Dynamical decoherence of the light induced interlayer coupling in YBa$_{2}$Cu$_{3}$O$_{6+\delta}$

TL;DR

This study investigates how light-induced interlayer coupling in YBa₂Cu₃O₆+δ relaxes, revealing that transient superfluid tunneling, rather than quasiparticle transport, explains the observed plasma mode above T_c.

Contribution

It provides evidence that the relaxation of light-induced interlayer coupling occurs via coherence length collapse, supporting transient superfluid tunneling as the mechanism.

Findings

Transient plasma mode relaxes through coherence length collapse.

Quasiparticle transport does not explain the plasma mode relaxation.

Supports superfluid tunneling as the origin of light-induced interlayer coupling.

Abstract

Optical excitation of apical oxygen vibrations in YBa$_{2}$Cu$_{3}$O$_{6+\delta}$ has been shown to enhance its c-axis superconducting-phase rigidity, as evidenced by a transient blue shift of the equilibrium inter-bilayer Josephson plasma resonance. Surprisingly, a transient c-axis plasma mode could also be induced above T$_{c}$ by the same apical oxygen excitation, suggesting light activated superfluid tunneling throughout the pseudogap phase of YBa$_{2}$Cu$_{3}$O$_{6+\delta}$. However, despite the similarities between the above T$_{c}$ transient plasma mode and the equilibrium Josephson plasmon, alternative explanations involving high mobility quasiparticle transport should be considered. Here, we report an extensive study of the relaxation of the light-induced plasmon into the equilibrium incoherent phase. These new experiments allow for a critical assessment of the nature of this mode. We determine that the transient plasma relaxes through a collapse of its coherence length rather than its carrier (or superfluid) density. These observations are not easily reconciled with quasiparticle interlayer transport, and rather support transient superfluid tunneling as the origin of the light-induced interlayer coupling in YBa$_{2}$Cu$_{3}$O$_{6+\delta}$.