Magnetic fields can 'revive' superconductivity in nickelates, research reveals – Image for illustrative purposes only (Image credits: Unsplash)
Researchers at City University of Hong Kong led a study that upended a fundamental principle of superconductivity: strong magnetic fields can revive the phenomenon in certain nickelate materials after initially suppressing it. Published in Nature, the work centers on Eu-doped infinite-layer nickelates, where superconductivity re-emerges in extreme fields exceeding 15 tesla – roughly 300,000 times Earth’s magnetic field. This re-entrant behavior, stable across wide temperature ranges, field strengths, and orientations, marks a rare instance of magnetism bolstering rather than breaking superconductivity in materials with relatively high transition temperatures.
Superconductivity Meets Its Magnetic Foe
Superconductors conduct electricity without resistance and expel magnetic fields in what is known as the Meissner effect. Conventionally, applied magnetic fields disrupt these paired electrons, quenching superconductivity above a critical field strength. Generations of experiments reinforced this antagonism, particularly in high-temperature superconductors like cuprates.
Yet exceptions exist in niche systems, such as heavy-fermion materials, where fields sometimes induce or restore superconducting states. Infinite-layer nickelates, a newer family structurally akin to cuprates but centered on nickel, offered a fresh testing ground. A team under Professor Danfeng Li explored how rare-earth magnetism influences these properties.
Engineering the Material Breakthrough
The key material was Sm0.95-xCa0.05EuxNiO2, with europium doping tuned to an over-doped, Eu-rich regime. Professor Li’s group precisely incorporated europium during synthesis, leveraging their expertise from the 2019 discovery of superconductivity in these nickelates alongside a Stanford team. Thin films of this composition revealed unusual transport behaviors under magnetic stress.
At low fields, the initial superconducting state vanished as expected. But at higher fields, zero-resistance transport returned, confirmed alongside diamagnetic screening – a hallmark of true superconductivity. This phase persisted robustly, defying narrow angular sensitivities seen in prior re-entrant cases, which limited to just 2 to 10 degrees.
Key Observations in the Re-Entrant Phase
- Superconductivity follows a “superconducting-normal-superconducting” sequence with increasing field.
- Revival kicks in above about 15 tesla, stable from 0 to 90 degrees orientation.
- Nonlinear Hall transport and hysteretic magnetoresistance signal unconventional electron dynamics.
- Broad robustness across temperatures and fields sets it apart from fragile prior examples.
These traits emerged consistently in the targeted doping range, pointing to intrinsic material responses rather than artifacts.
Decoding the Magnetic Compensation Puzzle
A leading explanation invokes compensation: europium ions generate an internal exchange field that opposes the applied one, potentially realigning conditions for electron pairing. This mechanism partially matched data but faltered at peak doping levels, where deviations hinted at deeper interactions.
Professor Denver Li Danfeng, Associate Dean for Research and Postgraduate Education at CityUHK’s College of Science, captured the significance: “This surprising discovery demonstrates a field-induced superconducting phase in oxide superconductors with relatively high transition temperatures, analogous to those observed in heavy-fermion superconducting materials. It establishes a bridge between high-temperature superconductivity and magnetism-driven quantum phenomena.”
His statement underscores how the findings probe the delicate interplay of magnetism and pairing, challenging views of their incompatibility.
| Aspect | Conventional Superconductivity | Re-Entrant in Eu-Doped Nickelates |
|---|---|---|
| Field Effect | Suppresses above critical B | Suppresses low B, revives high B |
| Angular Stability | Narrow tolerance | 0° to 90° |
| Mechanism Role | Magnetism destructive | Magnetism partially compensatory |
Unlocking Doors to Quantum Innovation
The discovery positions nickelates as a prime platform for magnetism-enhanced superconductivity in correlated oxides. It invites scrutiny of how rare-earth magnetism tunes pairing mechanisms, potentially informing designs for robust, high-field devices like quantum sensors or efficient power lines.
While questions linger – such as exact pairing symmetries and scalability – the work bridges high-temperature superconductivity with exotic quantum states. Professor Li’s team continues pushing boundaries, building on nickelates’ promise since their debut. This revival under duress not only rewrites field effects but also fuels optimism for materials that thrive where others fail.