Vito Despoja

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

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 crystals suitable for investigation of optical activity and polariton modes. The response to external electromagnetic field is described by current-current response tensor Πμν calculated by solving the Dyson equation in the random phase approximation, where current-current interaction is mediated by the photon propagator Dμν. The irreducible current-current response tensor Π0μν is calculated from the ab initio Kohn-Sham orbitals. The accuracy of Π0μν 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.

Quasiparticle spectra and excitons of organic molecules deposited on substrates: G0W0-BSE approach applied to benzene on graphene and metallic substrates

We present an alternative methodology for calculating the quasiparticle energy, energy loss, and optical spectra of a molecule deposited on graphene o

Theory of core-level spectra in x-ray photoemission 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.

Tuning MgB2(0001) surface states through surface termination

V. Despoja,1, 2, ∗ D. J. Mowbray,1, 3 and V. M. Silkin1, 2, 4 1Donostia International Physics Center (DIPC), P. Manuel de Lardizabal, E-20018 San Sebastián, Spain 2Depto. de Fı́sica de Materiales and Centro Mixto CSIC-UPV/EHU, Facultad de Ciencias Quimicas, Universidad del Paı́s Vasco, Apdo. 1072, E-20018 San Sebastián, Spain 3Nano-Bio Spectroscopy Group and ETSF Scientific Development Centre, Depto. Fı́sica de Materiales, Universidad del Paı́s Vasco, Av. Tolosa 72, E-20018 San Sebastián, Spain 4IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao, Spain

Strong two-dimensional plasmon in Li-intercalated hexagonal boron-nitride film with low damping

The field of plasmonics seeks to find materials with an intensive plasmon (large plasmon pole weight) with low Landau, phonon, and other losses (small decay width). In this paper, we propose a new class of materials that show exceptionally good plasmonic properties. These materials consist of van der Waals stacked “plasmon active” layers (atomically thin metallic layers) and “supporting” layers (atomically thin wide band gap insulating layers). One such material that can be experimentally realized—lithium intercalated hexagonal boron-nitride is studied in detail. We show that its 2D plasmon intensity is superior to the intensity of well-studied Dirac plasmon in heavy doped graphene, which is hard to achieve. We also propose a method for computationally very cheap, but accurate analysis of plasmon spectra in such materials, based on one band tight-binding approach and effective background dielectric function.Plasmonics: Intercalated h-BN films support 2D plasmons with low dampingLithium intercalated hexagonal boron nitride (LiB2N2) gives rise to strong 2D plasmons. A team led by V. Despoja at Universidad del Pais Vasco and Zagreb Institute of Physics developed an ab-initio theoretical investigation of a class of materials displaying superior plasmonic properties. These are van der Waals plasmonic metallic layers, in combination with supporting layers that act as wide bandgap insulating materials. In LiB2N2 multilayers, the lithium layer represents the plasmon-active material, whereas two hBN layers are the insulating supporters. In the proposed computational methodology, the optical response of the plasmon-active layer is approximated to a 2D response function, whereas the supporting layers are accounted for by means of an effective background dielectric function. LiB2N2 can support 2D plasmons with an intensity superior to that of Dirac plasmons in heavily doped graphene.