Superconductor Breakthrough: Scientists Discover an Invisible Phenomenon

With more understanding of the connection between spin liquids and superconductivity, it may be able to create superconductors that function at room temperature, which would revolutionize our way of life.

For technologies like high-speed hovertrains, MRI equipment, effective power lines, quantum computers, and others, superconductors hold great technical and financial promise. However, as superconductivity needs extremely low temperatures, their usefulness is constrained. Because of this demanding and expensive requirement, integrating them with current technology is quite difficult.

In contrast to regular metallic conductors, whose resistance decreases gradually as temperature is decreased, even down to close to absolute zero, superconductors have a specified critical temperature beyond which it abruptly drops to zero.

The main goal of modern superconductivity research is to find superconductors that don't require such low temperatures. The major unsolved question in this discipline relates to the process by which these superconductors work. More useful uses may be made if superconductivity's high-temperature production process was understood.

This ongoing riddle has been partially solved by a new study that was carried out by researchers at Israel's Bar-Ilan University and just published in the journal Nature. The researchers captured a behavior using a scanning SQUID (superconducting quantum interference device) magnetic microscope that was previously unobservable.

When high-temperature superconductors were first discovered, scientists were astounded. Scientists had predicted that metals would exhibit good superconductivity. It was discovered that insulating ceramic materials provide for the best superconductors, contrary to expectations.

It may be possible to pinpoint the origin of these ceramic materials' superconductivity and have better control over the critical temperature by identifying characteristics that these ceramic materials share. One of these characteristics is the strong interfacial resistance of the electrons in these materials. Therefore, they are unable to move at will. Instead, they are imprisoned within a periodic lattice framework.

Two characteristics distinguish electrons: their charge (a moving charge generates an electric current), and their spin. The magnetic properties of electrons are due to their quantum feature, called spin. Each electron appears to have a small bar magnet linked to it. In common materials, the charge and spin of the electrons are "built-in" and cannot be altered.

However, interactions between the electrons in particular quantum materials known as "quantum spin liquids" permit a remarkable phenomena whereby each electron is split into two particles, one with charge (but no spin) and one with spin (and no charge). These quantum spin liquids could occur in high-temperature superconductors, which would explain why these materials have such good superconductivity.

The difficulty is that traditional measures "invisible" these spin liquids. There is no experiment that could confirm or go deeper into a material's composition, even when we assume it might be a spin liquid. This is comparable to dark matter, which is extremely challenging to detect because it doesn't interact with light.

The recent research, carried out by Professor Beena Kalisky, Ph.D. student Eylon Persky, and their collaborators from the Physics Department at Bar-Ilan University, represents an important step in the creation of a technique to analyze spin liquids. The interaction of a spin liquid with a superconductor was used by the researchers to investigate its characteristics. They employed a manufactured substance comprised of alternating atomic layers of the candidate spin liquid and superconductor.

Superconductors, in contrast to spin liquids, which produce no signals, have distinct magnetic signatures that are simple to detect. By detecting the minute changes the spin liquid caused in the superconductor, we were able to learn more about its characteristics, said Persky. To examine the characteristics of the heterostructure, the researchers utilized a scanning SQUID, an incredibly sensitive magnetic sensor that can detect both magnetism and superconductivity.

"We have seen the superconductor generate vortices. Electric currents are circulating within these vortices, and each one contains a quantum of magnetic flux. In our situation, the vortices formed naturally, but providing a magnetic field is the sole technique to produce such vortices, says Kalisky. This discovery demonstrated that the magnetic field was produced by the substance itself. That this field did not manifest itself in a direct measurement was the biggest surprise. Unexpectedly, Kalisky continues, "we discovered that the magnetic field produced by the material was invisible to a direct magnetic measurement.

The findings indicated the existence of a "hidden" magnetic phase that was made visible during the experiment by interacting with the superconducting layer. The research team, which included members from Bar-Ilan University, the Technion, the Weizmann Institute, the University of California, Berkeley, and the Georgia Institute of Technology, came to the conclusion that the interaction between the spin liquid layer and the superconducting layer was likely the cause of this magnetic phase. The spin-charge separation in the spin liquid is what causes the hidden magnetism. Without a "real" magnetic field, the superconductor responds to this magnetism and creates vortices.

In fact, this is the first time that the connection between these two phases of matter has been directly observed. The characteristics of the mysterious spin liquids, such as the interactions between the electrons, are now accessible thanks to these findings. The findings also allow for the development of new layered materials that might be used to study the interaction between superconductivity and other electronic phases. It may be possible to build superconductors that operate at room temperature with further research on the relationship between spin liquids and superconductivity, which would transform our daily life.

By BAR-ILAN UNIVERSITY