RESUMO
Gaussian and Gaussian-related structures are quite attractive due to its versatility to modulate the electronic transport, including its possibility as electron filters. Here, we show that these non-conventional profiles are not the exception when dealing with Fermi velocity barriers in monolayer graphene. In particular, we show that Gaussian Fermi velocity graphene barriers (G-FVGBs) and Gaussian-pulsed-like Fermi velocity graphene superlattices (GPL-FVGSLs) can serve as electron band-pass filters and oscillating conductance structures. We reach this conclusion by theoretically studying the transmission and transport properties of the mentioned structures. The study is based on the continuum model, the transfer matrix method and the Landauer-Büttiker formalism. We find nearly flat transmission bands or pass bands for G-FVGBs modulable through the system parameters. The pass bands improve as the maximum ratio of Fermi velocities (ξmax) increases, however its omnidirectional range is reduced. These characteristics result in a decaying conductance (integrated transmission) withξmax. The integrated transmission remains practically unaltered with the size of the system due to the saturation of the electron pass band filtering. In the case of GPL-FVGSLs the GPL profile results in regions of high transmission probability that can merge as flat transmission minibands if the pulse fraction and the superlattice parameters are appropriately tuned. The GPL profile also results in conductance (integrated transmission) oscillations that can be multiplied or reduced in number by adjusting the pulse fraction as well as the superlattice parameters.
RESUMO
It is well known that the confinement of matter inside a microcavity can significantly enhance the light-matter interactions. As a result the vacuum fluctuations, induced by virtual photons, can occur in a volume much lower than the free-space diffraction limit. In this work we show that, for a single doped graphene plane inside a microcavity, these enhanced vacuum interactions can produce a significant reduction in the Fermi velocity of the electrons. The effect arises because the energies of the photons are much larger than the energies of the electrons in graphene, which implies that the vacuum exchange interaction is repulsive around the Fermi level. Consequently the quasiparticle Fermi velocity decreases, in contrast with the enhancement obtained in Hartree-Fock. For THz cavities, the reduction is highly localized around the Fermi level, and is practically independent of the carrier density in graphene.