What are the properties of superconductors

Hydrogen influences the properties of superconductors

The search for promising superconductors that can conduct electrical current without resistance even at high temperatures is difficult. Researchers at the Vienna University of Technology (TU Wien) have now found that hydrogen influences the electronic properties of superconductors.

As soon as hydrogen is included in the manufacture of nickelate superconductors, the material is not superconducting.

Photo: panthermedia.net/Sashkin7

"High-temperature superconductivity is an extremely complex and difficult research area," emphasizes Karsten Held, professor at the Institute for Solid State Physics at the Vienna University of Technology. This can be seen, for example, in the fact that a group of scientists from Stanford published spectacular results, which, however, could not be reproduced by any other researchers and thus also not confirmed. The Stanford team announced a new era for high-temperature superconductivity in the summer of 2019. The scientists justified this with the discovery of so-called nickelates, a special class of materials with the properties of superconductors. So you could conduct electrical current without any resistance even at high temperatures.

Researchers at TU Wien have now found out why the results from the USA could not be repeated. This is due to the fact that with some nickelates additional hydrogen atoms are built into the structure of the material. This addition changes the behavior of the material. This effect must therefore be taken into account when manufacturing new superconductors.

Sensitive to hydrogen

“For a long time the focus was particularly on so-called cuprates, that is, compounds containing copper. We therefore also speak of the copper age, ”explains Karsten Held. “They made some important advances, even if there are still many unanswered questions in the theory of high-temperature superconductivity.” In the past, researchers had found that some materials only have a superconducting function near absolute temperature zero. Due to this, however, these cannot be used at all for technical applications. For decades, scientists have therefore been looking for materials that have this special property even at higher temperatures. So-called “high-temperature superconductors” were discovered in the 1980s. The name is misleading because the high-temperature superconductors also have to be cooled to a great extent in order to maintain their special superconducting properties. However, it was important for the researchers to find superconductors at higher temperatures.

This research concentrated for the first time on ferrous superconductors. This also resulted in the result of the Stanford scientists. At the Vienna University of Technology, the nickelates were now analyzed with the help of supercomputers. The result: You are extremely sensitive to hydrogen. Hydrogen atoms can, for example, be incorporated into certain nickelates during synthesis. The result: The electronic properties of the material change completely. "However, this does not happen with all nickelates," says Liang Si from the Vienna University of Technology. “Our calculations show that for most of them it is energetically cheaper to incorporate hydrogen, but not for the nickelates from Stanford. Even minor changes in the synthesis conditions can make a difference. ”On April 24, 2020, a group of researchers from the National University of Singapore (NUS Singapore) used these findings from the Vienna University of Technology to produce superconducting nickelates. This succeeded because they let the released hydrogen escape during production.

Supercomputers help to find superconductors

In order to continue researching the properties of nickelates and to be able to better understand and predict them, the scientists at the Vienna University of Technology are developing and using new computer calculation methods. "Since a large number of quantum physical particles play a role here at the same time, calculations are extremely time-consuming," explains Liang Si. “By combining different methods, we are now even able to estimate the critical temperature up to which the various materials are superconducting. Such reliable calculations have not been possible until now. ”Specifically, the team calculated the range in which the concentration of strontium in the nickelates is allowed to be so that superconductivity is possible. In another experiment, it was able to confirm these predictions. After the successes, Karsten Held dares to take a look into the future: “The new nickelate superconductors as well as our theoretical understanding and the predictive power of computer calculations open up a whole new perspective of getting closer to the great dream of solid-state physics: a superconductor at ambient temperature without cooling. "

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  • Nina Draese

    Nina Draese studied history and art history (M.A.). Among other things, she has worked for dpa, the press department of BMW, for the car newspaper and the MAV publishing house. She is a freelance journalist and part of the Content Qualitäten team. Your topics: automotive, energy, climate, AI, technology, environment.