arXiv subjects

M. Farjam

Publications and source records attributed to M. Farjam.

6 recordsLinked to original sources

arXiv2015

Projection operator approach to unfolding supercell band structures

While the methodology of band structure unfolding has appeared in several publications, the original derivations of the unfolding formulas can be considerably simplified by using the $k$-projection method. In this work, more transparent derivations of unfolded spectral weights are given by using the projection operator approach. A range of illustrative examples are also presented which include finite and random one-dimensional chains, and Kekulé-textured honeycomb lattice.

cond-mat.mtrl-sci↗

arXiv2014

Visualizing influence of point defects on electronic band structure of graphene

The supercell approach enables us to treat the electronic structure of defective crystals, but the calculated energy bands are too complicated to understand or to compare with angle-resolved photoemission spectra because of inevitable zone folding. We discuss how to visualize supercell band structures more effectively by incorporating in them unfolded spectral weights and orbital decompositions. We then apply these ideas to gain a better understanding of the band structure of graphene containing various types of points defects, including nitrogen impurity, hydrogen adsorbate, and vacancy defect, and also the Stone-Wales defect.

cond-mat.mtrl-sci↗

arXiv2011

Effect of hydrogen adsorption on the quasiparticle spectra of graphene

We use the non-interacting tight-binding model to study the effect of isolated hydrogen adsorbates on the quasiparticle spectra of single-layer graphene. Using the Green's function approach, we obtain analytic expressions for the local density of states and the spectral function of hydrogen-doped graphene, which are also numerically evaluated and plotted. Our results are relevant for the interpretation of scanning tunneling microscopy and angle-resolved photoemission spectroscopy data of functionalized graphene.

cond-mat.mes-hall↗

arXiv2010

Uniaxial strain on gapped graphene

We study the effect of uniaxial strain on the electronic band structure of gapped graphene. We consider two types of gapped graphene, one which breaks the symmetry between the two triangular sublattices (staggered model), and another which alternates the bonds on the honeycomb lattice (Kekulé model). In the staggered model, the effect of strains below a critical value is only a shift of the band gap location. In the Kekulé model, as strain is increased, band gap location is initially pinned to a corner of the Brillouin zone while its width diminishes, and after gap closure the location of the contact point begins to shift. Analytic and numerical results are obtained for both the tight-binding and Dirac fermion descriptions of gapped graphene.

cond-mat.mes-hall↗

arXiv2009

Comment on "Band structure engineering of graphene by strain: First-principles calculations"

In their first-principles calculations of the electronic band structure of graphene under uniaxial strain, Gui, Li, and Zhong [Phys. Rev. B \textbf{78}, 075435 (2008)] have found opening of band gaps at the Fermi level. This finding is in conflict with the tight-binding description of graphene which is closed gap for small strains. In this Comment, we present first-principles calculations which refute the claim that strain opens band gaps in graphene.

cond-mat.mtrl-sci↗

arXiv2009

Energy gap opening in submonolayer lithium on graphene: Local density functional and tight-binding calculations

The adsorption of an alkali-metal submonolayer on graphene occupying every third hexagon of the honeycomb lattice in a commensurate $(\sqrt{3}\times\sqrt{3})R30^\circ$ arrangement induces an energy gap in the spectrum of graphene. To exemplify this type of band gap, we present \textit{ab initio} density functional theory calculations of the electronic band structure of C$_6$Li. An examination of the lattice geometry of the compound system shows the possibility that the nearest-neighbor hopping amplitudes have alternating values constructed in a Kekulé-type structure. The band structure of the textured tight-binding model is calculated and shown to reproduce the expected band gap as well as other characteristic degeneracy removals in the spectrum of graphene induced by lithium adsorption. More generally we also deduce the possibility of energy gap opening in periodic metal on graphene compounds C$_x$M if $x$ is a multiple of 3.

cond-mat.mtrl-sci↗