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  • Letter
  • Open Access

Fingerprints of excitonic collective modes in the two-dimensional electron gas

Jakob Wolff1,2,3, Silvana Botti2,3, Lucia Reining3,4, and Matteo Gatti3,4,5

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Phys. Rev. B 114, L231302 – Published 8 October, 2026

DOI: https://doi.org/10.1103/2vyb-gzg9

Abstract

The two-dimensional homogeneous electron gas (2D HEG) is a prototype system of fundamental interest that can be realized experimentally over a wide range of densities. Here, we investigate its collective charge excitations at low densities, using time-dependent density functional theory. We demonstrate that, beyond traditional plasmons, additional collective excitonic modes emerge for a Wigner-Seitz radius larger than rs≈1. These excitonic modes leave characteristic fingerprints in experimentally accessible quantities, namely, asymmetric peak structures in the loss function and very strong Friedel-like oscillations in the static linear density response that increase when the system approaches a regime of instability. Indeed, at low enough densities the collective modes cross the zero energy axis, indicating an instability of the paramagnetic 2D HEG toward the formation of a charge-density-wave phase with excitonic origin. These findings provide valuable insights for the experimental detection of excitonic collective modes in tunable 2D electron systems and contribute to the fundamental understanding of many-body effects in low-density electron gases.

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Phys. Rev. B 114, L231302– Published 8 October, 2026
  • Received 30 October 2025
  • Revised 6 July 2026
  • Accepted 8 September 2026
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