A. Mogulkoc

Zone-boundary phonon induced mini band gap formation in graphene

Abstract We investigate the effect of electron– A 1 g phonon coupling on the gapless electronic band dispersion of the pristine graphene. The electron–phonon interaction is introduced through a Kekule-type distortion giving rise to inter-valley scattering between K and K ′ points in graphene. We develop a Frohlich type Hamiltonian within the continuum model in the long-wave length limit. By presenting a fully theoretical analysis, we show that the interaction of charge carriers with the highest frequency zone-boundary phonon mode of A 1 g - symmetry induces a mini band gap at the corners of the two-dimensional Brillouin zone of the graphene in the THz region. Since electron–electron interactions favor this type of lattice distortion, it is expected to be enhanced, and thus its quantitative implications might be measurable in graphene.

Electronic and optical properties of bilayer blue phosphorus

Abstract We investigate the electronic and optical properties of monolayer and stacking dependent bilayer blue phosphorus in the framework of density functional theory (DFT) and tight-binding approximations. We extract the hopping parameters of TB Hamiltonian for monolayer and bilayer blue phosphorus by using the DFT results. The variation of energy band gap with applied external electric field for two different stacks of bilayer blue phosphorus are also shown. We examine the linear response of the systems due to the external electromagnetic radiation in terms of the dielectric functions in the DFT theory. The relatively large electronic band gap and possibility of exfoliation form bulk structure due to weak interlayer coupling, make blue phosphorus an appropriate candidate for future electronic devices.

Boundaries of Subcritical Coulomb Impurity Region in Gapped Graphene

AbstractThe electronic energy spectrum of graphene electron subjected to a homogeneous magnetic field in the presence of a charged Coulomb impurity is studied analytically within two-dimensional Dirac-Weyl picture by using variational approach. The variational scheme we used is just based on utilizing the exact eigenstates of two-dimensional Dirac fermion in the presence of a uniform magnetic field as a basis for determining analytical energy eigenvalues in the presence of an attractive/repulsive charged Coulomb impurity. This approach allows us to determine under which conditions bound state solutions can or can not exist in gapped graphene in the presence of magnetic field. In addition, the effects of uniform magnetic field on the boundaries of subcritical Coulomb impurity region in the massless limit are also analyzed. Our analytical results show that the critical impurity strength decreases with increasing gap/mass parameter, and also that it increases with increasing magnetic field strength. In the massless limit, we investigate that the critical Coulomb coupling strength is independent of magnetic field, and its upper value for the ground-state energy is 0.752.

Variational approach for the effects of periodic modulations on the spectrum of massless Dirac fermion

AbstractIn the variational framework, we study the electronic energy spectrum of massless Dirac fermions of graphene subjected to one-dimensional oscillating magnetic and electrostatic fields centered around a constant uniform static magnetic field. We analyze the influence of the lateral periodic modulations in one direction, created by these oscillating electric and magnetic fields, on Dirac like Landau levels depending on amplitudes and periods of the field modulations. We compare our theoretical results with those found within the framework of non-degenerate perturbation theory. We found that the technique presented here yields energies lower than that obtained by the perturbation calculation, and thus gives more stable solutions for the electronic spectrum of massless Dirac fermion subjected to a magnetic field perpendicular to graphene layer under the influence of additional periodic potentials.

First principle and tight-binding study of strained SnC

Abstract We study the electronic and optical properties of strained single-layer SnC in the density functional theory (DFT) and tight-binding models. We extract the hopping parameters tight-binding Hamiltonian for monolayer SnC by considering the DFT results as a reference point. We also examine the phonon spectra in the scheme of DFT, and analyze the bonding character by using Mulliken bond population. Moreover, we show that the band gap modulation and transition from indirect to direct band gap in the compressive strained SnC. The applied tensile strain reduces the band gap and eventually the semiconductor to semimetal transition occurs for 7.5% of tensile strain. In the framework of tight-binding model, the effect of spin-orbit coupling on energy spectrum are also discussed. We indicate that while tensile strain closes the band gap, spin-orbit gap is still present which is order of ∼ 40 meV at the Γ point. The substrate effect is modeled through a staggered sub-lattice potential in the tight-binding approximation. The optical properties of pristine and strained SnC are also examined in the DFT scheme. We present the modulation of real and imaginary parts of dielectric function under applied strain.

Effect of long-range structural corrugations on magnetotransport properties of phosphorene in tilted magnetic field

Rippling is an inherent quality of two-dimensional materials playing an important role in determining their properties. Here, we study the effect of structural corrugations on the electronic and tr ...

Fosforenin Sürekli Modeli Üzerine Dördüncü Mertebeden Dalga Vektörünün Etkisi

Fosforen siyah fosforun tek tabakali yapisidir. Dusuk enerji fizigi k∙p teorisi cercevesinde surekli model ile tasvir edilebilir. Surekli modelin gecerli oldugu enerji araligi grafendeki ucgensel egrilikte oldugu gibi ek terimler ile artirilabilir. Burada fosforenin siki-bag Hamiltonyeni k 4 mertebesine kadar seri acilarak yeni bir surekli model olusturulmustur. Dorduncu mertebeden yeni model surekli ve siki-bag Hamiltonyenlerinin ozdegerlerinin ortustugu enerji araligini artirmistir. Dahasi dorduncu mertebeden terimin katkisi goz onunde bulundurularak fosforenin Landau seviyeleri incelenmistir. Dorduncu mertebeden terimin dusuk Landau seviyeleri uzerinde goz ardi edilebilir etkiye sahipken, yuksek Landau seviyelerine ihmal edilemeyen katkilar getirir. Bu calismada fosforenin yuk tasiyicilarinin dinamigini daha iyi tasvir eden yeni bir surekli model onerilmistir.