Magnons and excitons from Bethe-Salpeter equation and its application to graphene-based magnets
Abstract
With the recent isolation of two-dimensional semiconducting magnetic materials, the theoretical study of spin-flip collective excitations (magnons) along with spin-conserving electron-hole bound pairs (excitons) has become particularly relevant. Describing both types of quasiparticles within the same theoretical framework is possible, in principle, but the well-established many-body formalism for the calculation of excitons, based on the intertwined Bethe-Salpeter and Hedin's equations, is not satisfactory for magnons, since the usual approximations produce a spurious gapped Goldstone mode. Here, we show that excitons and magnons can be computed on the same footing under the same Bethe-Salpeter formalism, while respecting the gapless Goldstone mode for magnons. We demonstrate how this can be achieved through the evaluation of the full Bethe-Salpeter equation, beyond the Tamm-Dancoff approximation in model Hamiltonians. As an example, we apply it to ferromagnetic and antiferromagnetic graphene, faithfully represented by the extended Hubbard model. Our results clarify the roles of on-site and non-local interactions in exciton and magnon appearance and identify consistency requirements relevant to extending the approach to first-principles calculations.
Related
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BibTeX
@misc{chourasia2026magnons,
title = {{Magnons and excitons from Bethe-Salpeter equation and its application to graphene-based magnets}},
author = {Simran Chourasia and Maurício F. C. Martins Quintela and J. J. Palacios},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.32847},
eprint = {2610.32847},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.32847},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Magnons and excitons from Bethe-Salpeter equation and its application to graphene-based magnets
AU - Simran Chourasia
AU - Maurício F. C. Martins Quintela
AU - J. J. Palacios
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.32847
UR - https://arxiv.org/abs/2610.32847
AB - With the recent isolation of two-dimensional semiconducting magnetic materials, the theoretical study of spin-flip collective excitations (magnons) along with spin-conserving electron-hole bound pairs (excitons) has become particularly relevant. Describing both types of quasiparticles within the same theoretical framework is possible, in principle, but the well-established many-body formalism for the calculation of excitons, based on the intertwined Bethe-Salpeter and Hedin's equations, is not satisfactory for magnons, since the usual approximations produce a spurious gapped Goldstone mode. Here, we show that excitons and magnons can be computed on the same footing under the same Bethe-Salpeter formalism, while respecting the gapless Goldstone mode for magnons. We demonstrate how this can be achieved through the evaluation of the full Bethe-Salpeter equation, beyond the Tamm-Dancoff approximation in model Hamiltonians. As an example, we apply it to ferromagnetic and antiferromagnetic graphene, faithfully represented by the extended Hubbard model. Our results clarify the roles of on-site and non-local interactions in exciton and magnon appearance and identify consistency requirements relevant to extending the approach to first-principles calculations.
ER -