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HL: Fachverband Halbleiterphysik

HL 5: Optical Properties I

HL 5.7: Vortrag

Montag, 18. März 2024, 11:15–11:30, EW 561

Excitons in Helium Under Pressure — •Fatema Mohamed¹, Frédéric Pailloux², Marie-Laure David², Laurent Pizzagalli², Lucia Reining¹, and Matteo Gatti¹ — ¹LSI, Ecole Polytechnique, CNRS, Palaiseau, France — ²Institut Pprime, Université de Poitiers, Poitiers, France

The absorption and the electron energy loss spectra of solid helium at different pressures are calculated using a first principles approach based on the Bethe-Salpeter equation of many-body perturbation theory. The results are used to explain the effect of pressure on HCP helium that has been measured by spectroscopy experiments [1,2]. We found a well defined exciton peak, showing linear pressure dependence, both in the peak position and intensity. We calculated the excitonic dispersion of the loss function along the Γ-M direction for momentum transfers beyond the first Brillouin zone. We found strong parabolic-like dispersion of the spectra, dominated by the screened Coulomb interaction. Near Bragg reflection points we found an anomalous angular dependence of the exciton peak, due to the crystal local field effects, analogously to the plasmon in graphite [3].

References:

1- M.-L. David, et al. Appl. Phys. Lett. 98, 171903, 2011.

2- H. K. Mao, et al. Phys. Rev. Lett. 105, 186404, 2010.

3- R. Hambach, et al. Phys. Rev. Lett. 101, 266406, 2008.

Keywords: Helium; Exciton; Pressure; EELS; Absorption