Plasmon properties and hybridization effects in silicene

C. Vacacela Gomez, M. Pisarra, M. Gravina, P. Riccardi, and A. Sindona
Phys. Rev. B 95, 085419 – Published 13 February 2017

Abstract

The plasmonic character of monolayer silicene is investigated by time-dependent density functional theory in the random phase approximation. Both the intrinsic (undoped) and several extrinsic (carrier doped or gated) conditions are explored by simulating injection of a probe particle (i.e., an electron or a photon) of energy below 20 eV and in-plane momentum smaller than 1.1Å1. The energy-loss function of the system is analyzed, with particular reference to its induced charge-density fluctuations, i.e., plasmon resonances and corresponding dispersions, occurring in the investigated energy-momentum region. At energies larger than 1.5 eV, two intrinsic interband modes are detected and characterized. The first one is a hybridized π-like plasmon, which is assisted by competing one-electron processes involving sp2 and sp3 states, and depends on the slightest changes in specific geometric parameters, such as nearest-neighbor atomic distance and buckling constant. The second one is a more conventional πσ plasmon, which is more intense than the π-like plasmon and more affected by one-electron processes involving the σ bands with respect to the analogous collective oscillation in monolayer graphene. At energies below 1 eV, two extrinsic intraband modes are predicted to occur, which are generated by distinct types of Dirac electrons (associated with different Fermi velocities at the so-called Dirac points). The most intense of them is a two-dimensional plasmon, having an energy-momentum dispersion that resembles that of a two-dimensional electron gas. The other is an acoustic plasmon that occurs for specific momentum directions and competes with the two-dimensional plasmon at mid-infrared energies. The strong anisotropic character of this mode cannot be explained in terms of the widely used Dirac-cone approximation. As in mono-, bi-, and few-layer graphene, the extrinsic oscillations of silicene are highly sensitive to the concentration of injected or ejected charge carriers. More importantly, the two-dimensional and acoustic plasmons appear to be a signature of the honeycomb lattice, independently of the chemistry of the group-IV elements and the details of the unit-cell geometry.

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  • Received 12 October 2016
  • Revised 19 January 2017

DOI:https://doi.org/10.1103/PhysRevB.95.085419

©2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

C. Vacacela Gomez1,2, M. Pisarra3, M. Gravina1,2, P. Riccardi1,2, and A. Sindona1,2,*

  • 1Dipartmento di Fisica, Università della Calabria, Via P. Bucci, Cubo 30C, I-87036 Rende (CS), Italy
  • 2INFN, sezione LNF, Gruppo collegato di Cosenza, Cubo 31C, I-87036 Rende (CS), Italy
  • 3Departamento de Química, Universidad Autónoma de Madrid, c/ Fco. Tomás y Valiente 7 (Módulo 13), E-28049 Madrid, Spain

  • *antonello.sindona@fis.unical.it

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Issue

Vol. 95, Iss. 8 — 15 February 2017

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