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arXiv:2509.06939

Ultrafast electronic coherence from slow phonons

Mattia Moroder, Sebastian Paeckel, Matteo Mitrano, John Sous

Published Sep 8, 2025• 0 citations
arXivHTMLPDF

Abstract

Light offers a route to engineer new phases of matter far from equilibrium, including transient states suggestive of superconducting, charge-ordered, and excitonic ordering behavior. Yet it remains unclear how optical excitation can dynamically produce long-range phase coherence-a defining feature of true order such as superconductivity-rather than merely enhancing local pairing. Here we show that impulsively driven low-frequency phonons enhance long-range electronic correlations in a low-dimensional metal. Through numerically exact simulations, we demonstrate that slow phonons suppress dynamical disorder, enabling buildup of coherence and enhancement of charge (and pairing) orders. These findings provide direct evidence that light can mediate enhancement of long-range order and suggest that future experimental strategies-such as the design of selective excitations of narrow phonon distributions to limit dephasing-may offer viable routes to design and stabilize transient superconducting states.

DOI
10.48550/arxiv.2509.06939

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Strong optical drives have been shown to induce transient superconducting-like response in materials above their equilibrium TcT_cTc​. Many of these materials already exhibit short-range superconducting correlations in equilibrium. This motivates the question: can external driving enhance coherence in systems with superconducting correlations but no long-range order? We explore this scenario in the two-dimensional XY model with a periodically modulated stiffness using overdamped Langevin dynamics. We find that, even though the modulation leaves the average coupling unchanged, the drive can markedly increase long-range, time-averaged correlations in systems well above the equilibrium Berezinskii-Kosterlitz-Thouless temperature. The outcome depends on the ratio of the drive frequency to the intrinsic relaxation rate: faster drives primarily heat the system, suppressing correlations and conductivity. For slower drives, the optical conductivity is modified so that the real part exhibits a prolonged effective Drude scattering time, while the imaginary part has a strengthened low-frequency 1/ω1/ω1/ω behavior. We map out these regimes across temperature, frequency, and amplitude, and rationalize them via simple analytics and vortex-thermalization arguments. Overall, we identify a generic nonequilibrium route to enhance coherence in XY-like systems, with potential relevance to experiments reporting light-induced superconductivity.
Engineering quantum phases using light is a novel route to designing functional materials, where lightinduced superconductivity is a successful example.Although this phenomenon has been realized experimentally, especially for the high-T c cuprates, the underlying mechanism remains mysterious.Using the recently developed variational non-Gaussian exact diagonalization method, we investigate a particular type of photoenhanced superconductivity by suppressing a competing charge order in a strongly correlated electron-electron and electron-phonon system.We find that the d-wave superconductivity pairing correlation can be enhanced by a pulsed laser, consistent with recent experiments based on gap characterizations.However, we also find that the pairing correlation length is heavily suppressed by the pump pulse, indicating that light-enhanced superconductivity may be of fluctuating nature.Our findings also imply a general behavior of nonequilibrium states with competing orders, beyond the description of a mean-field framework.
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