Quantum transient magnetism in YBCO seen up to 400 Kelvin

A 20 terahertz laser pulse applied to YBCO above its superconducting temperature triggers a surprising effect: the emergence of magnetism resembling superconductivity lasting just picoseconds. Researchers detected a transient magnetic field of approximately 10 microtesla for an applied field of 10 millitesla at 100 Kelvin, indicating a temporary Meissner-like effect, a hallmark of superconductivity, induced by the light. This behavior extends beyond room temperature, observed up to 300-400 Kelvin, a temperature range previously thought to preclude such magnetic responses, and suggests a pathway to controlling material states with light even where they wouldn’t normally exist.

THz Pumping Reveals Transient Phenomena in YBCO

The ability to induce magnetism in yttrium barium copper oxide, or YBCO, at temperatures exceeding 300 Kelvin has been demonstrated in experiments with a 20 terahertz laser pulse, a frequency within the mid-infrared spectrum and well above the material’s superconducting transition temperature. The study details how the applied pulse triggers a response mimicking superconductivity, but lasting only a few picoseconds.

This observation is significant because it indicates a Meissner-like effect, the expulsion of magnetic fields characteristic of superconductors, is being temporarily induced by the laser pulse. The research team proposes this effect arises from diamagnetic current loops generated within the YBCO structure, enhancing the magnetic field outside the illuminated area.

This model contrasts with interpretations relying on long-range coherence, instead focusing on short-range superconducting correlations already present within the material. The researchers attribute this phenomenon to a novel mechanism where the time-averaged dynamics of the relative phase between superconducting layers exhibit exponential growth.

“The key experimental signatures—out-of-plane optical response and second harmonic generation due to Josephson plasmons —also involve current flow perpendicular to the planes,” the paper explains, motivating the search for an explanation that doesn’t rely on net in-plane supercurrent flow. The model centers on the behavior of the relative phase θ, which describes the Josephson current between two superconductorlike layers driven by the intense laser pulse.

The researchers found that θ oscillates with a large amplitude exceeding pi, placing the system in a highly nonlinear regime. This instability leads to the injection of topological defects from the edges of the sample, effectively creating a state similar to the Pokrovsky-Talapov phase transition, but at magnetic fields significantly lower than typically required.

“One of the main achievements of this paper is the discovery of this new instability mechanism, which we term flux-Floquet instability,” the study states, emphasizing its potential universality across various systems with U(1) symmetry. The experimental setup involved pumping a YBCO multilayer segment with a pulse propagating along the y axis, with the electric field polarized along the z axis, over a spot size of about 100 micrometers in diameter, in the presence of an external static magnetic field oriented along the y axis.

The analysis shows that the onset of the flux-Floquet instability can account for the experimental data both qualitatively and quantitatively, predicting a giant paramagnetic response that can be orders of magnitude larger than the equilibrium diamagnetic response. This work, the researchers suggest, provides a microscopic theory that reproduces experimental data and offers insights into the nature of the pseudogap phase in high-temperature cuprate superconductors.

Ultrafast Control Unlocks YBCO’s Pseudogap Phase

The cuprate YBCO exhibits surprising magnetic behavior when illuminated with a 20 terahertz laser pulse, even at temperatures exceeding 300 Kelvin. The researchers propose a mechanism termed the flux-Floquet instability to explain these observations. This instability arises from the interplay between diamagnetic screening currents at the edges of the YBCO bilayers and Josephson nonlinear dynamics originating from short-range superconducting coherence.

This work extends beyond YBCO, suggesting potential universality across a range of systems exhibiting U(1) symmetry, including excitonic condensates in 2D heterostructures, extended Josephson junctions, and ultracold atomic experiments utilizing artificial gauge fields. The researchers believe this provides a new understanding of the complex interplay between light, magnetism, and superconductivity in this material.

Driven YBCO Exhibits Magnetic Field-Scaling Response

Researchers are meticulously examining the unusual magnetic response of YBCO, a high-temperature superconductor, when subjected to intense pulses of terahertz light. This behavior, previously unobserved in materials above their superconducting state, suggests a temporary induction of magnetism mimicking the Meissner effect, a hallmark of superconductivity, through non-equilibrium processes. The observed magnetic response isn’t a simple surface effect; the induced field penetrates the entire YBCO sample at the speed of light, indicating a bulk phenomenon driven by the terahertz pulse.

These edge currents, generated by the light pulse, are not merely a consequence of induced superconductivity but a distinct instability within the material’s electronic structure. Researchers detected transient magnetic field magnitudes of approximately 10 microtesla for an applied field of 10 millitesla at 100 Kelvin.

The implications of this work extend beyond understanding the pseudogap phase in high-temperature superconductors; the discovery of the flux-Floquet instability represents a novel mechanism for controlling material states with light. The microscopic theory presented not only reproduces the experimental data but also offers insights into the fundamental physics governing the pseudogap phase, potentially unlocking new avenues for materials design and quantum technologies.

YBCO Bilayer Dynamics and Josephson Current Generation

The surprising emergence of magnetism in YBCO above its superconducting temperature, extending to 400 Kelvin, stems from a dynamic interplay within the material’s layered structure. Recent work details how a 20 terahertz laser pulse induces transient effects mimicking superconductivity, even in the pseudogap phase where such behavior is not normally expected.

The observation of this magnetism at temperatures far exceeding conventional superconductivity, up to 300-400 Kelvin, challenges established understanding of the pseudogap phase in high-temperature superconductors. Analysis centers on a newly proposed mechanism termed the flux-Floquet instability, arising from the interaction between light and the material’s bilayer structure.

Driven Sine-Gordon Model Explains YBCO Behavior

The observed transient field’s magnitude is approximately 10 microtesla for an applied field of 10 millitesla at 100 Kelvin, and isn’t a result of bulk superconductivity but rather a consequence of these edge currents and their interaction with the applied magnetic field. The researchers coupled the sine-Gordon equation to Maxwell’s equations to fully capture the electromagnetic dynamics within the driven YBCO experiments. The analysis assumes the existence of short-range superconducting correlations even above the critical temperature, allowing for the definition of a local pair phase.

Maxwell’s Equations Couple to YBCO’s Electromagnetic Field

The detection of a transient magnetic field scaling with applied field confirms a surprising Meissner-like effect in YBCO even above its superconducting temperature, a phenomenon previously considered impossible. Recent work details how this temporary magnetism arises not from bulk superconductivity, but from instabilities within the material’s layered structure when exposed to intense terahertz radiation. These currents, flowing opposite to equilibrium screening currents, generate a giant paramagnetic magnetization aligned with the applied field, which can be orders of magnitude larger than the equilibrium diamagnetic response.

These currents, flowing between the YBCO bilayers, create a magnetic flux that permeates the entire segment of the material at the speed of light. The researchers suggest that this dynamical solitonic transition represents an important phenomenon in its own right, potentially unlocking new avenues for controlling material properties with light.

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