Impurities in material negatively affect superconductors

Good news! The cleaner, the better! Spooked by impurities!

"... used electron microscopy to directly verify that trace amounts of oxygen in the samples were indeed causing the spurious charge-order signal. ... 

Not only has the team identified a crucial difference between cuprate and nickelate superconductors; they now have a more reliable method for growing cleaner samples that can potentially be used for a wider variety of experiments, with a little less mystery. ..."

From the abstract:

"A hallmark of many unconventional superconductors is the presence of many-body interactions that give rise to broken-symmetry states intertwined with superconductivity. Recent resonant soft X-ray scattering experiments report commensurate 3a0 charge density wave order in infinite-layer nickelates, which has important implications regarding the universal interplay between charge order and superconductivity in both cuprates and nickelates. Here we present X-ray scattering and spectroscopy measurements on a series of NdNiO2+x samples, which reveal that the signatures of charge density wave order are absent in fully reduced, single-phase NdNiO2. The 3a0 superlattice peak instead originates from a partially reduced impurity phase where excess apical oxygens form ordered rows with three-unit-cell periodicity. The absence of any observable charge density wave order in NdNiO2 highlights a crucial difference between the phase diagrams of cuprate and nickelate superconductors."

‘Flawed’ material resolves superconductor conundrum | Cornell Chronicle

Absence of 3a0 charge density wave order in the infinite-layer nickelate NdNiO2

Fig. 4: Outline of the multistage reduction process of nickelate films and high-resolution STEM images of a partially reduced film showing 3a0 ordering.