Seminar: 2D materials electronic properties

Prof. Sylvain Latil (CEA researcher fellow, Service de Physique de la Matière Condensée, France)
  • When Apr 30, 2021 from 12:50 PM to 01:50 PM (Europe/Brussels / UTC200)
  • Where Online (Teams)
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Layered hexagonal boron nitride (hBN) belongs to the famous group of 2D materials like
graphene, transition metal dichalcogenides or black phosphorus. In spite hBN is isomorphic to
graphene, it is a wide band gap semiconductor (> 6 eV) which attracts a growing interest for its
strong UV photo-luminescence properties [1]. The optical properties of bulk hBN as well as BN
layers are governed by strong excitonic effects. They have been studied recently, but experiments
are difficult because of the necessity to work in the far UV range [2].
During this seminar, after a short presentation of the general properties of this 2D material, I will
introduce the problematic of excitons in such systems. I will present our tight-binding model
dedicated to the calculation of excitons states in hBN, and show our results in comparison with ab
initio results obtained through many body perturbation theory (GW approximation and Bethe-
Salpeter equation).
In case of the monolayer, a detailed theoretical study of the first excitonic levels, and a
characterization of their binding energies and shape [3] will be presented. Strong deviations from
the usual hydrogenoic model are evidenced due to both lattice effects and the 2D nature of the
screening. In a second time, I will focus on the exciton dispersion rather than the single-particle
band structure to investigate the excitonic properties of the monolayer and of some bulk
polymorphs of hBN, with the intent of disclosing the connections between atomic arrangement,
single-particle band structure and exciton dispersion [4]. At last I will present our theoretical
predictions on optical absorption, including two photons phenomana [5].

References
[1] L. Wirtz et al., Phys. Rev. Lett. 96 126104 (2006)
[2] L. Schué et al., Nanoscale 8 6986 (2016) ; L. Schué et al., Phys Rev Lett 122, 067401 (2019).
[3] T. Galvani et al., Phys. Rev. B 94,125303 (2016)
[4] L. Sponza et al., Phys. Rev. B 98, 125206 (2018)
[5] C. Attaccalite et al., Phys. Rev. B 98, 165126 (2018)