Anomalous thermoelectric and thermal Hall effects in irradiated altermagnets

arXiv:2602.05745 · cond-mat.mes-hall · Submitted 2026-02-05 · Read on arXiv

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Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: Today's paper: "Anomalous thermoelectric and thermal Hall effects in irradiated altermagnets".

Mira: We show that a d-wave altermagnet can be transformed into a Chern insulator by irradiating it with elliptically polarized light from a high-frequency photon beam.

Kai: First, who's behind it and why it matters.

Title and authors: Kai: So we're starting with the paper "Anomalous thermoelectric and thermal Hall effects in irradiated altermagnets," and it really boils down to how shining elliptically polarized light on a d-wave altermagnet creates finite gaps at both the M and points in momentum space. This is the initial structural change they're proposing.

Mira: That gap opening is exactly what generates that nonzero Berry curvature in momentum space, which then leads directly to those intrinsic anomalous thermoelectric and thermal Hall currents whenever there's a temperature gradient present.

Lev: I find it interesting that they focus on intrinsic contributions, meaning they aren't relying on external relaxation times for these effects, which makes the topological signature more fundamental and less dependent on specific material disorder.

Kai: They go further by showing that at extremely low temperatures, the thermoelectric Hall coefficient exhibits a linear temperature dependence but then vanishes inside the bulk energy gap between the conduction and valence bands near the M point.

Mira: That vanishing inside the gap is key because it suggests that because of topology, these transport properties are fundamentally tied to those gapped regions rather than just being some trivial scattering effect occurring within the material.

Lev: So if we're thinking about building a device, this tells us that we need to design materials where that specific band structure around the M point is accessible and stable under the driving conditions for this effect to be meaningful.

Kai: They also highlight that the low-temperature thermal Hall coefficient becomes quantized across the entire bandwidth, which they say reflects the underlying topological character of this light-induced Chern insulating phase.

Mira: That quantization of thermal transport is a very strong indicator because it shows we've successfully induced a state with a definite topological character just by irradiating it.

Lev: For error correction purposes, having that quantized thermal response is something we can use as a reliable metric to confirm if our physical implementation has achieved the desired topological regime.

The paper's summary: Kai: The authors propose that the main improvement they introduce is their detailed analysis of how the critical light amplitude determines which gap opens first at M versus. This shows a more nuanced picture than just saying gaps open generally.

Mira: Specifically, they pinpoint a critical value of light amplitude where there's a transition: the gap at stays open, but it closes near M, and then reopens beyond that point.

Lev: That precise phase transition point is what we need to target for experimental realization; it gives us a clear parameter space to navigate for observing the topological change reliably.

Kai: It’s like having a precise switch; once you hit that critical amplitude, the entire system's topological character flips in a predictable way based on how strong the light is.

Mira: That transition point is also where they show the band inversion actually happens near the M point, which solidifies their claim that this isn't just a trivial band shift but a true topological phase change.

Lev: From an error correction view, having a clearly defined critical threshold helps us determine if our physical implementation can reliably operate in the desired topological regime or if we're stuck in the wrong phase.

Kai: So, they’re giving us a clear recipe for tuning the light to achieve that specific topological state they want to study by controlling that amplitude.

Mira: We should also keep an eye on the work they cite concerning g- and i-wave altermagnets, as that expands the scope of these topological realizations beyond just d-wave systems.

Lev: I think we need to focus on developing methods to probe those predicted effects using thermal Hall quantization as a primary metric for validation across different material classes.

The paper's improvements: Kai: To wrap up, the paper "Anomalous thermoelectric and thermal Hall effects in irradiated altermagnets" really establishes that thermoelectric and thermal Hall transports are powerful signatures of topology in driven altermagnetic systems. They show how light irradiation transforms a d-wave altermagnet into a Chern insulator, and the resulting quantized thermal Hall transport is a very strong physical confirmation of this idea.

Mira: I think the most important thing to remember is that this work moves these ideas from just theoretical prediction to showing how they can be realized through specific experimental tuning of the light's amplitude.

Lev: For real hardware, this means we have concrete predictions about what kind of robust topological states we can aim for when engineering these systems with external drives, which is a huge step forward in the practical side.

Kai: It’s exciting because it moves these ideas from just theoretical prediction to showing how they can be realized through specific experimental tuning of the light's amplitude, and that’s what we need to pursue experimentally.

Mira: We should also keep an eye on the work they cite concerning g- and i-wave altermagnets, as that expands the scope of these topological realizations beyond just d-wave systems.

Lev: I think we need to focus on developing methods to probe those predicted effects using thermal Hall quantization as a primary metric for validation across different material classes.

Kai: So that’s our summary of this paper, "Anomalous thermoelectric and thermal Hall effects in irradiated altermagnets," and it shows the incredible potential for light-driven topological engineering.

Mira: It really does confirm that these intrinsic transport properties are robust indicators of topology when driven by external fields like light.

Lev: I’m just looking forward to seeing how this translates into tangible, controllable experimental setups in the near future.

Conclusion: Kai: So we've covered how the paper "Anomalous thermoelectric and thermal Hall effects in irradiated altermagnets" shows that light can create Chern insulators from d-wave altermagnets, and they are really highlighting those quantized thermal effects as a way to confirm it.

