Helical Current of Propagating Dirac Electrons and Geometric Coupling to Chiral Environments

TL;DR

This paper reveals that propagating Dirac electrons inherently carry a helical current structure, which enables geometric coupling to chiral environments and results in spin selectivity without relying on spin-orbit interactions.

Contribution

It introduces the concept of intrinsic helical currents in Dirac electrons and demonstrates their role in geometric coupling to chiral environments, independent of orbital angular momentum.

Findings

Dirac electrons carry a real-space helical current.

Helical structure has a definite handedness and persists in evanescent regions.

Chirality-dependent spin selectivity arises from current geometry, not spin-orbit coupling.

Abstract

We show that a propagating Dirac electron with intrinsic spin generically carries a real--space helical conserved current, even in the absence of orbital angular momentum. Using exact Dirac eigenstates in cylindrical confinement, we demonstrate that this helical structure possesses definite handedness, persists into evanescent regions, and is characterized by a geometric helix pitch independent of the longitudinal de~Broglie wavelength. This intrinsic helical geometry enables a local geometric coupling between a propagating electron and a chiral environment, yielding chirality--dependent spin selectivity through current geometry rather than through a spin--orbit coupling term.