Observation of giant spin-split Fermi-arc with maximal Chern number in the chiral topological semimetal PtGa
Mengyu Yao, Kaustuv Manna, Qun Yang, Alexander Fedorov, Vladimir Voroshnin, B. Valentin Schwarze, Jacob Hornung, S. Chattopadhyay, Zhe Sun, Satya N. Guin, Jochen Wosnitza, Horst Borrmann, Chandra Shekhar, Nitesh Kumar, Jörg Fink, Yan Sun, Claudia Felser
Abstract
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.