Unimpeded tunneling in graphene nanoribbons

TL;DR

This paper investigates Klein tunneling in zigzag and anti-zigzag graphene nanoribbons, revealing that perfect transmission is governed by pseudo-parity conservation rather than pseudo-spin, and introduces a model that aligns with tight-binding results.

Contribution

The study introduces a pseudo-parity operator to accurately describe Klein tunneling in graphene nanoribbons, resolving limitations of the Dirac equation approach.

Findings

Klein tunneling relates to pseudo-parity conservation.

Perfect transmission occurs at the ribbon center, not head-on incidence.

Pseudo-parity projection explains chirality in nanoribbons.

Abstract

We studied the Klein paradox in zigzag (ZNR) and anti-zigzag (AZNR) graphene nanoribbons. Due to the fact that ZNR (the number of lattice sites across the nanoribbon (N is even) and AZNR (N is odd) configurations are indistinguishable when treated by the Dirac equation, we supplemented the model with a pseudo-parity operator whose eigenvalues correctly depend on the sublattice wavefunctions for the number of carbon atoms across the ribbon, in agreement with the tight-binding model. We have shown that the Klein tunneling in zigzag nanoribbons is related to conservation of the pseudo-parity rather than pseudo-spin in infinite graphene. The perfect transmission in the case of head-on incidence is replaced by perfect transmission at the center of the ribbon and the chirality is interpreted as the projection of the pseudo-parity on momentum at different corners of the Brillouin zone.