  This study aims to investigate the interplay between chiral-induced
spin-orbit coupling along the screw axis and antisymmetric spin-orbit coupling
(ASOC) in the normal plane within a chiral crystal, using both general model
analysis and first-principles simulations of InSeI, a chiral van der Waals
crystal. While chiral molecules of light atoms typically exhibit spin
selectivity only along the screw axis, chiral crystals with heavier atoms can
have strong ASOC effects that influence spin-momentum locking in all
directions. The resulting phase diagram of spin texture shows the potential for
controlling phase transition and flipping spin by reducing symmetry through
surface cleavage, thickness reduction or strain. We also experimentally
synthesized high-quality InSeI crystals of the thermodynamically stable achiral
analogue which showed exposed (110) facets corresponding to single-handed
helices to demonstrate the potential of material realization for
higher-dimensional spin selectivity in the development of spintronic devices.
