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arxiv: 2605.01388 · v1 · submitted 2026-05-02 · ⚛️ physics.optics

Tracking doublon-holon dynamics in high-harmonic generation from Mott insulators

Tao-Yuan Du , Hui-Ru Li , Bo Li , Ruifeng Lu This is my paper

Pith reviewed 2026-05-09 18:22 UTC · model grok-4.3

classification ⚛️ physics.optics
keywords high-harmonic generationMott insulatorsdoublon-holon dynamicsHubbard modelstrong-field physicsintraband responseinterband transitions
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The pith

Mott insulators exhibit a filling-dependent crossover in high-harmonic generation from intraband Bloch response at low density to interband doublon-holon processes near half filling.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines high-harmonic generation in a laser-driven one-dimensional Hubbard chain modeling Mott insulators. By tracking doublon population through projections onto equilibrium Hubbard bands, it separates intraband spin-wave-like currents from interband doublon-holon creation. A clear crossover appears with electron filling: dilute systems show Bloch-like intraband motion, intermediate fillings mix both channels, and near half filling the response becomes interband-dominated, producing a plateau and cutoff set by the Mott gap. Increasing interaction strength U enlarges this gap and localizes carriers, strongly suppressing interband contributions. The analysis links equilibrium spin-charge separation to nonequilibrium strong-field emission and shows how dephasing affects coherence and net doublon accumulation.

Core claim

Projecting the driven dynamics onto equilibrium Hubbard bands reveals that doublon population and its time evolution diagnose two distinct excitation channels: intraband (spin-wave-like) motion at low filling and interband doublon-holon pair creation near half filling. This produces a filling-dependent crossover in the HHG spectrum, with interband processes generating the characteristic plateau and cutoff once the system approaches half filling, while larger U suppresses interband weight through gap enlargement and correlation-induced localization.

What carries the argument

Doublon population dynamics obtained by projecting the time-dependent state onto equilibrium Hubbard bands, used as a diagnostic to decompose intraband (spin-wave-like) and interband (doublon-holon creation) current channels.

If this is right

  • At low filling the HHG response follows Bloch-like intraband oscillations without a clear cutoff.
  • Near half filling interband doublon-holon creation dominates and produces a plateau whose width tracks the Mott gap.
  • Increasing U suppresses interband contributions by enlarging the gap and localizing carriers.
  • Intra- and interband currents flow in opposite directions below the Mott gap, while dephasing selectively damps interband coherence and enhances net doublon accumulation.
  • Time-frequency analysis of the emitted light reveals distinct quantum trajectories that change with filling and appear as filling-dependent emission below the Mott gap.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same doublon diagnostic could be applied to two-dimensional or three-dimensional Hubbard models to test whether the crossover survives beyond one dimension.
  • Doping level may serve as an experimental knob to switch HHG between intraband and interband regimes in real correlated materials.
  • The opposing current flows below the gap suggest a possible route to control net charge transfer or photocurrent direction via laser parameters.

Load-bearing premise

The one-dimensional Hubbard chain treated with exact diagonalization and time-dependent density-matrix propagation captures the essential physics of real three-dimensional Mott insulators driven by strong lasers.

What would settle it

Experimental HHG spectra from doped Mott insulators that show no filling-dependent shift in plateau position or no suppression of high harmonics with increasing interaction strength.

Figures

Figures reproduced from arXiv: 2605.01388 by Bo Li, Hui-Ru Li, Ruifeng Lu, Tao-Yuan Du.

Figure 1
Figure 1. Figure 1: (c) shows the doublon number associated with each eigenstate. The distinct doublon distributions under the two filling conditions imply that the corresponding light-driven doublon dynamics lead to different harmonic radiation. In the following, we analyze the filling-dependent doublon dy￾namics and their relation to the nonlinear current and HHG spectra. Figures 2(a-c) then show the filling-dependent cur￾r… view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2 view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3 view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4 view at source ↗
read the original abstract

High-harmonic generation (HHG) in strongly correlated Mott insulators is investigated using exact diagonalization and time-dependent density-matrix propagation of a laser-driven one-dimensional Hubbard chain. By projecting onto equilibrium Hubbard bands, we use the doublon population and its dynamics as a diagnostic to analyze intraband (spin-wave-like) and interband (doublon-holon creation) excitation channels. A filling-dependent crossover emerges: Bloch-like intraband response at dilute filling, mixed dynamics at intermediate filling, and interband-dominated HHG with plateau and cutoff near half filling. In the considered parameter range, increasing interaction strength $U$ strongly suppresses interband contributions through the enlarged Mott gap and correlation-induced localization. Intra- and interband current decomposition reveals opposing flows below the Mott gap (\Delta_{\mathrm{Mott}}) and selective dephasing suppression of interband coherence, enhancing net doublon accumulation. Time-frequency analysis uncovers the filling-dependent features of quantum trajectories, manifesting in distinct below-\Delta_{\mathrm{Mott}} emission. This doublon-based analysis provides a transparent link between equilibrium spin-charge separation and nonequilibrium strong-field response, and clarifies how dephasing modifies interband coherence and doublon accumulation.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 3 minor

Summary. The manuscript investigates high-harmonic generation (HHG) in Mott insulators by simulating a laser-driven one-dimensional Hubbard chain using exact diagonalization and time-dependent density-matrix propagation. It introduces a doublon population diagnostic projected onto equilibrium Hubbard bands to distinguish intraband (spin-wave-like) and interband (doublon-holon) excitation channels. The central claims are a filling-dependent crossover in HHG response—from Bloch-like intraband at dilute fillings, through mixed dynamics, to interband-dominated with plateau and cutoff near half filling—and strong suppression of interband contributions with increasing interaction strength U due to the enlarged Mott gap and correlation-induced localization. Additional analyses include intra/interband current decomposition, dephasing effects, and time-frequency analysis linking to quantum trajectories and below-gap emission.

