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Author: Hornung, J. ×

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    Splitting of the magnetic monopole pair-creation energy in spin ice
    (Bristol : IOP Publ., 2020) Hornung, J.; Gottschall, T.; Opherden, L.; Antlauf, M.; Schwarz, M.; Kroke, E.; Herrmannsdörfer, T.; Wosnitza, J.
    The thermodynamics in spin-ice systems are governed by emergent magnetic monopole excitations and, until now, the creation of a pair of these topological defects was associated with one specific pair-creation energy. Here, we show that the electric dipole moments inherent to the magnetic monopoles lift the degeneracy of their creation process and lead to a splitting of the pair-creation energy. We consider this finding to extend the model of magnetic relaxation in spin-ice systems and show that an electric dipole interaction in the theoretically estimated order of magnitude leads to a splitting which can explain the controversially discussed discrepancies between the measured temperature dependence of the magnetic relaxation times and previous theory. By applying our extended model to experimental data of, various spin-ice systems, we show its universal applicability and determine a dependence of the electric dipole interaction on the system parameters, which is in accordance with the theoretical model of electric dipole formation. © 2020 The Author(s). Published by IOP Publishing Ltd.
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    Observation of giant spin-split Fermi-arc with maximal Chern number in the chiral topological semimetal PtGa
    (London : Nature Publishing Group, 2020) Yao, M.; Manna, K.; Yang, Q.; Fedorov, A.; Voroshnin, V.; Valentin Schwarze, B.; Hornung, J.; Chattopadhyay, S.; Sun, Z.; Guin, S.N.; Wosnitza, J.; Borrmann, H.; Shekhar, C.; Kumar, N.; Fink, J.; Sun, Y.; Felser, C.
    Non-symmorphic chiral topological crystals host exotic multifold fermions, and their associated Fermi arcs helically wrap around and expand throughout the Brillouin zone between the high-symmetry center and surface-corner momenta. However, Fermi-arc splitting and realization of the theoretically proposed maximal Chern number rely heavily on the spin-orbit coupling (SOC) strength. In the present work, we investigate the topological states of a new chiral crystal, PtGa, which has the strongest SOC among all chiral crystals reported to date. With a comprehensive investigation using high-resolution angle-resolved photoemission spectroscopy, quantum-oscillation measurements, and state-of-the-art ab initio calculations, we report a giant SOC-induced splitting of both Fermi arcs and bulk states. Consequently, this study experimentally confirms the realization of a maximal Chern number equal to ±4 in multifold fermionic systems, thereby providing a platform to observe large-quantized photogalvanic currents in optical experiments.