arXiv subjects

Marijan Šunjić

Publications and source records attributed to Marijan Šunjić.

3 recordsLinked to original sources

arXiv2015

Changing character of electronic transitions in graphene: From single particle excitations to plasmons

In this paper we clarify the nature of $π$ and $π+σ$ electron excitations in pristine graphene. We clearly demonstrate the continuous transition from single particle to collective character of such excitations and how screening modifies their dispersion relations. We prove that $π$ and $π+σ$ plasmons do exist in graphene, though occurring only for a particular range of wavevectors and with finite damping rate. The particular attention is paid to compare the theoretical results with available EELS measurements in optical ($\mathrm{Q\approx 0}$) and other ($\mathrm{Q\neq 0}$) limits. The conclusions, based on microscopic numerical results, are confirmed in an approximate analytical approach.

cond-mat.mtrl-sci↗

arXiv2015

Optical absorption and conductivity in quasi-two-dimensional crystals from first principles: Application to graphene

This paper gives a theoretical formulation of the electromagnetic response of the quasi-two-dimensional (Q2D) crystals suitable for investigation of optical activity and polariton modes. The response to external electromagnetic field is described by current-current response tensor $Π_{μν}$ calculated by solving the Dyson equation in the random phase approximation (RPA), where current-current interaction is mediated by the photon propagator $D_{μν}$. The irreducible current-current response tensor $Π^0_{μν}$ is calculated from the {\em ab initio} Kohn-Sham (KS) orbitals. The accuracy of $Π^0_{μν}$ is tested in the long wavelength limit where it gives correct Drude dielectric function and conductivity. The theory is applied to the calculation of optical absorption and conductivity in pristine and doped single layer graphene and successfully compared with previous calculations and measurements.

cond-mat.mes-hall↗

arXiv2013

Core level spectra in XPS of pristine and doped graphene

Spectra of the C1s core hole, created in XPS and screened by electronic excitations in pristine and doped graphene, are calculated and discussed. We find that singular effects in the lineshapes are not possible in the pristine graphene, and their observation should be connected with the doping. However, the structure of the low energy excitation spectrum in the region where the singular behaviour is expected leads to asymmetries in the core hole lineshapes in pristine graphene similar to those in doped graphene. This makes the analysis more complex than in the case of metals and may lead to incorrect or incomplete interpretation of experimental results.

cond-mat.mtrl-sci↗