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Mapping of the energetically lowest exciton in bulk 1THfS2

Carsten Habenicht, Lorenzo Sponza, Roman Schuster, Martin Knupfer, and Bernd Büchner
Phys. Rev. B 98, 155204 – Published 11 October 2018

Abstract

By combining electron energy-loss spectroscopy and state-of-the-art computational methods, we were able to provide an extensive picture of the excitonic processes in 1THfS2. The results differ significantly from the properties of the more scrutinized group VI semiconducting transition metal dichalcogenides such as MoS2 and WSe2. The measurements revealed a parabolic exciton dispersion for finite momentum q parallel to the ΓK direction which allowed the determination of the effective exciton mass. The dispersion decreases monotonically for momentum exchanges parallel to the ΓM high symmetry line. To gain further insight into the excitation mechanisms, we solved the ab initio Bethe-Salpeter equation for the system. The results matched the experimental loss spectra closely, thereby confirming the excitonic nature of the observed transitions, and produced the momentum-dependent binding energies. The simulations also demonstrated that the excitonic transitions for q||ΓM occur exactly along that particular high symmetry line. For q||ΓK on the other hand, the excitations traverse the Brillouin zone crossing various high symmetry lines. A particular interesting aspect of our findings was that the calculation of the electron probability density revealed that the exciton assumes a six-pointed star-like shape along the real space crystal planes indicating a mixed Frenkel-Wannier character.

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  • Received 3 August 2018
  • Revised 21 September 2018

DOI:https://doi.org/10.1103/PhysRevB.98.155204

©2018 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Carsten Habenicht1,*, Lorenzo Sponza2, Roman Schuster1, Martin Knupfer1, and Bernd Büchner1,3,4

  • 1IFW Dresden, Institute for Solid State Research, Helmholtzstrasse 20, 01069 Dresden, Germany
  • 2LEM UMR 104, ONERA-CNRS, F-92322 Châtillon, France
  • 3Institute of Solid State Physics, Technische Universität Dresden, 01062 Dresden, Germany
  • 4Center for Transport and Devices, Technische Universität Dresden, 01069 Dresden, Germany

  • *c.habenicht@ifw-dresden.de

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Issue

Vol. 98, Iss. 15 — 15 October 2018

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