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Giant spatial anisotropy of magnon Landau damping in altermagnets

by António T. Costa, João C. G. Henriques, Joaquín Fernández-Rossier

This Submission thread is now published as

Submission summary

Authors (as registered SciPost users): António Costa
Submission information
Preprint Link: scipost_202411_00053v2  (pdf)
Date accepted: March 25, 2025
Date submitted: Feb. 13, 2025, 12:26 p.m.
Submitted by: Costa, António
Submitted to: SciPost Physics
Ontological classification
Academic field: Physics
Specialties:
  • Condensed Matter Physics - Theory
Approaches: Theoretical, Computational

Abstract

Altermagnets are a new class of magnetic materials with zero net magnetization (like antiferromagnets) but spin-split electronic bands (like ferromagnets) over a fraction of reciprocal space. As in antiferromagnets, magnons in altermagnets come in two flavours, that either add one or remove one unit of spin to the $S=0$ ground state. However, in altermagnets these two magnon modes are non-degenerate along some directions in reciprocal space. Here we show that the lifetime of altermagnetic magnons, due to Landau damping caused by coupling to Stoner modes, has a very strong dependence on both flavour and direction. Strikingly, coupling to Stoner modes leads to a complete suppression of magnon propagation along selected spatial directions. This giant anisotropy will impact electronic, spin, and energy transport properties and may be exploited in spintronic applications.

Author indications on fulfilling journal expectations

  • Provide a novel and synergetic link between different research areas.
  • Open a new pathway in an existing or a new research direction, with clear potential for multi-pronged follow-up work
  • Detail a groundbreaking theoretical/experimental/computational discovery
  • Present a breakthrough on a previously-identified and long-standing research stumbling block

Author comments upon resubmission

Dear Editor,

We hereby submit a revised version of our manuscript "Giant spatial anisotropy of magnon Landau damping in altermagnets" for your appreciation. There was a slight change in title to comply with one of the Referee's requests. Other than that, all changes were minor, but certainly improving the manuscript clarity and readability.

Sincerely yours,
António Costa
(for the authors)

List of changes

- Title changed to "Giant spatial anisotropy of magnon Landau damping in altermagnets," indicating explicitly the origin of magnons' finit lifetimes considered in the manuscript.

- The phrase "due to Landau damping caused by coupling to Stoner modes" has been added to the abstract.

- Fig. 1 has new labels to facilitate identification of the different hopping terms (in the previous version the meaning of the various symbols were indicated in the figure caption only).

- "Stoner damping" has been replaced by "Landau damping by Stoner modes" at line 54.

- A more detailed description of the hopping terms in the Hamiltonian has been added after Eq. 1, at lines 65-69.

- A new bibliography reference ([19]) has been added to footnote 1 at page 5.

- A discussion of the energy difference between different magnon flavors has been amended (lines 134-138).

- "Stoner damping" has been replaced by "Landau damping by Stoner modes" at lines 144-145 and at line 210.

- Appendix E has been reformulated for organization and clarity.

Published as SciPost Phys. 18, 125 (2025)

Reports on this Submission

Report #2 by Anonymous (Referee 2) on 2025-3-6 (Invited Report)

Report

This is an important work in the rapidly developing field of altermagnets. It is also quite sophisticated, using a quantum many-body approach required for the complexity of these materials, when compared to the flood of papers using single-particle quantum mechanics formalisms. The authors have improved the manuscript and its explanations/terminology, so it can be now published as is. I would only suggest checking, during proof correction process, all cited arXiv papers and update those have been published since original submission.

Recommendation

Publish (surpasses expectations and criteria for this Journal; among top 10%)

  • validity: high
  • significance: high
  • originality: high
  • clarity: high
  • formatting: good
  • grammar: excellent

Report #1 by Anonymous (Referee 1) on 2025-3-1 (Invited Report)

  • Cite as: Anonymous, Report on arXiv:scipost_202411_00053v2, delivered 2025-03-01, doi: 10.21468/SciPost.Report.10746

Strengths

1- Advance model that could capture most of the microscopic properties of real correlated materials. 2- Accurate description of the microscopic origin of the observed magnon properties of altermagnets. 3- Consideration of a wide range of scenarios such as metallic and insulating phases of altermagnets.

Report

The authors of the study “Giant spatial anisotropy of magnon lifetime in altermagnets”, have investigated magnons in altermagnets and many-body effects on them with special focus on stoner excitations. For this purpose, they have adopted a Hubbard model of altermagnetism that maintains the parametric continuous transition from the metallic phase to the insulating phase altermagnets and includes the important features of altermagnets such as non-relativistic spin splitting band structure as well as the correlation effects. According to their findings, altermagnetism which comes as a result of reducing the symmetry of the lattice gives rise to interesting spatial anisotropy of magnons with unique directionality of the magnon propagation and lifetime in metallic altermagnets. They relate their finding in directionality dependence of magnon excitation and propagation to broken chirality of the two magnon dispersion which is a unique feature of altermagnets. In addition, they show that even when magnons could be excited in a certain direction with well-defined quasiparticle character, they might be highly suppressed at higher energies and wavevectors due to the Stoner excitations. Nonetheless, their findings reveal that magnons in insulating altermagnets agrees very well with linear spin wave theory and therefore the correlation effects are negligible in this type of altermagnets.

Recommendation

Publish (easily meets expectations and criteria for this Journal; among top 50%)

  • validity: high
  • significance: high
  • originality: high
  • clarity: good
  • formatting: good
  • grammar: good

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