Fig. 1: Spin–momentum locking prototypes and spin texture of Rarita–Schwinger–Weyl fermion in PtGa.
From: Weyl spin-momentum locking in a chiral topological semimetal
a Overview of the prototypical forms of spin–momentum locking (SML) linear in momentum, (left) orthogonal isotropic Rashba SML with Hamiltonian H = kxσy − kyσx, (middle) mixed orthogonal-parallel Dresselhaus SML H = kxσx − kyσy, and (right) isotropic parallel Weyl SML H = kxσx + kyσy for kz = 0. b Calculated three-dimensional spin texture of the two spherical Fermi surfaces formed by the S = 3/2 Rarita–Schwinger–Weyl multifold fermion in PtGa. Both electron pockets are centred at the Γ point. Panels (i-iii) show two-dimensional slices through the three-dimensional Fermi surface, indicating the radial nature of the spin texture along all momentum directions. Sz denotes the out-of-plane component of the calculated spin polarization and the corresponding color coding applies to all three panels. c Illustration of the link between the spin texture of the bulk multifold fermions (green arrows) and the spin texture of the topological Fermi-arcs surface states (orange arrows). Since the Fermi arcs inherit the spin texture of the bulk bands in the kz = 0 plane, their spin texture is orthogonal to their Fermi surface contour.
