Parallel spin-momentum locking in a chiral topological semimetal

We present experimental evidence for parallel spin-momentum locking of a multifold fermion in the chiral topological semimetal PtGa. While orthogonal spin-momentum locking, such as Rashba spin-orbit coupling has been studied for decades and inspired a vast number of applications, its natural counterpart, the purely parallel spin-momentum locking over a full Fermi surface, has so far remained elusive in experiments. Recently, chiral topological semimetals that host single- and multifold band crossings have been predicted to realize such parallel locking [1-4]. We use spin- and angle-resolved photoelectron spectroscopy to probe the spin-texture of the topological Fermi-arc surface states in PtGa and find that the spin points orthogonal to the Fermi surface contour for momenta close to the projection of the bulk multifold fermion, which is consistent with parallel spin-momentum locking of the latter [5].

[1] G. Chang, et al., Nat. Mater. 17, 978 (2018).

[2] C. Mera Acosta, et al., Phys. Rev. B 104, 104408 (2021)

[3] W. Tan, et al., Adv Funct Materials, 2208023 (2022).

[4] M. Lin, et. al, arxiv:2204.10113 [cond-mat] (2022).

[5] J. A. Krieger, et. al, arxiv: 2210.08221 [cond-mat] (2022)