Chirality Induced Propagation Velocity Asymmetry

TL;DR

This paper investigates how the interplay of spin, chirality, and spin-orbit interaction in helical nanowires causes a velocity asymmetry between left and right propagating electrons, with implications for chiral-induced spin selectivity.

Contribution

It introduces a microscopic tight-binding model that accounts for spin-orbit interaction and derives the spin-dependent continuity equation, revealing velocity asymmetry due to chirality.

Findings

Velocity asymmetry between left and right propagating electrons in chiral nanowires.

The model's applicability to inorganic double-helix SnIP with a ~1.9 eV band gap.

Connection of velocity asymmetry to the chiral-induced spin selectivity (CISS) effect.

Abstract

The spin-dependent propagation of electrons in helical nanowires is investigated. We show that the interplay of spin angular momentum and nanowire chirality, under spin-orbit interaction, lifts the symmetry between left and right propagating electrons, giving rise to a velocity asymmetry. The study is based on a microscopic tight-binding model that takes into account the spin-orbit interaction. The continuity equation for the spin-dependent probability density is derived, including the spin non-conserving terms, and quantum dynamics calculations are performed to obtain the electron propagating dynamics. The calculations are applied to the inorganic double-helix SnIP, a quasi-1D material that constitutes a semiconductor with a band gap of ~ 1.9 eV. The results, nevertheless, have general validity due to symmetry considerations. The relation of the propagation velocity asymmetry with the phenomena ascribed to the chiral-induced spin selectivity (CISS) effect is examined.