Spin fluctuations linked to superconductivity in electron-doped cuprate

Researchers have identified fluctuating spins as the dominant source of electrical resistance in an electron-doped copper-oxide superconductor and found that the strength of this interaction tracks the material’s critical temperature, the temperature below which it enters a superconducting state. The result provides direct experimental support for spin-fluctuation-mediated pairing in the studied cuprate, although the team stresses that it solves only part of the wider mystery of high-temperature superconductivity. The peer-reviewed study, led by physicists from the University of Bristol with international collaborators, was published in Nature Physics on 19 October 2026.

The work focuses on lanthanum cerium copper oxide, one of the materials produced by introducing additional electrons into a parent copper-oxide compound. Substitution of lanthanum with cerium is the electron-doping strategy used in the experiment. This differs from the other principal approach, in which chemical substitutions remove electrons and create mobile charge carriers called holes.

The distinction matters because the highest critical temperatures are found among hole-doped cuprates, whereas the new measurements establish the link between spin fluctuations and superconductivity on the electron-doped side. Superconductivity permits electrical current to flow without energy loss, and the researchers sought to determine which microscopic process is responsible for the transition in the electron-doped material. In conventional, lower-temperature superconductors, the relevant process involves vibrations of the ions forming the crystal lattice.

For many years, researchers have searched for a different mechanism in high-temperature copper oxides, with fluctuating electronic spin and charge considered important possibilities. Electrons possess both a charge, which can fluctuate in space and time, and a spin, which produces a magnetic field and can likewise fluctuate. The new experiment concentrates on how conduction electrons interact with these spin fluctuations.

Although spin and charge fluctuations had previously been mapped in considerable detail in copper oxides, the supplied research describes a missing connection: evidence tying the strength of the interaction between conduction electrons and those fluctuations to the critical temperature, or Tc. The central idea was that this information might be encoded in the material’s electrical resistance. If resistance could be measured across finely spaced values of Tc while other experimental variables remained controlled, the researchers could test whether the strength of the electron–spin interaction varied with the superconducting transition temperature.

To create such a range of transition temperatures within one specimen, the team prepared a special lanthanum cerium copper oxide thin film. They deposited the material layer by atomic layer on a substrate, producing a smooth gradient in Tc along the film’s length. The gradient extended from the maximum value in the sample to zero.

Because the transition temperature changed gradually across the device, the specimen supplied many closely spaced superconducting states that could be investigated using the same film. The researchers used lithography to pattern a series of electrical contacts along the film. This arrangement allowed them to measure resistance at many values of Tc while keeping the level of disorder constant across the sample.

The experiments were performed at the high magnetic-field facility of the European Magnetic Field Laboratory in the Netherlands. During magnetotransport measurements, the team recorded changes in resistance as a function of temperature, applied magnetic-field strength and local Tc. The thin-film samples were loaded into a cryostat, cooled to temperatures close to absolute zero and inserted into the bore of the magnet for these measurements.

Analysis of the high-field resistance data allowed the team to identify the dominant source of scattering in the material. The resulting interpretation was that conduction electrons scatter from fluctuating spins, and the strength of this interaction correlated with Tc. In other words, the quantity associated with the electron–spin interaction changed systematically as the point of the superconducting transition changed across the film.

The investigators regard this correlation as confirmation that the superconductivity observed in this material originates from the interaction between conduction electrons and spin fluctuations. The paper reports this result as evidence for spin-fluctuation-mediated pairing in electron-doped cuprates. The findings are significant because they connect a measurable transport property with a proposed microscopic pairing process in a material known for high-temperature superconductivity.

The specially engineered gradient film made it possible to examine the relationship over a broad range of critical temperatures without changing the underlying film, and the high-field measurements supplied the resistance data used for the analysis. The result does not establish that spin fluctuations are the only relevant process in all copper oxides. Rather, it identifies the dominant interaction and its relationship to Tc in the electron-doped compound examined here, narrowing the explanation of superconductivity for this particular part of the cuprate family.

The study nevertheless leaves a second ingredient unresolved. The researchers note that electron- and hole-doped cuprates are made from the same broad family of materials but behave differently, particularly in the values of Tc they attain. The highest Tc values occur only on the hole-doped side.

It may appear that simply increasing the strength of coupling to fluctuating spins, or increasing the frequency of those fluctuations, would extend the electron-doped result to the higher transition temperatures of hole-doped materials. Their earlier high-field studies of the hole-doped counterparts, however, indicate that this simple explanation is insufficient and that another ingredient is responsible for their higher Tc values. That limitation is central to the study’s interpretation.

The team has found what it describes as the first key ingredient in one side of the superconductivity puzzle, but says that theorists will need a complete account of both electron- and hole-doped behavior before the full mechanism of high-temperature superconductivity can be assembled. Its narrower finding is experimentally specific: in the specially prepared electron-doped film, the dominant resistance was attributed to scattering from fluctuating spins, and the strength of that interaction tracked Tc. Identifying this first component gives researchers a concrete foundation for investigating the missing factor associated with the higher transition temperatures of hole-doped cuprates.

Subject of Research: Experimental evidence for spin-fluctuation-mediated pairing in electron-doped copper-oxide superconductors

Article Title: Researchers discover ‘smoking gun’ to help solve mystery of high-temperature superconductivity

Article References: Researchers discover ‘smoking gun’ to help solve mystery of high-temperature superconductivity. Original publication (Bibliographic details unavailable.)

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Keywords: high-temperature superconductivity, electron-doped cuprates, spin fluctuations, critical temperature, magnetotransport, electrical resistance, lanthanum cerium copper oxide, thin films, Nature Physics, Researchers, discover, smoking