We study the resonant tunneling effects through double barrier graphene systems (DBGSs). We have considered two types of DBGSs in order to take into account or rule out Klein tunneling effects: (1) the well-known and documented electrostatic-barrier structures (EBSs) created by means of electrostatic probes that act perpendicularly to the graphene sheet; and (2) substrate-barrier structures (SBSs) built sitting the graphene layer on alternating substrates, such as ${\text{SiO}}_2$ and SiC, which are capable of non-open and open an energy bandgap on graphene. The transfer matrix approach is used to obtain the transmittance, linear-regime conductance, and electronic structure for different set of parameters such as electron energy, electron incident angle, barrier, and well widths. Particular attention is paid to the asymmetric characteristics of the DBGSs, as well as to the main differences between Klein and non-Klein tunneling structures. We find that: (1) the transmission properties can be modulated readily changing the energy and angle of the incident electrons, the widths of the well and barrier regions; (2) the linear-regime conductance is easily enhancing, diminishing, and shifted changing from symmetric to asymmetric DBGSs configuration overall in the case of non-Klein tunneling structures; (3) the conductance shows an oscillatory behavior as function of the well width, with peaks that are directly related to the opening and opening-closure of bound-state subbands for EBSs and SBSs, respectively. Finally, it is important to mention that electrostatic DBGSs or substrate DBGSs could be more suitable depending on a specific application, and in the case of non-Klein tunneling structures, they seem possible considering the sophistication of the current epitaxial growth techniques and whenever substrates that open an energy bandgap on graphene, without diminishing the carrier's mobility, be experimentally discovered.

Low-dimensional thermoelectricity opens the possibility of improving the performance and the efficiency of thermoelectric devices by redistributing the electron density of states through the reduction of dimensionality. In this work, we explore this possibility in silicene by reducing its dimensionality through the periodic arrangement of gated electrodes, the so-called gated silicene superlattices. Silicene electrons were described quantum relativistically. The transmission, conductance, and thermoelectric properties were obtained with the transfer matrix method, the Landauer-Büttiker formalism, and the Cutler-Mott formula, respectively. We find that the redistribution of the density of states together with the intrinsic characteristics of silicene, the local bandgap and the large spin-orbit coupling, contribute to the enhancement of the thermoelectric properties. In particular, the Seebeck coefficient and the power factor reach values of a few mV/K and nW/K${}^2$ . These findings in conjunction with the low thermal conductivity of silicene indicate that silicene-based nanostructures could be the basis of more efficient thermoelectric devices.

It is well known that the unavoidable variation of the heights and widths of the barriers (structural disorder) in semiconductor superlattices and superlattices based on two-dimensional materials degrades important physical properties such as the electronic transport and the thermoelectric response. Here, we show that the structural disorder contrary to what is expected improves the magnetoresistive and spin-valleytronic properties of magnetic silicene superlattices. We reach this conclusion by studying the impact of the random variations of the width and strength of the magnetic barriers on the tunneling magnetoresistance and spin-valley polarization. The theoretical treatment is based on a Dirac-like Hamiltonian, the transfer matrix method, and the Landauer-Büttiker formalism to describe silicene electrons, to obtain the transmittance, and to obtain the conductance, respectively. Our results indicate that structural disorder effects improve the magnetoresistance response and the spin-valley polarization by eliminating the conductance oscillations caused by the periodic magnetic modulation as well as by differentiating the response of the conductance for the parallel and antiparallel magnetization configuration. These results could be useful in designing versatile devices with magnetoresistive and spin-valleytronic capabilities. Particularly, magnetic silicene superlattices with moderate structural disorder are more convenient than perfect or nearly perfect ones.