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Three-dimensional electron dynamics in PtBi2
The interplay between the Weyl states of trigonal bulk PtBi2 and complex many-body physics at the crystal surface has been the subject of a recent study showing that the surface-confined states associated with the Fermi arcs host superconductivity [1]. The Weyl points occur in conduction band states that are not occupied at room temperature and that therefore cannot be directly probed by traditional methods of angle-resolved photoemission spectroscopy (ARPES). Pump-probe methods are thus needed. Furthermore, to access the states of interest in the three dimensional (3D) Brillouin zone, it is necessary to be able to efficiently scan the photon energy of the probe. We have recently made such measurements at the UK Central Laser Facility’s Artemis Laboratory, which offers a lab-based table-top laser system coupled to a user beamline for high-harmonic generation in a gas jet. The beamline permits short-pulse pump-probe ARPES measurements with pulse width approximately 60 fs, and on-the-fly probe scanning through harmonics in the range 20 – 45 eV.
Pump-probe ARPES measurements present analytical challenges, due the addition of the time dimension to (k||,EB) data sets. The implementation of photon-energy dependence adds yet another dimension, kz, which makes data sets quite large and complex. Added to this is the fact that many modern beamlines, such as the one at Artemis, are now incorporating (x,y) spatial degrees of scanning, polarization dependence, fluence dependence, and more. By implementing an unsupervised “k-means” machine-learning technique, we are able to extract rich, detailed information from high-dimensional data sets, and to compare electron dynamics close to the Weyl points with those in other parts of the Brillouin zone [2].
[1] Kuibarov, et al., Nature 626 (2024), 294. [2] Majchrzak, et al., Phys. Rev. Res. 7 (2025) 013025.