At issue is how can we produce the best superconductors that remain superconducting even at the highest possible temperatures and ambient pressure? Vienna University of Technology with collaboration from Japan show there is a ‘Goldilocks zone’ of superconductivity where palladium-based materials (‘palladates’) could be the solution.
A new age of superconductors may be about to begin: In the 1980s, many superconducting materials (called cuprates) were based on copper. Then, nickelates were discovered – a new kind of superconducting materials based on nickel.
It is one of the most exciting races in modern physics. In recent years, a new era of superconductivity has begun with the discovery of nickelates. These superconductors are based on nickel, which is why many scientists speak of the “nickel age of superconductivity research.” In many respects, nickelates are similar to cuprates, which are based on copper and were discovered in the 1980s.
Schematic image of the energy levels for copper (Cu2+), nickel (Ni+), palladium (Pd+) superconductors. Image Credit: TU Wien. For more information click the press release or study links.
Now a new class of materials is coming into play. In a cooperation between TU Wien and universities in Japan, it was possible to simulate the behavior of various materials more precisely on the computer than before. There is a “Goldilocks zone” in which superconductivity works particularly well. And this zone is reached neither with nickel nor with copper, but with palladium. This could usher in a new “age of palladates” in superconductivity research.
The results have been published in the scientific journal Physical Review Letters.
The search for higher transition temperatures
At warm temperatures, superconductors behave very similar to other conducting materials. But when they are cooled below a certain “critical temperature,” they change dramatically, their electrical resistance disappears completely and suddenly they can conduct electricity without any loss. This limit, at which a material changes between a superconducting and a normally conducting state, is called the “critical temperature.”
Prof. Karsten Held from the Institute of Solid State Physics at TU Wien said, “We have now been able to calculate this “critical temperature” for a whole range of materials. With our modeling on high-performance computers, we were able to predict the phase diagram of nickelate superconductivity with a high degree of accuracy, as the experiments then showed later.”
Many materials become superconducting only just above absolute zero (-273.15°C), while others retain their superconducting properties even at much higher temperatures. A superconductor that still remains superconducting at normal room temperature and normal atmospheric pressure would fundamentally revolutionize the way we generate, transport and use electricity.
However, such a material has not yet been discovered. Nevertheless, high-temperature superconductors, including those from the cuprate class, play an important role in technology – for example, in the transmission of large currents or in the production of extremely strong magnetic fields.
Copper? Nickel? Or Palladium?
The search for the best possible superconducting materials is difficult. There are many different chemical elements that come into question. You can put them together in different structures, you can add tiny traces of other elements to optimize superconductivity.
Prof. Held noted, “To find suitable candidates, you have to understand on a quantum-physical level how the electrons interact with each other in the material.”
This showed that there is an optimum for the interaction strength of the electrons. The interaction must be strong, but also not too strong. There is a “golden zone” in between that makes it possible to achieve the highest transition temperatures.
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