Comment on "Single-parameter quantum charge and spin pumping in armchair graphene nanoribbons" (arXiv:1206.3435v1, by Zhou and Wu)

TL;DR

This paper critically examines Zhou and Wu's recent work on charge and spin pumping in graphene nanoribbons, arguing that their theoretical approach is not applicable to the authors' system due to fundamental differences such as broken time-reversal symmetry.

Contribution

The authors clarify the conceptual differences between their system and Zhou and Wu's, demonstrating that Zhou and Wu's theory cannot be applied to their magnetic lead setup.

Findings

Zhou and Wu's theory is not applicable to magnetic lead systems.

The physical systems considered are fundamentally different.

Zhou and Wu's claims are scientifically unfounded in this context.

Abstract

In their recent submission arXiv:1206.3435v1 Zhou and Wu addressed the charge and spin pumping in an armchair graphene nanoribbon connected to magnetic and/or nonmagnetic leads at zero bias. They used thereby a pumping current formula based on time-reversal symmetry. In their appendix they made, based on their formulas, a number of claims concerning our recent works [K. -H. Ding, Z. -G. Zhu, and J. Berakdar, Phys. Rev. B 84, 115433 (2011)] on the laser modification of the spin-dependent current in an extended graphene monolayer contacted to two magnetic leads under a finite bias. Below we show in detail that the physical system considered by us is conceptually different from that of Zhou and Wu (arXiv:1206.3435v1) and cannot be treated with their theory for fundamental reasons (e.g., the time-reversal symmetry is inherently broken in our case due to the presence of the magnetic leads and the dc current generated by the finite bias). Hence, the statements of Zhou and Wu based on a comparison of their results with ours are scientifically groundless.