The international team has observed a surprising phenomenon in nickel oxide materials during cooling. Instead of freezing, certain fluctuations actually increase as the temperature drops. Nickel oxide is a model system structurally similar to high-temperature superconductors. Experiments once again show that the behavior of this class of material is still surprising.
In virtually every problem, low temperature It means that the microscopic components move less. The less heat energy available, the less often atoms reposition. Magnetic moment Their direction: They freeze. For the first time, an international team led by HZB and DESY scientists observed the opposite behavior of nickel oxide materials. High temperature superconductor.. This nickate fluctuation does not freeze when cooled, but is faster.
We observed them using the innovative technology of X-ray correlation spectroscopy. This allowed us to track the order of the basic magnetic moments (spins) in space-time using coherent soft X-rays. When cooled, these spins are arranged in a striped pattern. This ordering is not perfect at high temperatures, but consists of a random arrangement of locally ordered small regions. We have found that this arrangement is not static and varies on a time scale of a few minutes. As cooling continues, these fluctuations initially slow down and the individual areas of order grow. So far, this behavior corresponds to what many sources show. Thermal energy The more available, the more fluctuations will freeze and the more orders will increase.
Completely unusual and never observed in this way, as the material cooled further, the variability became faster again and the ordered area shrank. Therefore, the order of the stripes decays at low temperatures, both spatially and by fluctuating faster and faster, providing a kind of antifreeze.
This observation may help in a better understanding High temperature superconductivity In copper oxide (copper oxide).Copper oxides are thought to compete with the same striping order as nickel salts. Superconductivity.. Again, low temperatures attenuate the stripe order. This is described as superconductivity, and when set at low temperatures, stripe order is suppressed. Although nickates do not have superconductivity, the stripe order still decays at low temperatures, so it seems that an important aspect is missing from the current description of cuprate superconductivity. Not only is the copper oxide streaks simply suppressed, but they can collapse for essential reasons and “clear the field” due to the appearance of superconductivity. A deeper understanding of this mechanism can help control superconductivity.
This study shows the potential of coherent soft X-rays to study spatially heterogeneous materials, especially those in which new functions arise from this spatial heterogeneity. Correlated spectroscopy with lasers has been used for decades, for example, to study the motion of colloids in solution. Converted to soft X-rays, this technique can be used to track magnetic fluctuations, such as spatial and temporal electronic and chemical disorders.
The experiments described here were conducted at Advanced Light Source ALS in California.
For future X-ray sources, such as BESSY III, which generate coherent X-ray emissions that are orders of magnitude stronger than current sources, extend this technique to faster fluctuations and shorter length scales to observe the effect. Will be possible. It’s something I couldn’t achieve before.
The first study of nickelate magnetism found a strong kinship with cuprate superconductors.
For more information:
Alessandro Ricci et al, Measurement of Spin Dynamics of Layered Nickate Using X-ray Photon Correlation Spectrometry: Evidence of Intrinsic Instability of Inconsistent Stripes at Low Temperature, Physical review letter (2021). DOI: 10.1103 / PhysRevLett.127.057001
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