Ab initio study of the electron energy loss function in a graphene-sapphire-graphene composite system

Scientific paper - Original scientific paper

• Author: Vito Despoja; MBZ: 255255
• Author: Tijana Djordjević
• Author: Lazar Karbunar
• Author: Ivan Radović; MBZ: 131345
• Author: Zoran Mišković
• Author's institution: University of Zagreb; Faculty of Science; (Department of Physics)
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract (english)

The propagator of a dynamically screened Coulomb interaction W in a sandwichlike structure consisting of two graphene layers separated by a slab of Al2O3 (or vacuum) is derived from single-layer graphene response functions and by using a local dielectric function for the bulk Al2O3. The response function of graphene is obtained using two approaches within the random phase approximation (RPA): an ab initio method that includes all electronic bands in graphene and a computationally less demanding method based on the massless Dirac fermion (MDF) approximation for the low-energy excitations of electrons in the π bands. The propagator W is used to derive an expression for the effective dielectric function of our sandwich structure, which is relevant for the reflection electron energy loss spectroscopy of its surface. Focusing on the range of frequencies from THz to mid-infrared, special attention is paid to finding an accurate optical limit in the ab initio method, where the response function is expressed in terms of a frequency-dependent conductivity of graphene. It was shown that the optical limit suffices for describing hybridization between the Dirac plasmons in graphene layers and the Fuchs-Kliewer phonons in both surfaces of the Al2O3 slab, and that the spectra obtained from both the ab initio method and the MDF approximation in the optical limit agree perfectly well for wave numbers up to about 0.1 nm−1. Going beyond the optical limit, the agreement between the full ab initio method and the MDF approximation was found to extend to wave numbers up to about 0.3 nm−1 for doped graphene layers with the Fermi energy of 0.2 eV.

• Keywords (english): 2D plasmons; optical phonons; graphene
• Language: english
• Publication type: Scientific paper - Original scientific paper
• Publication status: Published
• Peer review: Peer review - international
• Publication version: Published version
• Journal title: Physical Review B
• Numbering: vol. 96, no. 7, 075433
• p-ISSN: 2469-9950
• e-ISSN: 2469-9969
• DOI: https://doi.org/10.1103/PhysRevB.96.075433
• URN:NBN: urn:nbn:hr:217:585059
• Publication: 2017
• Document URL: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.075433
• Type of resource: Text
• Access conditions: Open access
• Public note: © 2017 American Physical Society. Received 16 June 2017. Published 23 August 2017.
• Created on: 2020-02-29 18:46:06