Laser-Induced Commensurate-Incommensurate Transition of Charge Order in a Hubbard Superlattice

TL;DR

The paper investigates how ultrafast optical pulses can dynamically control the commensurability of charge order in a one-dimensional Hubbard superlattice with alternating on-site interactions. Using time-dependent exact diagonalization and a Peierls-substituted drive, it shows that laser frequency and intensity selectively generate doublon-holon excitations on specific sublattices, driving a commensurate-to-incommensurate transition as revealed by the time evolution of the charge structure factor $N(q,t)$ and site-resolved correlations. Four representative frequencies reveal a spectrum of responses: some pulses stabilize the original commensurate order, while others induce robust incommensurate states via distinct inter- and intra-sublattice dynamics, captured by a time-dependent criterion $\mathbb{F}(t)$. The results establish a viable optical route to switch charge-order commensurability in correlated superlattices, with potential implications for optically controlled quantum devices and the interplay between charge order and other collective phenomena.

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.

Figures (4)

• Figure 1: (a) Sublattice resolved density of states, where lower and upper Hubbard bands and hybridization bands are labeled, and a broadening parameter $\eta = 0.1$ is employed.(b) For fixed $U_\mathrm{A}=18.0$, correlation functions as a function of $U_\mathrm{B}$ are plotted for AA, AB, and BB lattice sites, respectively. The critical $U_\mathrm{B} \approx 2.0$ between incommensurate-commensurate electron correlation is labeled as a dashed line.
• Figure 2: Time evolution of the total energy as the studied system is driven by laser. Two represented laser intensity $A_0 = 0.1, 0.6$ are adopted, respectively. Note, a shift of ground state energy to zero is contained. (a) Single photon processes with laser frequency $\Omega = 3.2,11.4$, (b) Multi-photon processes with $\Omega = 6.0, 9.4$.
• Figure 3: Laser-induced commensurate-incommensurate transition dynamics. (a-d) Time evolution of the normalized peak wavevector $q_\mathrm{max}(t)/\pi$ of the charge structure factor for different laser frequencies. (e-h) Corresponding momentum- and time-resolved evolution of the charge structure factor $N(q,t)$. The system parameters are $L=14$, $U_\mathrm{A} = 18.0$ and $U_\mathrm{B} = 3.0$ with laser parameters: (a,e) $\Omega = 3.2, A_0 = 0.1$; (b,f) $\Omega = 11.4, A_0 = 0.1$; (c,g) $\Omega = 6.0, A_0 = 0.6$, (d) $\Omega = 9.4, A_0 = 0.6$.
• Figure 4: Time evolution of the charge correlation function $C_{AA}, C_{AB}, C_{BB}$ for Hubbard superlattices with fixed position-dependent Coulomb interaction strengths $U_\mathrm{B} = 18.0$ and $U_\mathrm{B} = 3.0$ with chain size $L=14$, where $C_{AA}, C_{AB}, C_{BB}$ represent the A-A, B-B, A-B sublattice charge correlation function. (a) The single photon process with $A_0=0.1, \Omega = 3.2$, (b) The single photon process with for $\Omega = 6.0$, (c) The double photon process with for $\Omega = 9.4$, (d) The double photon process with for $\Omega = 11.4$.