Thermalization Fronts in the Hubbard-Holstein Model
Pith reviewed 2026-05-10 15:13 UTC · model grok-4.3
The pith
Thermalization spreads coherently in the Hubbard-Holstein model with fronts propagating at identical velocities in electrons and phonons.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Thermalization is marked by a sharp propagating front in the plane of real time and DMFT iteration number. This front appears in electronic observables already for weak quenches within the simulated time window, whereas the phononic sector exhibits a visible front only at sufficiently strong coupling. Thus, at weak coupling the local dispersionless phonons show a delayed onset of front formation, while near and beyond the crossover the front develops on comparable timescales in both the electronic and phononic sectors. Whenever both fronts are resolved, they propagate with the same velocity, showing that thermalization spreads coherently through the coupled electron-phonon system.
What carries the argument
The Step-by-Step DMFT framework, which tracks dynamics in the real-time versus iteration-number plane to expose sharp propagating fronts that mark the microscopic onset of the thermal state.
Load-bearing premise
The self-consistent Migdal approximation together with second-order perturbation theory for the electron-electron interaction remains accurate enough to capture the microscopic buildup of the thermal state across the simulated quench strengths.
What would settle it
A calculation or experiment in which the resolved electronic and phononic thermalization fronts propagate at different velocities would falsify the claim of coherent spreading.
Figures
read the original abstract
We investigate the nonequilibrium dynamics of the weak-coupling Hubbard-Holstein model after a sudden switch-on of the electron-phonon interaction within nonequilibrium dynamical mean-field theory (DMFT). Using the self-consistent Migdal approximation for the electron-phonon coupling together with second-order perturbation theory for the electron-electron interaction, we show that the relaxation dynamics exhibits a crossover between electron-dominated and phonon-dominated regimes, extending to finite Hubbard interaction the scenario previously identified in the Holstein model. To investigate the microscopic buildup of the thermal state, we analyze the dynamics within the Step-by-Step DMFT framework. In the plane of real time and DMFT iteration number, thermalization is marked by a sharp propagating front. This front appears in electronic observables already for weak quenches within the simulated time window, whereas the phononic sector exhibits a visible front only at sufficiently strong coupling. Thus, at weak coupling the local dispersionless phonons show a delayed onset of front formation, while near and beyond the crossover the front develops on comparable timescales in both the electronic and phononic sectors. Whenever both fronts are resolved, they propagate with the same velocity, showing that thermalization spreads coherently through the coupled electron-phonon system.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript investigates the nonequilibrium dynamics of the weak-coupling Hubbard-Holstein model after a sudden switch-on of the electron-phonon interaction within nonequilibrium dynamical mean-field theory (DMFT). Using the self-consistent Migdal approximation for the electron-phonon coupling together with second-order perturbation theory for the electron-electron interaction, the authors show that the relaxation dynamics exhibits a crossover between electron-dominated and phonon-dominated regimes, extending prior Holstein-model results. They analyze the microscopic buildup of the thermal state using the Step-by-Step DMFT framework, identifying sharp propagating fronts in the real-time versus DMFT-iteration plane. Electronic fronts appear for weak quenches, while phononic fronts require stronger coupling; when both are resolved, the fronts propagate at identical velocities, indicating coherent thermalization spread through the coupled system.
Significance. If the numerical results hold under the stated approximations, this work meaningfully extends the Holstein-model scenario to finite Hubbard U, offering a microscopic view of how thermalization propagates coherently in coupled electron-phonon systems. The Step-by-Step DMFT diagnostic, which treats DMFT iteration number as a spatial-like coordinate, provides a clear, parameter-free visualization of front formation and velocity equality. Direct observation of matched velocities in electronic and phononic sectors strengthens the central claim of coherent spread.
minor comments (2)
- The abstract refers to 'the simulated time window' and 'sufficiently strong coupling' without quoting specific numerical ranges for U, electron-phonon coupling strength, or quench amplitudes; adding these values would allow readers to assess the extent of the reported crossover and the regimes where both fronts are resolved.
- The Step-by-Step DMFT framework is introduced without a brief definition or citation on first use; a short explanatory sentence or reference would improve accessibility for readers outside the immediate subfield.
Simulated Author's Rebuttal
We thank the referee for the positive assessment of our manuscript and the recommendation for minor revision. The provided summary accurately captures our investigation of nonequilibrium dynamics in the Hubbard-Holstein model, the crossover between electron- and phonon-dominated regimes, and the identification of propagating thermalization fronts via the Step-by-Step DMFT framework.
Circularity Check
No significant circularity
full rationale
The paper's central results follow from direct numerical solution of the nonequilibrium DMFT equations under the self-consistent Migdal approximation for electron-phonon coupling and second-order perturbation theory for electron-electron interactions, within the Step-by-Step DMFT framework. The propagating thermalization fronts and their equal velocities (when both are resolved) are reported as observations from the simulated dynamics in the real-time vs. DMFT-iteration plane, extending prior Holstein-model behavior to finite Hubbard U without any self-referential definitions, fitted parameters renamed as predictions, or load-bearing self-citations that reduce the claim to its inputs. The derivation chain remains self-contained against the stated approximations and numerical outputs.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption The self-consistent Migdal approximation accurately describes the electron-phonon interaction in the weak-coupling regime.
- domain assumption Second-order perturbation theory is sufficient for the electron-electron interaction.
Forward citations
Cited by 1 Pith paper
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Proof of the absence of local conserved quantities in the Holstein model
The one-dimensional Holstein model and Holstein-Hubbard model have no nontrivial local conserved quantities other than the Hamiltonian and total fermion number.
Reference graph
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Step-by-Step DMFT atU= 0 For completeness, we briefly discuss the corresponding Step-by-Step DMFT results in the Holstein limitU/v ∗ = 0, shown in Figs. 7 and 8. We keep the same parameters as in the main text, namely half filling,ω 0 = 0.7, and initial inverse temperatureβ i = 100. Figure 7 shows the representative caseg f = 0.5. Pan- els (a) and (b) con...
discussion (0)
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