Redistribution of phase fluctuations in a periodically driven cuprate superconductor

TL;DR

This paper investigates how periodic optical-frequency driving suppresses phase fluctuations in a bi-layer cuprate superconductor, providing insights into light-enhanced coherence phenomena observed experimentally.

Contribution

It introduces a theoretical framework using Langevin and Fokker-Planck equations to explain how external driving reduces phase fluctuations in layered cuprates, linking to recent experimental findings.

Findings

Suppression of low-energy plasmon phase fluctuations due to external driving

Resonance amplification of high-energy plasmon effects

Reduced in-plane fluctuations on long length scales

Abstract

We study the thermally fluctuating state of a bi-layer cuprate superconductor under the periodic action of a staggered field oscillating at optical frequencies. This analysis distills essential elements of the recently discovered phenomenon of light enhanced coherence in YBa$_2$Cu$_3$O$_{6+x}$, which was achieved by periodically driving infrared active apical oxygen distortions. The effect of a staggered periodic perturbation is studied using a Langevin and Fokker-Planck description of driven, coupled Josephson junctions, which represent two neighboring pairs of layers and their two plasmons. In a toy model including only two junctions, we demonstrate that the external driving leads to a suppression of phase fluctuations of the low-energy plasmon, an effect which is amplified via the resonance of the high energy plasmon. When extending the modeling to the full layers, we find that this reduction becomes far more pronounced, with a striking suppression of the low-energy fluctuations, as visible in the power spectrum. We also find that this effect acts onto the in-plane fluctuations, which are reduced on long length scales. All these findings provide a physical framework to describe light control in cuprates.