Magnetic field expulsion in optically driven YBa$_2$Cu$_3$O$_{6.48}$

TL;DR

This study demonstrates that optically driven YBa₂Cu₃O₆.48 exhibits magnetic field expulsion similar to superconductivity, indicating transient diamagnetism and enhanced superconducting correlations in a pseudogap phase.

Contribution

It provides direct evidence of Meissner-like diamagnetism in a photo-induced transient state of a high-Tc cuprate, linking optical properties to macroscopic superconducting behavior.

Findings

Enhanced magnetic field expulsion at sample edges under optical drive.

Measured susceptibility comparable to equilibrium type II superconductor.

Photo-induced effects are inconsistent with increased mobility alone.

Abstract

Coherent optical driving in quantum solids is emerging as a new research frontier, with many demonstrations of exotic non-equilibrium quantum phases. These are based on engineered band structures, and on stimulated nonlinear interactions between driven modes. Enhanced functionalities like ferroelectricity, magnetism and superconductivity have been reported in these non-equilibrium settings. In high-Tc cuprates, coherent driving of certain phonon modes induces a transient state with superconducting-like optical properties, observed far above T$_c$ and throughout the pseudogap phase. Questions remain not only on the microscopic nature of this phenomenon, but also on the macroscopic properties of these transient states, beyond the documented optical conductivities. Crucially, it is not clear if driven cuprates exhibit Meissner-like diamagnetism. Here, the time-dependent magnetic-field amplitude surrounding a driven YBa$_2$Cu$_3$O$_{6.48}$ sample is probed by measuring Faraday rotation in a GaP layer adjacent to the superconductor. For the same driving conditions that result in superconducting-like optical properties, an enhancement of magnetic field at the edge of the sample is detected, indicative of induced diamagnetism. The dynamical field expulsion measured after pumping is comparable in size to the one expected in an equilibrium type II superconductor of similar shape and size with a volume susceptibility $\chi_v$ of order -0.3. Crucially, this value is incompatible with a photo-induced increase in mobility without superconductivity. Rather, it underscores the notion of a pseudogap phase in which incipient superconducting correlations are enhanced or synchronized by the optical drive.