Electronic properties of bilayer sheets forming moiré patterns

In this article, we report the electronic band structures of hexagonal bilayer systems, specifically, rotated graphene-graphene and boron nitride-boron nitride bilayers, by introducing an angle between the layers and forming new periodic structures, known as moiré patterns. Using a semi-empirical tight-binding approach with a parametrized hopping parameter between the layers, using one orbital per-site approximation, and taking into account nearest-neighbor interactions only, we found he electronic dispersion relations to be around K points in a low energy approximation. Our results show that graphene bilayers exhibit zero band gap for all angles tested in this work. In boron nitride bilayers, the results reveal a tunable bandgap that satisfies the prediction of the bandgap found in one-dimensional diatomic systems presented in the literature.

Complex geometry of space–time motivated by gravity’s rainbow

In this paper, we generalize the formalism of gravity’s rainbow to complex space–time. The resulting geometry depends on the energy of the probe in such a way that the usual real manifold is the low energy approximation of the Planck scale geometry of space–time. So, our formalism agrees with all the observational data about our space–time being real, as at the scale these experiments are preformed, the imaginary part of the geometry is suppressed by Planck energy. However, the imaginary part of the geometry becomes important near the Planck energy, and so it cannot be neglected near the Planck scale. So, the Planck scale geometry of space–time is described by a complex manifold.

Generalized Dirac structure beyond the linear regime in graphene

We show that a generalized Dirac structure survives beyond the linear regime of the low-energy dispersion relations of graphene. A generalized uncertainty principle of the kind compatible with specific quantum gravity scenarios with a fundamental minimal length (here graphene lattice spacing) and Lorentz violation (here the particle/hole asymmetry, the trigonal warping, etc.) is naturally obtained. We then show that the corresponding emergent field theory is a table-top realization of such scenarios, by explicitly computing the third-order Hamiltonian, and giving the general recipe for any order. Remarkably, our results imply that going beyond the low-energy approximation does not spoil the well-known correspondence with analog massless quantum electrodynamics phenomena (as usually believed), but rather it is a way to obtain experimental signatures of quantum-gravity-like corrections to such phenomena.

Vacuons and Quasi-phonons: The Hidden Side of Bogoliubov Collective Excitations

In a series of papers [1, 2, 3], the author exactly diagonalized the truncated Hamiltonian Hc , proposed by Bogoliubov [4, 5], as a low energy approximation for the weakly interacting boson gas. In addition to the well know collective excitations (CEs) resulting from the Bogoliubov Canonic Approximation (BCA) [6, 7], and denoted as quasi-phonons (QPs), the exact eigenstates of Hc exhibit a new kind of CEs (the `hidden side' which the title alludes to), that we denote as vacuons. Those CEs are created/annihilated by adsorp-tion/emission of a quantum of energy twice as large as the activation energy of a QP. Being momentless, they are reminiscent of Cooper pairs of bosons, with opposite moments. The e_ects of the vacuons on the dynamics of the gas are discussed, with their possible exper-imental evidence.

Elastic scattering and breakup reactions with light proton- and neutron-rich exotic nuclei

A microscopic analysis of the optical potentials (OPs) and cross sections of elastic scattering of 8B on 12C, 58Ni, and 208Pb targets at energies 20 < E < 170 MeV and 12,14Be on 12C at 56 MeV/nucleon is carried out. The real part of the OP is calculated by a folding procedure and the imaginary part is obtained on the base of the high-energy approximation (HEA). The density distributions of 8B evaluated within the variational Monte Carlo (VMC) model and the three-cluster model (3CM) are used to construct the potentials. The 14Be densities obtained in the framework of the the generator coordinate method (GCM) are used to calculate the optical potentials, while for the same purpose both the VMC model and GCM densities of 12Be are used. In the hybrid model developed and explored in our previous works, the only free parameters are the depths of the real and imaginary parts of OP obtained by fitting the experimental data. The use of HEA to estimate the imaginary OP at energies just above the Coulomb barrier is discussed. In addition, cluster model, in which 8B consists of a p-halo and the 7Be core, is applied to calculate the breakup cross sections of 8B nucleus on 9Be, 12C, and 197Au targets, as well as momentum distributions of 7Be fragments. A good agreement of the theoretical results with the available experimental data is obtained. It is concluded that the reaction studies performed in this work may provide supplemental information on the internal spatial structure of the proton- and neutron-halo nuclei.