arXiv subjects

Arabinda Nayak

Publications and source records attributed to Arabinda Nayak.

4 recordsLinked to original sources

arXiv2017

Band-gap tuning and optical response of two-dimensional Si$_x$C$_{1-x}$: A first-principles real space study of disordered 2D materials

We present a real-space formulation for calculating the electronic structure and optical conductivity of such random alloys based on the Kubo-Greenwood formalism interfaced with the augmented space recursion (ASR) [A. Mookerjee, J. Phys. C: Solid State Phys. {\bf 6}, 1340 (1973)] formulated with the Tight-binding Linear Muffin-tin Orbitals (TB-LMTO) basis with van Leeuwen-Baerends corrected exchange (vLB) [Singh et al, Phys. Rev B {\bf 93}, 085204, (2016)]. This approach has been used to quantitatively analyze the effect of chemical disorder on the configuration averaged electronic properties and optical response of 2D honeycomb siliphene Si$_{x}$C$_{1-x}$ beyond the usual Dirac-cone approximation. We predicted the quantitative effect of disorder on both the electronic-structure and optical response over a wide energy range, and the results discussed in the light of the available experimental and other theoretical data. Our proposed formalism may open up a facile way for planned band gap engineering in opto-electronic applications.

cond-mat.mtrl-sci↗

arXiv2017

Effect of disorder on the optical response of NiPt and Ni$_3$Pt alloys

In this communication we present a detailed study of the effect of chemical disorder on the optical response of Ni$_{1-x}$Pt$_x$ (0.1$\leq$ x $\leq$0.75) and Ni$_{3(1-x)/3}$Pt$_x$ (0.1$\leq$ x $\leq$0.3). We shall propose a formalism which will combine a Kubo-Greenwood approach with a DFT based tight-binding linear muffin-tin orbitals (TB-LMTO) basis and augmented space recursion (ASR) technique to explicitly incorporate the effect of disorder. We show that chemical disorder has a large impact on optical response of Ni-Pt systems. In ordered Ni-Pt alloys, the optical conductivity peaks are sharp. But as we switch on chemical disorder, the UV peak becomes broadened and its position as a function of composition and disorder carries the signature of a phase transition from NiPt to Ni$_3$Pt with decreasing Pt concentration. Quantitatively this agrees well with Massalski's Ni-Pt phase diagram \cite{massal}. Both ordered NiPt and Ni$_3$Pt have an optical conductivity transition at 4.12 eV. But disordered NiPt has an optical conductivity transition at 3.93 eV. If we decrease the Pt content, it results a chemical phase transition from NiPt to Ni$_3$Pt and shifts the peak position by 1.67 eV to the ultraviolet range at 5.6 eV. There is a significant broadening of UV peak with increasing Pt content due to enhancement of 3d(Ni)-5d(Pt) bonding. Chemical disorder enhances the optical response of NiPt alloys nearly one order of magnitude. Our study also shows the fragile magnetic effect on optical response of disordered Ni$_{1-x}$Pt$_x$ (0.4$<$ x $<$0.6) binary alloys. Our theoretical predictions agree more than reasonably well with both earlier experimental as well as theoretical investigations.

cond-mat.mtrl-sci↗

arXiv2017

Effect of doping on the electronic properties of Graphene and T-graphene : A theoretical approach

In this communication we present together four distinct techniques for the study of electronic structure of solids : the tight-binding linear muffin-tin orbitals (TB-LMTO), the real space and augmented space recursions and the modified exchange-correlation. Using this we investigate the effect of random vacancies on the electronic properties of the carbon hexagonal allotrope, graphene, and the non-hexagonal allotrope, planar T graphene. We have inserted random vacancies at different concentrations, to simulate disorder in pristine graphene and planar T graphene sheets. The resulting disorder, both on-site (diagonal disorder) as well as in the hopping integrals (off-diagonal disorder), introduces sharp peaks in the vicinity of the Dirac point built up from localized states for both hexagonal and non-hexagonal structures. These peaks become resonances with increasing vacancy concentration. We find that in presence of vacancies, graphene-like linear dispersion appears in planar T graphene and the cross points form a loop in the first Brillouin zone similar to buckled T graphene that originates from $π$ and $π$* bands without regular hexagonal symmetry. We also calculate the single-particle relaxation time, $τ(\vec{q})$ of $\vec{q}$ labeled quantum electronic states which originates from scattering due to presence of vacancies, causing quantum level broadening.

cond-mat.mes-hall↗

arXiv2017

Disorder induced lifetime effects in binary disordered systems : a first principles formalism and an application to doped Graphene

In this work the conducting properties of graphene lattice with a particular concentration of defect (5\% and 10\%) has been studied. The real space block recursion method introduced by Haydock et al. has been used in presence of the random distribution of defects in graphene. This Green function based method is found more powerful than the usual reciprocal based methods which need artificial periodicity. Different resonant states appear because of the presence of topological and local defects are studied within the framework of Green function.

cond-mat.mtrl-sci↗