. The calculated spin polarization with SPR-KKR in similar conditions as experimental ones is also shown. Highlighted areas are discussed in the text. (d) SPR-KKR calculations for I↑ and I↓ channels and their sum. The pump photon energy and the six energy regions considered in Fig. 3 are shown.

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    • Figure 3
      Figure 3

      [(a) and (b)] SPR-KKR bandmap projected on α̂ along ΓX¯ for I↓ and I↑ channels, respectively. The green circle highlights the WPs region. Dotted blue lines indicate the experimental angular resolution (note that ky≠0 in the measurement). (c) Measured spin polarization at three time delays integrated in energy over each of the six regions of Fig. 2. (d) Cartoon of the accumulation of spin down electrons above the WPs region.

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    • Figure 4
      Figure 4

      (a) Spin resolved initial state Bloch spectral function at the kz point probed by hν=35.65 eV [11] and (b) corresponding SPR-KKR photoemission calculation, for a CEM at 55 meV above EF. The spin quantization axis is α̂.

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