Reversible modifications of linear dispersion - graphene between boron nitride monolayers

Electronic properties of the graphene layer sandwiched between two hexagonal boron nitride sheets have been studied using the first-principles calculations and the minimal tight-binding model. It is shown that for the ABC-stacked structure in the absence of external field the bands are linear in the vicinity of the Dirac points as in the case of single-layer graphene. For certain atomic configuration, the electric field effect allows opening of a band gap of over 230 meV. We believe that this mechanism of energy gap tuning could significantly improve the characteristics of graphene-based field-effect transistors and pave the way for future electronic applications.Comment: 5 pages, v2 with slightly modified introduction and summar

QED2+1 in graphene: symmetries of Dirac equation in 2+1 dimensions

It is well-known that the tight-binding Hamiltonian of graphene describes the low-energy excitations that appear to be massless chiral Dirac fermions. Thus, in the continuum limit one can analyze the crystal properties using the formalism of quantum electrodynamics in 2+1 dimensions (QED2+1) which provides the opportunity to verify the high energy physics phenomena in the condensed matter system. We study the symmetry properties of 2+1-dimensional Dirac equation, both in the non-interacting case and in the case with constant uniform magnetic field included in the model. The maximal symmetry group of the massless Dirac equation is considered by putting it in the Jordan block form and determining the algebra of operators leaving invariant the subspace of solutions. It is shown that the resulting symmetry operators expressed in terms of Dirac matrices cannot be described exclusively in terms of gamma matrices (and their products) entering the corresponding Dirac equation. It is a consequence of the reducibility of the considered representation in contrast to the 3+1-dimensional case. Symmetry algebra is demonstrated to be a direct sum of two gl(2,C) algebras plus an eight-dimensional abelian ideal. Since the matrix structure which determines the rotational symmetry has all required properties of the spin algebra, the pseudospin related to the sublattices (M. Mecklenburg and B. C. Regan, Phys. Rev. Lett. 106, 116803 (2011)) gains the character of the real angular momentum, although the degrees of freedom connected with the electron's spin are not included in the model. This seems to be graphene's analogue of the phenomenon called "spin from isospin" in high energy physics

Ab initio study of the relationship between spontaneous polarization and p-type doping in quasi-freestanding graphene on H-passivated SiC surfaces

Quasi-free standing graphene (QFG) obtained by the intercalation of a hydrogen layer between a SiC surface and the graphene is recognized as an excellent candidate for the development of graphene based technology. In addition, the recent proposal of a direct equivalence between the $p$-type doping typically found for these systems and the spontaneous polarization (SP) associated to the particular SiC polytype, opens the possibility of tuning the number of carriers in the Dirac cones without the need of external gate voltages. However, first principles calculations which could confirm at the atomic scale the effect of the SP are lacking mainly due to the difficulty of combining a bulk property such as the SP with the surface confined graphene doping. Here we develop an approach based on standard density functional theory (DFT) slab calculations in order to quantify the effect of the SP on the QFG doping level. First, we present an accurate scheme to estimate the SPs by exploiting the dependence of the slab's dipole moment with its thickness. Next, and in order to circumvent the DFT shortcomings associated to polar slab geometries, a double gold layer is attached at the C-terminated bottom of the slab which introduces a metal induced gap state that pins the chemical potential inside the gap thus allowing a meaningful comparison of the QFG dopings among different polytypes. Furthermore, the slab dipole can be removed after adjusting the Au-Au interlayer distances. Our results confirm that the SP does indeed induce a substantial p-doping of the Dirac cones which can be as large as a few hundreds of meV depending on the hexagonality of the polytype. The evolution of the doping with the slab thickness reveals that several tens of SiC bilayers are required to effectively remove the depolarization field and recover the macroscopic regime whereby the graphene doping should equal the SP

THE DRINKING PATTERNS OF AMERICAN AND POLISH UNIVERSITY STUDENTS: A CROSS-NATIONAL STUDY

This is the post-print version of an article published in Drug and Alcohol Dependence located at http://www.journals.elsevier.com/drug-and-alcohol-dependence/. No DOI is listed for this article.Other research PUBLICATIONS and PAPERS on university students drinking, drug use and health concerns and behaviors can be found at: https://scholarworks.iu.edu/dspace/handle/2022/17130/browse?type=title; https://scholarworks.iu.edu/dspace/handle/2022/17127/browse?type=title and https://scholarworks.iu.edu/dspace/handle/2022/17124/browse?type=title. Further information about the questionnaire, calculations, and the original data base used can be found in the following item records within IUScholarworks repository. Details about the reliability and validity of the SAQ are found at: http://hdl.handle.net/2022/17337; http://hdl.handle.net/2022/17154; http://hdl.handle.net/2022/17181. The classic 1975 copy of the SAQ is found at http://hdl.handle.net/2022/17153. ALL QUESTIONNAIRES developed by Engs are found in the repository at: https://scholarworks.iu.edu/dspace/handle/2022/17141/browse?type=dateissuedA study of 3375 American and 1408 Polish university students was accomplished to test the hypotheses that cultural differences influence drinking patterns and beverage preferences between countries. Using the same questionnaire in both samples, the results revealed that significantly (p < .001) more drinks per week were consumed by both Polish male (24.9) and female (15.2) students compared to American male (15.0) and female (7.6) students. Significantly (p < .001) more wine was consumed by Polish (8.7) compared to the American (0.8) students. American female students consumed more beer than Polish female students. There was no difference between beer and spirits consumption between American and Polish males and Polish students in latter school years consumed more alcohol compared to students in the first years of school. It was concluded that the samples of students in this study reflected their cultures in terms of drinking patterns and beverage preference