  The interplay of photon spin and orbital angular momentum (OAM) in the
optical fiber (1D waveguide) has recently risen to the forefront of quantum
nanophotonics. Here, we introduce the fermionic dual of the optical fiber, the
Dirac wire, which exhibits unique electronic spin and OAM properties arising
from confined solutions of the Dirac equation. The Dirac wires analyzed here
represent cylindrical generalizations of the Jackiw-Rebbi domain wall and the
minimal topological insulator, which are of significant interest in
spintronics. We show the unique longitudinal spin arising from electrons
confined to propagation in a wire, an effect which is fundamentally prohibited
in planar geometries. Our work sheds light on the universal spatial dynamics of
electron spin in confined geometries and the duality between electronic and
photonic spin.
