Visualizing quantum spin phenomena through spin-resolving Momentum Microscopy

Ying-Jiun Chen^1,2*, Christian Tusche^1,2

¹Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich GmbH, Jülich, Germany
²Fakultät für Physik, Universität Duisburg-Essen, Duisburg, Germany

* Presenter:Ying-Jiun Chen, email:yi.chen@fz-juelich.de

As a fundamental quantum mechanical property, the spin of the electron plays an important role in the description of electronic states in solids. Through inherently spin dependent interactions like spin-orbit coupling or exchange interaction, the electron spin manifests in many tangible phenomena, such as ferromagnetism, superconductivity, and new topological states of matter. Therefore, a complete photoemission experiment not only aims towards characterizing electron states with respect to their binding energy and crystal momentum, but also with respect to the spin degree of freedom within the full Brillouin zone.

By utilizing state-of-art spin-resolving momentum microscopy as a versatile probe [1-3], in this talk we demonstrate its application to recent questions of advanced spin dependent phenomena in solids, ranging from topological heavy metals [4] to ultrathin hybrid magnets [5]. The direct observation of the quantum-mechanical superposition of different spin states in a topological material will be shown. Spin mixing here is a strongly non-local operator, with a pronounced wave-vector dependence of the respective quantum states. Contrary to previous expectation, we have discovered that the topological Dirac states exhibit completely different spin mixing when spin quantization axis is changed with respect to the symmetry planes of the crystal. Moreover, we will show that an atomically thin magnet can be prepared such that the Fermi surface undergoes a topological transition with discontinuities that need to be bridged by open-loop Fermi arcs, giving evidence for a conceptually new type of mixed topology in a 2D magnet. In addition to unveiling full spin-orbital textures, simultaneous changes in the measured spin-resolved Fermi-surface topology under broken fundamental symmetries will be addressed.

References
[1] C. Tusche, A. Krasyuk, J. Kirschner, Ultramicroscopy 159, p. 520 (2015)
[2] C. Tusche, Y.J. Chen, C.M. Schneider, and J. Kirschner, Ultramicroscopy, 206, p.112815 (2019)
[3] C. Tusche, Y.J. Chen, L. Plucinski and C.M. Schneider, e-J. Surf. Sci. Nanotechnol., 18, pp.48-56 (2020).
[4] Y.J. Chen, M. Hoffmann, B. Zimmermann et al. Commun. Phys. 4, 179 (2021)
[5] Y.J. Chen, J.P. Hanke, M. Hoffmann et al. Nat. Commun. 13, 5309 (2022)

Keywords: spin-orbit coupling, magnetism, topology, Momentum Microscopy