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arXiv:2510.26288 · Physical review. B./Physical review. B

Laser-induced commensurate-incommensurate transition of charge order in a Hubbard superlattice

Hua Chai, Zhenyu Cheng, Qinxin Hu, Zhongbing Huang, Xiang Hu, Xuedong Tian, Liang Du

Published Mar 20, 2026• 0 citations
arXivHTMLPDF

Abstract

We investigate the nonequilibrium dynamics of charge density waves in a pumped one-dimensional Hubbard superlattice with staggered onsite Coulomb interactions at half-filling, using time-dependent exact diagonalization. In equilibrium, the system exhibits commensurate charge correlations consistent with the superlattice periodicity. Under laser excitation, the charge correlation function exhibits distinct behaviors across four representative frequencies, spanning both linear and nonlinear optical regimes. Notably, we observe a laser-induced commensurate-to-incommensurate transition in the charge order, manifested by a shift in the peak wavevector of the charge structure factor. This transition is driven by sublattice-selective doublon-holon dynamics, where the laser frequency and intensity determine whether excitations predominantly destabilize the charge order on the weakly or strongly interacting sublattice. Our analysis of the excitation spectrum and site-resolved correlation dynamics reveals the underlying mechanisms of this transition. These results suggest a promising optical strategy for controlling charge order in superlattice-based quantum materials.

DOI
10.1103/32y1-cy4w

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We investigate the nonequilibrium dynamics of charge density waves in a pumped one-dimensional Hubbard superlattice with staggered onsite Coulomb interactions at half-filling, using time-dependent exact diagonalization. In equilibrium, the system exhibits commensurate charge correlations consistent with the superlattice periodicity. Under laser excitation, the charge correlation function exhibits distinct behaviors across four representative frequencies, spanning both linear and nonlinear optical regimes. Notably, we observe a laser-induced commensurate-to-incommensurate transition in the charge order, manifested by a shift in the peak wavevector of the charge structure factor. This transition is driven by sublattice-selective doublon-holon dynamics, where the laser frequency and intensity determine whether excitations predominantly destabilize the charge order on the weakly or strongly interacting sublattice. Our analysis of the excitation spectrum and site-resolved correlation dynamics reveals the underlying mechanisms of this transition. These results suggest a promising optical strategy for controlling charge order in superlattice-based quantum materials.
Doublon-holon dynamics is investigated in a pumped one-dimensional Hubbard model with a staggered on-site Coulomb interaction at half-filling. When the system parameters are set to be in the Mott-insulating regime the equilibrium sublattice density of states exhibits several characteristic peaks, corresponding to the lower and upper Hubbard bands as well as hybridization bands. We study the linear absorption spectrum and find two main peaks characterizing the photon frequencies which excite the ground state to an excited state. For a system driven by a laser pulse with general intensity and frequency, both the energy absorption and the doublon-holon dynamics exhibit distinct behaviors as a function of laser amplitude and frequency. Single-photon processes are observed at low laser intensity where the energy is absorbed for resonant laser frequencies. For strong laser intensity multiphoton-induced dynamics are observed in the system that are confirmed by an evaluation of the Loschmidt amplitude. The contribution of multiphoton processes to site-resolved double occupancy is also characterized by the generalized Loschmidt amplitude. The site-resolved doublon-holon dynamics are observed in both the one and multiphoton processes and the site-resolved behavior is explained within a quasiparticle picture. Our study suggests strategies to optically engineer the doublon-holon dynamics in one-dimensional strongly correlated many-body systems.
The charge structure factor of the half-filled Hubbard superlattices with one on-site repulsive site and [Formula: see text] free sites per unit cell is investigated numerically. The behaviors of charge structure reveal a kind of even–odd [Formula: see text] disparity. For even [Formula: see text], we always observe a commensurate charge density wave (CDW). For odd [Formula: see text], we observe a commensurate–incommensurate CDW transition at a critical on-site repulsion around the particle–hole symmetric point. This transition results from the competition between the local charge correlations with odd distance and even distance.
We study the phase diagram of a half-filled one-dimensional superlattice Hubbard model with an alternating orbital energy ± ϵ/2 and on-site Coulomb repulsion U(A) and U(B) using the density-matrix renormalization group and finite-size scaling analysis. For U(A) >> U(B), we observe an incommensurate charge correlation phase. For U(B) = 0, we find a transition from the band insulating phase to the correlated metallic phase at the critical point ϵ = U(A)/2. For U(B) > 0, we find three insulating phases as in the ionic Hubbard model. In the gapless region, the correlation functions exhibit the asymptotic behavior of power-law decay as in the Tomonaga-Luttinger liquid.
Using the time-dependent Lanczos method, we study the nonequilibrium dynamics of the half-filled one-dimensional ionic Hubbard model, deep within the Mott insulating regime, under the influence of a transient laser pulse. In equilibrium, increasing the staggered potential in the Mott regime reduces the Mott gap and broadens the Hubbard bands, creating favorable conditions for impact ionization. After laser excitation, impact ionization is observed, with its occurrence depending on both the staggered potential and the laser pump frequency. By analyzing the time evolution of the kinetic, ionic, and Coulomb interaction energies, we identify a novel mechanism for impact ionization, in which excess ionic potential energy is converted into additional double occupancy-distinct from the conventional mechanism where excess kinetic energy drives this process. We further reveal that impact ionization arises from interference between excited states driven by photon excitations of the same order. These results present a new pathway for realizing impact ionization in strongly correlated electron systems.
Utilizing the exact diagonalization method, we investigate the one-dimensional Peierls-Hubbard model at quarter filling, where it manifests as an antiferromagnetic Mott insulator in units of dimers. By increasing the on-site Coulomb repulsion UUU, we observe a significant suppression of the Drude peak, based on a nonequilibrium linear-response theory capable of capturing the zero-frequency (Drude) weight of the optical conductivity under periodic boundary conditions. However, after the ultrafast photoirradiation of this model with large UUU, we detect a distinct enhancement of the Drude peak, signifying the onset of a photoinduced insulator-metal transition. Comparing these dynamics with the half-filled Hubbard model and a noninteracting spinless half-filled Su-Schrieffer-Heeger model (corresponding to the quarter-filled Peierls-Hubbard model with infinite UUU), we propose a mechanism for the photoinduced metallic state: The empty-occupied and double-occupied dimers serve as the photoinduced charge carriers, akin to the holons and doublons in the Hubbard model.
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 UUU 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 (Δ_{\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-Δ_{\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.