Electrons don't like each other very much. Their negative charges repel each other, which is nothing personal. It takes a bit of nudging to get them to pair up and travel together.
In old-school superconductors, which were discovered in 1912 and conduct electric current with no resistance, but only at extremely cold temperatures, the nudging comes from the atomic lattice.
Even though newer, "unconventional" superconductors are exciting because of their potential to operate at close to room temperature for things like zero-loss power transmission, no one knows for certain what the nudging is.
The nickel oxides, or nickelates, are an unconventional superconductor family that was created by researchers at the Department of Energy's SLAC National Accelerator Laboratory. They've looked at the nickelates' properties and compared them to one of the most famous unconventional superconductors, the copper oxides.
The magnetic fields in nickelates are always on, unlike in the cuprates.
Magnetism is a question of whether the person is a friend or foe.
The scientists said that nickelates are magnetic as if they were holding a small magnet. This is true whether the nickelate is in its non-superconducting, normal, state or in a superconducting state. Cuprates are notmagnetic in their state.
The study looked at fundamental properties of the nickelates compared to the cuprates and what that can tell us about unconventional superconductors in general.
She said that magnetism and superconductivity compete with each other in this type of system.
The results don't answer the question, but they highlight where more work is needed. They are the first time that magnetism has been looked at in the normal state of nickelates.
"This is an important piece of the puzzle that the research community is putting together as we work to frame the properties and phenomena at the heart of these exciting materials," said Harold Hwang, a professor at SLAC.
The muon entered.
It has been difficult to study the nickelates in this field.
It took a long time for nickelates to host superconductivity because they are so hard to make.
They could only make thin films of the material. A number of research groups around the world are trying to make it easier to synthesise nickelates.
The low-energy muon spin rotation/relaxation method is only available in Switzerland and can be used to measure the magnetic properties of thin films.
Muons are 207 times larger than electrons. They last for 2.2 millionths of a second before they die. Positively charged muons can decay into a positron, a neutrino and an antineutrino. They spin like tops and change their direction in response to the magnetic field. Only in their immediate surroundings can they feel those fields.
Scientists use a beam of muons to put tiny particles in the material they are studying. The muon's spin causes the positrons to fly off in a different direction. Researchers can see which direction the muons were pointing when they winked out of existence by tracing the positrons' origins.
Finding a way to work around it.
The Pandemic made it impossible for the team to travel to Switzerland to do their experiments. At the time, Fowlie was a graduate student at the University of Lausanne and was going to work in the group. She started the first round of experiments in Switzerland with the help of a team led by a senior scientist at PSI.
The team wanted to conduct a second round of experiments after Fowlie arrived. The team was able to return to Switzerland after travel restrictions were lifted.
Scientists are able to put muons at precise depths in the nickelate materials. They were able to figure out what was happening in each nickelate compound with slightly different chemical compositions. The nickel atoms in the layers were magnetic.
There is a lot of interest in the nickelates. Half a dozen research groups have published their own ways of synthesizing nickelates, and a lot of theorists are trying to come up with insights to guide the research in productive directions.
"We are trying to do what we can with the resources we have, but there is still a lot more we can learn and do," he said.
More information: Jennifer Fowlie, Intrinsic magnetism in superconducting infinite-layer nickelates, Nature Physics (2022). DOI: 10.1038/s41567-022-01684-y. www.nature.com/articles/s41567-022-01684-y Journal information: Nature Physics
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