Mira: I think the core idea is that these intrinsic transport properties aren't just noise; they're direct consequences of the induced topology in response to an energy gradient.

Lev: And from my perspective on error correction, seeing a clear topological signature like this under driving conditions means we have a more concrete target for designing hardware where those protected states might actually be realized.

Kai: Exactly, Lev; it’s moving us toward knowing exactly what kind of robust topological states we can aim for when engineering these systems with external drives.

Mira: We should also keep an eye on the work they cite concerning the g- and i-wave altermagnets because that expands the scope of these topological realizations beyond just d-wave systems.

Lev: I think we need to focus on developing methods to probe those predicted effects using thermal Hall quantization as a primary metric for validation across different material classes.

Kai: That's what this paper does, summarizing how light drives a d-wave altermagnet into a Chern insulator and confirms it with quantized transport measurements.

Mira: It really does confirm that these intrinsic transport properties are direct consequences of the induced topology in response to an energy gradient.

Lev: For real hardware, seeing a clear topological signature like this under driving conditions means we have a more concrete target for designing hardware where those protected states might actually be realized.

Fang Qin, *, *Xiao-Bin Qiang

School of Science, Jiangsu University of Science and Technology · State Key Laboratory of Quantum Functional Materials, Department of Physics, and Guangdong Basic Research Center of Excellence for Quantum Science, Southern University of Science and Technology (SUSTech) · Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University

cond-mat.mes-hall

Submitted: 2026-02-05

Updated: 2026-09-25

Comments: 13 pages, 4 figures, updated references, published version

Journal ref: Phys. Rev. B 114, 185427 (2026)

DOI: 10.1103/dqs3-935d

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 78/100

The gist: We show that a d-wave altermagnet can be transformed into a Chern insulator by irradiating it with elliptically polarized light from a high-frequency photon beam.

Key concepts

Chern insulator
A material state created by irradiation that has a definite topological character. This is achieved when elliptically polarized light acts on a d-wave altermagnet, causing gaps to open in momentum space, which leads to the Chern insulating phase.
Anomalous thermoelectric and thermal Hall effects
These are transport properties—thermoelectric and thermal Hall currents—that arise from the induced topology. They are intrinsic consequences of the material's gapped structure when a temperature gradient is present, not just simple scattering.
Critical light amplitude
A specific value of light intensity that determines which gap opens first at the M point in momentum space. This critical point marks a phase transition where the system's topological character flips predictably based on the light's strength.

Terminology

Summary

We show that a d-wave altermagnet can be transformed into a Chern insulator by irradiating it with elliptically polarized light from a high-frequency photon beam. We further explore the intrinsic anomalous thermoelectric and thermal Hall effects in light-irradiated altermagnets. At low temperatures, the thermoelectric Hall coefficient exhibits a linear temperature dependence but vanishes within the energy gap between the conduction and valence bands near the M point. However, it displays pronounced peaks and dips at the gap boundaries near both the M and Γ points, suggesting that thermoelectric Hall conductivity is a sensitive probe for these gapped regions. Similarly, the low-temperature thermal Hall coefficient, which also shows a linear temperature dependence, becomes quantized across the bandwidth, reflecting the underlying topological character of the light-induced Chern insulating phase. These results establish thermoelectric and thermal Hall transports as powerful signatures of topology in driven altermagnetic systems.

Upon exposure to elliptically polarized light, these Dirac points acquire finite gaps through Floquet-induced symmetry breaking, generating a nonzero Berry curvature in momentum space. Consequently, intrinsic thermoelectric and thermal Hall currents are simultaneously induced under the temperature gradient. Beyond the topological phase transition, we further investigate the intrinsic anomalous thermoelectric and thermal Hall effects in the light-driven altermagnetic phase. At extremely low temperatures, the thermoelectric Hall coefficient exhibits a linear temperature dependence and vanishes inside the bulk energy gap between the conduction and valence bands. In contrast, pronounced peaks and dips emerge at the gap edges near both the M and Γ points, indicating that the thermoelectric Hall response serves as a sensitive probe of the Floquet-induced band gaps. In parallel, the low-temperature thermal Hall coefficient also displays linear temperature scaling, while the thermal Hall conductivity becomes quantized across the bandwidth. This quantization underscores the potential of thermal Hall transport as a robust probe of the system’s underlying topological character.

