Photoinduced melting dynamics and collective mode in a correlated charge-order system

TL;DR

The paper investigates how a correlated charge-ordered state in a one-dimensional spinless fermion system responds to photoexcitation, focusing on the role of a collective phase mode with frequency $Ω_c ≈ Δ_{ m CO}/2$. Using time-dependent Hartree-Fock and exact diagonalization, it shows that when the pump frequency $ω_p$ is near $Ω_c$, the transient spectral function develops an in-gap weight that grows with pump strength and drives a collapse of the charge gap, whereas $ω_p > Δ_{ m CO}$ mostly induces interband excitations that shrink the gap. The comparison reveals that quantum fluctuations, captured by ED, broaden the resonance and hasten CO destabilization beyond HF predictions, with inhomogeneity further facilitating relaxation to a photoinduced metallic state. The results highlight a distinct, collective-mode–driven pathway for photoinduced melting in correlated electron systems and provide spectral fingerprints for identifying such dynamics in real materials.

Abstract

We theoretically investigate the transient spectral function during the photoinduced melting of charge order in a correlated electron system, to unravel the dynamical processes triggered by different initial excitations. We employ a one-dimensional interacting spinless fermion model introducing a pulsed laser light, and perform a comparative study by the Hartree-Fock approximation and by the exact diagonalization method to numerically solve the time-dependent Schrödinger equation. We find characteristic behavior in the transient spectral function, whose features strongly depend on the pump light frequency $ω_p$. When $ω_p$ is resonant with the collective phase mode of frequency $Ω_c\simeq Δ_{\rm CO}/2$, where $Δ_{\rm CO}$ is the charge gap, the transient spectral function exhibits a photoinduced in-gap weight which triggers large responses. With increasing the laser intensity, the development of in-gap weight directly turns into the collapse of the gap. This charge-order destabilization process is in sharp contrast to the case of $ω_p>Δ_{\rm CO}$, where the photoirradiation induces interband electron-hole excitations giving rise to a shrinkage of the gap. The impact of quantum fluctuations and spatial inhomogeneity on the photoinduced dynamics is also discussed.

Figures (9)

• Figure 1: (a) Linear optical absorption spectrum $\alpha(\omega)$. Time evolution of $\phi$ under pulsed laser light with (b) $\omega_p=2.11$ and (c) $\omega_p=6.0$ for $\tau_p=3$. The shaded region indicates the time domain where the pump light is applied. The arrows mark the probe time $\tau=\tau_{\rm pr}$ of the transient spectral functions. We use $V=3$ and $N=400$.
• Figure 2: Photoemission spectra $A^<_k(\varepsilon,\tau_{\rm pr})$ for (a) $A_p=0.6$, (b) $1.0$, and (c) $2.4$ with $\omega_p=2.11$. (d) $A^<_k(\varepsilon,\tau_{\rm pr})$ for $A_p=6.0$ with $\omega_p=6.0$. The green dashed curves indicate the HF bands of the CO ground state. In (c), the red dashed curves show the HF metallic bands with $\phi=0$.
• Figure 3: Momentum integrated DOS (a) $D^<(\varepsilon,\tau_{\rm pr})$ and (b) $D(\varepsilon,\tau_{\rm pr})$ for different values of $A_p$ with $\omega_p=2.11$. (c) $D^<(\varepsilon,\tau_{\rm pr})$ and (d) $D(\varepsilon,\tau_{\rm pr})$ with $\omega_p=6.0$. We use $\tau_{\rm pr}=10$.
• Figure 4: Electron densities $\langle n_i\rangle$ near the impurity site $i=i_p$ for (a) charge-rich and (b) charge-poor sites in the ground state with $\delta_{\rm imp}=-0.1$. (c) Time evolutions of $\phi$ with $\delta_{\rm imp}=0$ and $-0.1$. $D(\varepsilon,\tau_{\rm pr})$ for different values of $\tau_{\rm pr}$ with (d) $\delta_{\rm imp}=0$ and (e) $\delta_{\rm imp}=-0.1$. In (c)-(e), we use $\omega_p=2.11$, $\tau_p=3$, and $A_p=2.4$.
• Figure 5: (a) Linear optical absorption spectra $\alpha(\omega)$ for $N=18$ and $22$. Time evolution of $\phi$ under pulsed laser light with (b) $\omega_p=1.0$ and (c) $\omega_p=5.0$ for $\tau_p=3$ and $N=22$. The shaded region indicates the time domain where the pump light is applied. The arrows mark the probe time $\tau=\tau_{\rm pr}$ of the transient spectral functions.