Understanding Quantum Problem in Superconductors

SLAC National Accelerator Laboratory researchers have discovered that nickel oxide superconductors contain a phase of quantum matter, known as charge density waves, which is common in other unconventional superconductors. The new study shows that nickel oxide superconductors, which conduct electricity without loss at higher temperatures than conventional superconductors, contain a type of quantum matter called charge density waves, or CDWs, that can accompany superconductivity. In other respects, it is surprisingly unique. unconventional superconductors It contains a mixture of strange quantum states. The researchers found one of them – frozen electron ripples known as charge density waves – in a nickel superconductor they discovered three years ago.

The illustration shows a type of quantum material called charge density waves, or CDWs, superimposed on the atomic structure of a nickel oxide superconductor. (Bottom) Nickel oxide material, nickel atoms in orange and oxygen atoms in red. (Top left) CDWs appear as a pattern of frozen electron ripples, with higher electron density at the tops of the ripples and lower electron density at the bottoms. (Top right) This region depicts another quantum state, superconductivity, which can also appear in nickel oxide. The presence of CDWs shows that nickel oxides are capable of forming bound states – an “electron soup” that can host a variety of quantum phases, including superconductivity. Image Credit: Greg Stewart/SLAC National Accelerator Laboratory. Click here for a larger view.

The presence of CDWs shows that these newly discovered materials, also known as nickel, are capable of forming bound states – an “electron soup” that can host a variety of quantum phases, including superconductivity, Researchers from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University report in Nature Physics.

Wei-Sheng Lee, a principal scientist and SLAC investigator at Stanford Institute for Materials and Energy Sciences (SIMES) who led the study, said, “Unlike any other superconductor we know, CDWs appear even before we impregnate materials by replacing some atoms with others to change the number of Electrons that can move freely. This makes nickel an interesting new discipline – a new playground for the study of unconventional superconductors.”

nickel and copper

In the 35 years since the discovery of the first unconventional “high-temperature” superconductors, researchers have been racing to find a conductor that can carry electricity without losing it at room temperature. This would be a revolutionary development, allowing for things like fully efficient power lines, maglev trains, and a host of other energy efficient future technologies.

But while robust global research efforts have identified many aspects of their nature and behaviour, people still don’t know exactly how these materials become superconducting.

So the discovery of nickel’s superconducting forces by SIMES investigators three years ago was exciting because it gave scientists a new perspective on the problem.

Since then, SIMIS researchers have discovered the electronic structure of nickels – the way their electrons behave – and magnetic behavior. These studies revealed similarities and slight differences between nickel and oxides of copper or copper – the first high-temperature superconductors ever discovered and still hold the world record for high-temperature operation at everyday pressures.

Since nickel and copper sit next to each other in the periodic table of the elements, scientists were not surprised to see the kinship there, and in fact they suspected that nickel might make good superconductors. But it turned out to be very difficult to build materials with only the right properties.

“This is still very new,” he told me. “People are still struggling to fabricate thin films from these materials and to understand how different conditions can affect the underlying microscopic mechanisms related to superconductivity.”

frozen electron ripples

CDWs are just one of the strange states of matter jostling for prominence in superconducting materials. You can think of them as a pattern of frozen electron ripples superimposed on the atomic structure of the material, with a higher density of electrons at the tops of the ripples and a lower density of electrons at the bottoms.

When researchers adjust the temperature of the material and the level of doping, different states appear and vanish. When conditions are just right, a material’s electrons lose their individual identities and form an electron soup, and quantum states such as superconductivity and CDWs can emerge.

A previous study by SIMES did not find CDWs in nickel containing the rare element neodymium. But in this latest study, the SIMES team created and examined a different nickel material in which neodymium was replaced by another rare earth element, lanthanum.

Matteo Rossi, who led the experiments while a postdoctoral researcher at SLAC noted, “The emergence of CDWs may be very sensitive to things like stress or turbulence in their surroundings, which can be tuned using various rare earth elements.”

The team conducted experiments with three X-ray light sources – the Diamond Light Source in the UK, the Stanford Synchrotron Radiant Light Source at SLAC and the Advanced Light Source at the Department of Energy’s Lawrence Berkeley National Laboratory. Each of these facilities provided specialized tools for examining and understanding materials at a basic level. All trials had to be conducted remotely due to epidemiological restrictions.

‘Basically self-doping’

Experiments have shown that these nickels can host both CDWs and superconducting states of the material – and that these states existed even before the material was doped. This was surprising, because doping is usually an essential part of getting materials to superconduct.

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He told me that the fact that this nickel is essentially a self-activating factor makes it significantly different from cuprate. “This makes nickel an interesting new system for studying how these quantum phases compete or entangle each other,” he said. “This means that a lot of the tools used to study other unconventional superconductors may be relevant to this as well.”

The samples used in this study were manufactured in the laboratory of Stanford and SLAC Professor and Director of SIMES Harold Hwang. Major funding came from the Department of Energy’s Office of Science. The Stanford Synchrotron Radiant Light Source and Advanced Light Source are user facilities of the Department of Energy’s Office of Science.

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Superconductors share a situation like fusion, for decades, learn a lot and no products yet. But this is not surprising, both fields are located in the subatomic region of matter. Your humble writer first experienced the quantum world as quantum mechanics, mostly as an exercise in mathematics.

Four decades of research, tool development, and experimentation have built a large knowledge base that has transformed the quantum world into something that, over time, is likely to make huge changes to the lives we live. The potential for quantum properties to become a part of innovation, design and engineering is getting closer and we are approaching it faster.

This opinion may seem overly optimistic, but the time period between changes appears to be reduced.

Written by Brian Westinghouse via New Energy and Fuel

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