In summary, this work investigates how elliptically polarized light breaks Cˆ4 T̂ symmetry and induces gaps at both the Γ and M points in the spectrum of a d-wave altermagnet. The gap around the Γ point gives rise to Chern bands with Chern number C = 1/2, while the gap around the M point contributes another Chern number C = 1/2, leading to a total Chern number of C = 1. This indicates that the d-wave altermagnet can be transformed into a Chern insulator under light irradiation with a high-frequency photon beam. Particularly, there exists a critical value of the light amplitude at which a topological phase transition occurs. As the light amplitude increases to this critical point, the gap at the Γ point remains open, but the gap near the M point closes. Beyond the critical value, the gap near the M point reopens, signifying a band inversion at the critical point. At extremely low temperatures, the thermoelectric Hall coefficient, which shows a linear temperature dependence, vanishes within the gapped region (bandwidth) between the conduction and valence bands. However, it exhibits peaks and dips at the edges of the gap regions near both the M and Γ points, suggesting that thermoelectric Hall conductivity can be used to probe both the bandwidth and the gapped region around the Γ point. Similarly, the low-temperature thermal Hall coefficient, which shows a linear temperature dependence, becomes quantized in the gapped region (bandwidth) between the conduction and valence bands. This observation suggests that thermal Hall conductivity can serve as a probe for the topological properties of the system. Analogous effects are predicted in g- and i-wave altermagnets: light irradiation can open gaps at highsymmetry points and induce anisotropic spin-orbit coupling. As a result, the predicted light-driven Chern insulating states, as well as the associated anomalous thermoelectric and thermal Hall effects, can also be realized in these systems.

The intrinsic anomalous thermoelectric current density is then expressed as (see Sec. SI of the Supplemental Material [119])

te (∇r T, µ) = −

V

n,k

and the intrinsic anomalous thermal current density can be obtained as

t (∇r T, µ) =

V

n,k

where 1/Ṙν = Fν,k (∇r T, µ) × omegan,k. At extremely low temperatures T → 0, the quantity χin xy (µ) [Eq. (13)] reduces to

2π X xy

omegan k Θ(µ−εn,k), where Θ(x) is the Heaviside step function [120–123]. Applying the Sommerfeld expansion [3, 118, 124–130], the intrinsic anomalous thermoelectric and thermal Hall conductivities simplify to

in

αxy

where δ(x) is the Dirac delta function [131] and we used the relation δ(x) = dΘ(x)/dx [120].

Improvements for AI systems

Based on the provided scientific paper, here are specific ways an AI system could be improved, along with what those improvements would enable:

  1. The core improvement lies in developing a simulation engine capable of accurately modeling and predicting topological phases induced by external driving forces (Floquet engineering) in complex magnetic materials (altermagnets).

  2. The improved AI system could perform the following specific tasks:

  3. Developing a high-fidelity, machine-learning-enhanced simulator for Floquet Hamiltonians of d-wave altermagnets to predict the transition from a trivial insulator to a Chern insulator under elliptically polarized light.

  4. Simulating the spectral evolution (band gap opening/closing) and calculating the associated Chern numbers as a function of driving parameters (light amplitude, frequency, polarization angle).

  5. Predicting topological phase transitions by accurately modeling the critical light amplitudes that lead to band inversion near high-symmetry points like the M point.

  6. The AI system could be used for materials discovery and design in spintronics:

  7. Designing novel altermagnet heterostructures (like the Bi2Se3–KV2Se2O system mentioned in Section VII) optimized for specific topological responses (e.g., maximizing the Chern number or thermal Hall quantization).

  8. Identifying material compositions and structural parameters that yield robust, light-induced topological phases with minimal driving energy requirements.

  9. The AI could enable advanced characterization of electronic transport properties:

  10. Predicting the precise temperature dependence (linear scaling, peak/dip locations) of the intrinsic anomalous thermoelectric and thermal Hall coefficients based on calculated Berry curvature profiles across different regions of the Brillouin zone (e.g., near M vs. Γ points).

  11. Using these predicted transport signatures as a diagnostic tool to map out the underlying electronic band structure (identifying bandwidths versus gapped regions) in real or simulated data, allowing for non-destructive probing of topological features.

  12. The AI system could be used for fundamental condensed matter theory:

  13. Developing a predictive framework that connects the low-temperature transport coefficients (Mott relation, Wiedemann-Franz law) directly to the calculated Chern numbers and Berry curvature, allowing theorists to rapidly assess the topological robustness of a given Hamiltonian.

  14. Analyzing experimental data from measurements (like those described in Section VII) to extract quantitative information about intrinsic topological invariants (like the Chern number or thermal Hall conductivity quantization) by fitting the predicted temperature dependencies.

  15. The AI could accelerate experimental validation:

  16. Generating precise, atomistic models of heterostructures and light-matter interactions to guide experimentalists in designing optimal setups for measuring the induced effects (e.g., optimizing electrode placement for accurate Nernst/thermal Hall measurements).

Abstract

We show that a d-wave altermagnet can be transformed into a Chern insulator by irradiating it with elliptically polarized light from a high-frequency photon beam. We further explore the intrinsic anomalous thermoelectric and thermal Hall effects in light-irradiated altermagnets. At low temperatures, the thermoelectric Hall coefficient exhibits a linear temperature dependence but vanishes within the energy gap between the conduction and valence bands near the M point. However, it displays pronounced peaks and dips at the gap boundaries near both the M and Γ points, suggesting that thermoelectric Hall conductivity is a sensitive probe for these gapped regions. Similarly, the low-temperature thermal Hall coefficient, which also shows a linear temperature dependence, becomes quantized across the bandwidth, reflecting the underlying topological character of the light-induced Chern insulating phase. These results establish thermoelectric and thermal Hall transports as powerful signatures of topology in driven altermagnetic systems.

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