Spin Berry phase in the Fermi arc states

TL;DR

This paper demonstrates that Fermi arc surface states in Weyl semimetals exhibit a spin Berry phase due to spin-to-surface locking, leading to observable effects like zero-energy bound states in magnetic flux tubes.

Contribution

It provides a theoretical derivation of the spin Berry phase in Fermi arc states from a bulk Weyl Hamiltonian and explores its physical consequences.

Findings

Fermi arc states have a finite size energy gap due to spin Berry phase.

Presence of a pi spin Berry phase leads to zero-energy bound states in magnetic flux tubes.

Dislocation lines in bulk systems support 1D chiral modes related to the spin Berry phase.

Abstract

Unusual electronic property of a Weyl semi-metallic nanowire is revealed. Its band dispersion exhibits multiple subbands of partially flat dispersion, originating from the Fermi arc states. Remarkably, the lowest energy flat subbands bear a finite size energy gap, implying that electrons in the Fermi arc surface states are susceptible of the spin Berry phase. This is shown to be a consequence of spin-to-surface locking in the surface electronic states. We verify this behavior and the existence of spin Berry phase in the low-energy effective theory of Fermi arc surface states on a cylindrical nanowire by deriving the latter from a bulk Weyl Hamiltonian. We point out that in any surface state exhibiting a spin Berry phase pi, a zero-energy bound state is formed along a magnetic flux tube of strength, hc/(2e). This effect is highlighted in a surfaceless bulk system pierced by a dislocation line, which shows a 1D chiral mode along the dislocation line.