Significance. If the results hold, this work provides a valuable microscopic understanding of how electron correlations and filling control HHG in strongly correlated systems, offering a bridge between equilibrium spin-charge separation and nonequilibrium strong-field phenomena. The doublon-based analysis could inform experimental interpretations of HHG spectra in materials like transition metal oxides. The suppression with U highlights the role of correlations in controlling emission channels.

major comments (2)
  1. [Methods] The central claims of a filling-dependent crossover and U-induced suppression rest entirely on simulations of the 1D Hubbard chain (Methods section). The manuscript invokes 1D spin-charge separation to connect equilibrium bands to nonequilibrium doublon dynamics, but provides no quantitative discussion or test of how these features change in 2D or 3D lattices where spin-charge separation is absent; this is load-bearing for the generality asserted in the abstract.
  2. [Results] In the Results section, convergence checks with respect to chain length (number of sites) and time-step size for the time-dependent density-matrix propagation are not reported for the key observables (doublon population, intra/interband currents, and HHG spectra), particularly near half filling where finite-size effects and strong correlations are pronounced.
minor comments (3)
  1. [Abstract] The abstract refers to 'the considered parameter range' without listing explicit values of U, filling, laser frequency, or intensity; these should appear in a table or the first paragraph of the Model section for reproducibility.
  2. [Throughout] Notation for the Mott gap (denoted Δ_Mott) and related quantities is introduced without a dedicated definition paragraph; a consistent first-use definition would improve clarity.
  3. [Discussion] The time-frequency analysis of quantum trajectories is presented without reference to prior HHG trajectory literature in correlated systems; adding 1-2 citations would place the below-Δ_Mott emission features in context.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for their careful reading and constructive comments on our manuscript. We address each major comment point by point below and have revised the manuscript where appropriate to improve clarity and rigor.

read point-by-point responses

  1. Referee: [Methods] The central claims of a filling-dependent crossover and U-induced suppression rest entirely on simulations of the 1D Hubbard chain (Methods section). The manuscript invokes 1D spin-charge separation to connect equilibrium bands to nonequilibrium doublon dynamics, but provides no quantitative discussion or test of how these features change in 2D or 3D lattices where spin-charge separation is absent; this is load-bearing for the generality asserted in the abstract.

    Authors: The manuscript explicitly studies the one-dimensional Hubbard model, as stated in the abstract and Methods, where spin-charge separation is exact and enables a direct mapping from equilibrium bands to doublon-holon dynamics. We do not provide quantitative tests in 2D or 3D because exact diagonalization does not scale to those dimensions. To address the concern, we have revised the abstract to stress the one-dimensional setting and added a paragraph in the Discussion clarifying that while the Mott-gap suppression mechanism is expected to be relevant more broadly, quantitative details may differ in higher dimensions due to the absence of spin-charge separation. Extensions would require other methods such as DMFT. revision: partial

  2. Referee: [Results] In the Results section, convergence checks with respect to chain length (number of sites) and time-step size for the time-dependent density-matrix propagation are not reported for the key observables (doublon population, intra/interband currents, and HHG spectra), particularly near half filling where finite-size effects and strong correlations are pronounced.

    Authors: We agree that explicit convergence checks strengthen the results. In the revised manuscript we have added a new subsection (and corresponding Supplementary Material) reporting convergence tests for the doublon population, intra- and interband currents, and HHG spectra with respect to chain length (N = 8–16 sites) and time-step size. These confirm that the filling-dependent crossover and U-suppression features remain qualitatively robust near half filling, although quantitative finite-size corrections are larger in the strongly correlated regime. revision: yes

standing simulated objections not resolved
  • Quantitative tests or detailed discussion of how the reported crossover and suppression change in 2D or 3D lattices, as these lie outside the reach of the exact-diagonalization methods used in the present work.

Circularity Check

0 steps flagged

No significant circularity in simulation-based derivation

full rationale

The paper computes HHG spectra and doublon-holon dynamics directly via exact diagonalization plus time-dependent density-matrix propagation on the 1D Hubbard chain. The filling-dependent crossover, intra/interband decomposition, and U-suppression of interband channels are numerical outputs of these simulations, not algebraic reductions or fitted parameters renamed as predictions. The doublon diagnostic is constructed from equilibrium bands but applied to driven trajectories without self-definition or tautological closure. No load-bearing self-citations, uniqueness theorems, or ansatzes imported from prior author work appear in the provided derivation chain. The analysis remains self-contained as forward simulation results.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

Central claim rests on the standard 1D Hubbard Hamiltonian, projection onto equilibrium bands, and the validity of doublon counting as a proxy for excitation channels; no new entities postulated.

free parameters (2)
  • interaction strength U
    Varied to show suppression of interband contributions; fitted or chosen to enlarge Mott gap.
  • electron filling
    Scanned across dilute to half-filling to reveal crossover behavior.
axioms (2)
  • domain assumption The 1D Hubbard model captures essential Mott physics under laser driving.
    Invoked throughout the simulation setup and interpretation of doublon dynamics.
  • domain assumption Projection onto equilibrium Hubbard bands remains valid during strong-field driving.
    Used to define doublon population diagnostic.

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discussion (0)

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