Induced fractional valley number in graphene with topological defects

We report on the possibility of valley number fractionalization in graphene with a topological defect that is accounted for in Dirac equation by a pseudomagnetic field. The valley number fractionalization is attributable to an imbalance on the number of one particle states in one of the two Dirac points with respect to the other and it is related to the flux of the pseudomagnetic field. We also discuss the analog effect the topological defect might lead in the induced spin polarization of the charge carriers in graphene

Comment on "Effective of the q-deformed pseudoscalar magnetic field on the charge carriers in graphene"

We point out a misleading treatment in a recent paper published in this Journal [J. Math. Phys. (2016) 57, 082105] concerning solutions for the two-dimensional Dirac-Weyl equation with a q-deformed pseudoscalar magnetic barrier. The authors misunderstood the full meaning of the potential and made erroneous calculations, this fact jeopardizes the main results in this system.Comment: 7 pages, 2 figure

Effects of a uniform magnetic field on twisted graphene nanoribbons

In the present work, the relativistic quantum motion of massless fermions in a helicoidal graphene nanoribbon under the influence of a uniform magnetic field is investigated. Considering a uniform magnetic field ($B$) aligned along the axis of helicoid, this problem is explored in the context of Dirac equation in a curved space-time. As this system does not support exact solutions due to considered background, the bound-state solutions and local density of state (LDOS) are obtained numerically by means of the Numerov method. The combined effects of width of the nanoribbon ($D$), length of ribbon ($L$), twist parameter ($\omega$) and $B$ on the equations of motion and local density of states (LDOS) are analyzed and discussed. It is verified that the presence of $B$ produces a constant minimum value of local density of state on the axis of helicoid, which is possible only for values large enough of $\omega$, in contrast to the case for $B=0$ already studied in the literature.Comment: 10 pages, 7 figure

Effects of a Uniform Magnetic Field on Twisted Graphene Nanoribbons

In the present work, the relativistic quantum motion of massless fermions in a helicoidal graphene nanoribbon under the influence of a uniform magnetic field is investigated. Considering a uniform magnetic field (B) aligned along the axis of helicoid, this problem is explored in the context of Dirac equation in a curved space-time. As this system does not support exact solutions due to considered background, the bound-state solutions and local density of states (LDOS) are obtained numerically by means of the Numerov method. The combined effects of width of the nanoribbon (D), length of ribbon (L), twist parameter (ω), and B on the equations of motion and LDOS are analyzed and discussed. It is verified that the presence of B produces a constant minimum value of local density of state on the axis of helicoid, which is possible only for values large enough of ω, in contrast to the case for already studied in the literature

Fractional fermion charges induced by axial-vector and vector gauge potentials and parity anomaly in planar graphenelike structures

We show that fermion charge fractionalization can take place in a recently proposed chiral gauge model for graphene even in the absence of Kekule distortion in the graphene honeycomb lattice. In this model, electrons couple in a chiral way to a pseudomagnetic field with a vortex profile in such a way that it can be used to describe the influences of topological defects, such as disclinations, on the electronic states. We also extend the model by adding the coupling of fermions to an external magnetic field and show that the fermion charge can be fractionalized by means of only gauge potentials. It is shown that the chiral fermion charge can also have fractional value. We also relate the fractionalization of the fermion charge to the parity anomaly in an extended quantum electrodynamics, which involves vector and axial-vector gauge fields.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Boosting Photovoltaic Efficiency in Double Quantum Well Intermediate Band-Solar Cells through Impurity Positioning

The photovoltaic conversion efficiency of a single-intermediate band solar cell that incorporates a double quantum well structure consisting of GaAs/InAs/GaAs/InAs/GaAs embedded in the intrinsic region of conventional p-i-n structure is analyzed. The width of the intermediate band and the solutions for the two lowest energy states has been determined by solving the two-impurities-related Schrodinger equation based on the Numerov method. The position of these impurities determines three distinct cases: the system in the absence of impurities (Case 1), impurities at the center of GaAs quantum barriers (Case 2), and impurities at the center of InAs quantum wells (Case 3). The photovoltaic conversion efficiency has been calculated as a function of the widths L y H of the quantum well structures. The obtained results indicate an improvement in efficiency under the specific conditions of these parameters