Boundary-induced violation of the Dirac fermion parity and its signatures in local and global tunneling spectra of graphene

TL;DR

This paper investigates how boundary-induced breaking of Dirac fermion parity in graphene affects edge states and tunneling spectra, revealing particle-hole asymmetry and proposing a device with nonlinear conductance.

Contribution

It demonstrates the impact of boundary conditions on Dirac fermion parity in graphene and links this to observable tunneling spectra and potential device applications.

Findings

Edge states exhibit particle-hole asymmetry due to parity violation.

Zigzag edges induce a polarization in edge states similar to spin polarization.

Proposed a graphene tunneling device with nonlinear conductance characteristics.

Abstract

Extended defects in graphene, such as linear edges, break the translational invariance and can also have an impact on the symmetries specific to massless Dirac-like quasiparticles in this material. The paper examines the consequences of a broken Dirac fermion parity in the framework of the effective boundary conditions varying from the Berry-Mondragon mass confinement to a zigzag edge. The parity breaking reflects the structural sublattice asymmetry of zigzag-type edges and is closely related to the previously predicted time-reversal symmetric edge states. We calculate the local and global densities of the edge states and show that they carry a specific polarization, resembling, to some extent, that of spin-polarized materials. The lack of the parity leads to a nonanalytical particle-hole asymmetry in the edge-state properties. We use our findings to interpret recently observed tunneling spectra in zigzag-terminated graphene. We also propose a graphene-based tunneling device where the particle-hole asymmetric edge states result in a strongly nonlinear conductance-voltage characteristics, which could be used to manipulate the tunneling transport.