Electronic properties of graphene systems under tension

Abstract

We study the effects of strain on the electronic properties and persistent current characteristics of a graphene ring using the Dirac representation. For a slightly deformed graphene ring flake, one obtains sizable pseudomagnetic (gauge) fields that may effectively reduce or enhance locally the applied magnetic flux through the ring. Flux-induced persistent currents in a flat ring have full rotational symmetry throughout the structure; in contrast, we show that currents in the presence of a circularly symmetric deformation are strongly inhomogeneous, due to the underlying symmetries of graphene. This result illustrates the inherent competition between the ‘real’ magnetic field and the ‘pseudo’ field arising from strains, and suggests an alternative way to probe the strength and symmetries of pseudomagnetic fields on graphene systems. We also explored the transport properties of graphene systems (hexagonal zigzag rings and the zigzag nanoribbons) coupled to left and right leads given by semi-infinite zigzag nanoribbons, following the tight-binding approximation. The local and total density of states and conductance are obtained following the Green’s function formalism and real space renormalization techniques. The localization effects on the physical responses of both system were considered as a consequence of the finite-size confnement of the central part of the nanotructures and due to the applied magnetic field and the presence of tension giving origin to pseudofields. For the nanoribbons we have focused on the apparent regions exhibiting trigonal structure occuring due to a superposition of lattice and strain symmetries. The zigzag hexagonal rings present very interesting transport properties when a magnetic fux is considered. The conductance gets double-peaked at low energies, and it is null at certain energy values, suggesting a possible destructive ring resonance. The peculiar null conductance states are pinned at the same energy values independly of the magnetic field intensity. We believe that strain is not able to destroy the constructive and desctructive interference effects of the ring. We highlight that the strain also promotes a change in the energy values in which the conductance is fully suppressed, being possible to use the ring as a dispositive in which the conductance pattern, with open and close modes, provides a simple way of measuring the strength of strain when compared to the unstrained situation.