Propriedades de transporte em estruturas de grafeno com modulação na velocidade de Fermi

Abstract

A fascinating new branch within the field of Condensed Matter Physics (CMP) was started when graphene - a two-dimensional material composed purely of carbon atoms - was first isolated in 2004. The electronic transport properties of this material differ greatly from conventional semiconductors by linear spectrum for low energies, this causes their charge carriers to behave as massless Dirac fermions, revealing surprising physical properties and potential applications in several areas. In this context, the transport properties of Dirac fermions through two-dimensional structures are investigated in this work. We analyzed the transmission of charge carriers through scattering barriers (single and double) in graphene and graphene nanoribbons. Barriers from electrostatic potential with Fermi velocity modulation are considered. We use the transfer matrix method (TMM) to calculate the coefficient of transmission of the barrier system both for the case of graphene, where we do not consider edge effects, and for graphene nanoribbons that give rise a gap at the Dirac point for a given width of the nanoribbons. A gap term can also be generated in graphene, for example, from deposition on some substrates. We added this effect in the Dirac Hamiltonian for graphene and verified the modifications in the properties of electronic transport. Overall, our results indicate that a reduction in Fermi velocity within the barrier region may partially suppress the backscattering effect resulting from the electrostatic potential, but does not affect the maximum transmission of normal incidence of charge carriers in the barrier region - Klein tunneling. This maximum incidence of normal incidence is a characteristic of Dirac fermions and can be suppressed with consideration of the term of gap in both graphene and nanoribbons. In addition, conductance and Fano factor calculations were also investigated, evidencing the possibility of manipulation of the transport properties in structures based on graphene by modulating the Fermi velocity in low energy regions. The results presented for Fermi velocity modulation in graphene nanostructures can open new routes for the manipulation of quantum transport in low dimensional systems and can be explored in the development of nanoelectronic devices.