SciPost Submission Page
Nonthermal magnetization pathways in photoexcited semiconductors
by Giovanni Marini
Submission summary
| Authors (as registered SciPost users): | Giovanni Marini |
| Submission information | |
|---|---|
| Preprint Link: | https://arxiv.org/abs/2509.18335v1 (pdf) |
| Date submitted: | Sept. 24, 2025, 8:15 a.m. |
| Submitted by: | Giovanni Marini |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approach: | Computational |
Abstract
The stabilization of long-range magnetic order in nominally non-magnetic semiconductors using femtosecond light pulses is an exciting yet experimentally challenging goal. Theoretical studies indicate that certain non-magnetic semiconductors can exhibit transient magnetic instabilities following above-gap laser excitation, but the dynamical pathways leading to these states remain largely unexplored. In this work, I introduce a minimal real-time spin-orbital model and identify the fundamental microscopic mechanisms that enable the emergence of a transient magnetic order. I then discuss the relevance of these findings for real materials employing a phenomenological time-dependent Ginzburg- Landau model. Finally, I analyze the strengths and limitations of current first-principles methodologies for investigating dynamically induced broken- symmetry states in the light of the present results.
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
Current status:
In refereeing
Reports on this Submission
Report
The MS by Marini theoretically explores light-induced magnetic states in initially non-magnetic materials with a combined model Hamiltonian approach, and a GL formulation. The main novel results are in the insight showing that a kicked angular momentum completely suffices to initiate the process of magnetization, and analyzing the contributions of the different interactions to the dynamics. Moreover, the role of relaxation is incorporated and shown to lead to slow dephasing of the magnetic state, which is usually not modeled in TDDFT and ab-initio simulations of ultrafast magnetization.
Overall, I think that the insight obtained in the simple model is extremely interesting, and definitely worthy of publication in scipost. In particular, it might end up motivating novel schemes for optically controlling magnetism, or elucidating the physical mechanism responsible in different systems. Therefore, I strongly support publication after a minor revision addressing the comments below:
1. I think that some of the key results are not sufficiently highlighted in the abstract and introduction currently. The intro is quite long and the context of the main results here is not clearly stated there. Therefore, I think it could be great if the author could emphasize these points. Especially, the novelty in the idea to only kick the electronic angular momentum to simulate the process.
2. It would be great to move some of the technical details, especially the main equations of motion, to the main text. Unless there’s a specific requirement by scipost, it would help to see the equations for the model while analyzing the figures.
3. What is the importance of the type of kick given to L – in terms of intensity, direction, polarization axis?
4. I think some discussion on the limitations of the model used here is still needed – for instance, in TDDFT one includes directly the interaction between light and electrons, while here that is completely neglected and replaced by an angular momentum kick. That captures the main details nicely, but might fail in certain regimes, e.g. if e-e interactions cause a dissipation of the electronic angular momentum, or many other features neglected. Those should be highlighted. Similarly, spin-phonon coupling that could be responsible for several mechanisms of light induced magnetism is not included.
5. It should be explained what kind of relaxation pathways are included here – there are many options, and which are not.
6. Fig. 3 currently doesn’t contribute a whole lot to the text. It might be better to find a more quantitative way to plot the data from the GL model, especially, to compare it directly to the model spin simulations.
7. The long timescale periodic spin dynamics (e.g. in fig 4) seem reminiscent of some magnonic excitation, perhaps also a superposition of magnons. Is that the case? It’s worth discussing.
8. The main idea presented by this paper as I see it is that in order to induce strong control over magnetization, one needs to find a material where laser-L coupling is strong – it’s worth discussing what good options might be.
Overall, I think that the insight obtained in the simple model is extremely interesting, and definitely worthy of publication in scipost. In particular, it might end up motivating novel schemes for optically controlling magnetism, or elucidating the physical mechanism responsible in different systems. Therefore, I strongly support publication after a minor revision addressing the comments below:
1. I think that some of the key results are not sufficiently highlighted in the abstract and introduction currently. The intro is quite long and the context of the main results here is not clearly stated there. Therefore, I think it could be great if the author could emphasize these points. Especially, the novelty in the idea to only kick the electronic angular momentum to simulate the process.
2. It would be great to move some of the technical details, especially the main equations of motion, to the main text. Unless there’s a specific requirement by scipost, it would help to see the equations for the model while analyzing the figures.
3. What is the importance of the type of kick given to L – in terms of intensity, direction, polarization axis?
4. I think some discussion on the limitations of the model used here is still needed – for instance, in TDDFT one includes directly the interaction between light and electrons, while here that is completely neglected and replaced by an angular momentum kick. That captures the main details nicely, but might fail in certain regimes, e.g. if e-e interactions cause a dissipation of the electronic angular momentum, or many other features neglected. Those should be highlighted. Similarly, spin-phonon coupling that could be responsible for several mechanisms of light induced magnetism is not included.
5. It should be explained what kind of relaxation pathways are included here – there are many options, and which are not.
6. Fig. 3 currently doesn’t contribute a whole lot to the text. It might be better to find a more quantitative way to plot the data from the GL model, especially, to compare it directly to the model spin simulations.
7. The long timescale periodic spin dynamics (e.g. in fig 4) seem reminiscent of some magnonic excitation, perhaps also a superposition of magnons. Is that the case? It’s worth discussing.
8. The main idea presented by this paper as I see it is that in order to induce strong control over magnetization, one needs to find a material where laser-L coupling is strong – it’s worth discussing what good options might be.
Recommendation
Publish (easily meets expectations and criteria for this Journal; among top 50%)