Understanding the connection between spin liquids and superconductivity may lead to the creation of room-temperature operating superconductors, which would have far-reaching implications for our daily lives.

High-speed hovertrains, magnetic resonance imaging equipment, efficient power lines, quantum computing, and other technologies could all benefit greatly from the use of superconductors. However, their utility is constrained because of the need for sub-zero temperatures for superconductivity. Given the high bar set by this need, it is difficult and expensive to integrate them with current technology.

Unlike regular metallic conductors, whose electrical resistance decreases gradually as temperature is lowered, even down to near absolute zero, superconductors have a critical temperature beyond which it rapidly drops to zero. The fundamental goal of modern superconductivity research is to find superconductors that do not need to operate at such low temperatures. No one knows how these superconductors actually work, which is the biggest mystery in this area. More useful applications could be achieved by learning what causes superconductivity at high temperatures.

Scientists from Israel’s Bar-Ilan University have made strides toward solving this enigma with new research that was recently published in Nature. The researchers captured images of a phenomena using a scanning SQUID (superconducting quantum interference device) magnetic microscope. When high-temperature superconductors were first discovered, scientists were taken aback. A high degree of superconductivity was thought to be present only in metals by scientists. The best superconductors are, surprisingly, insulating ceramic materials.

The genesis of their superconductivity and the ability to regulate the critical temperature could be uncovered by identifying shared characteristics among these ceramic materials. The strong electron repulsion between atoms in these materials is one such feature. Since this is the case, they are restricted in their mobility. Instead, they are imprisoned within a lattice that repeats at regular intervals.

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Electrons can be distinguished from other subatomic particles by their charge and spin. Electrons’ magnetic characteristics can be attributed to their quantum property known as “spin.” Like a little bar magnet is stuck to the side of every electron. The electrons’ charge and spin are “built-in” (inherent) properties in most materials.

However, a peculiar occurrence is enabled by interactions between electrons in quantum materials dubbed “quantum spin liquids,” wherein each electron is split into two particles, one with charge (but no spin) and one with spin (and no charge). Perhaps the high superconductivity of these materials might be attributed to the presence of such quantum spin liquids in their bulk phase at high temperatures. The problem is that typical instruments can’t “see” these spin liquids. There is currently no experiment that can confirm or investigate the nature of a material’s suspicion to be a spin liquid. It’s hard to detect since it doesn’t interact with light, just like dark matter.

The recent study is an important step toward the creation of a method to investigate spin liquids and was undertaken by Professor Beena Kalisky and PhD student Eylon Persky of the Physics Department at Bar-Ilan University and their collaborators. Scientists put a spin liquid in contact with a superconductor to investigate its characteristics. They resorted to a synthetic material comprised of superconductor and spin liquid candidate atomic layers.

Superconductors, in contrast to signal-free spin liquids, have easily measurable magnetic fingerprints. This allowed us to investigate the spin liquid’s characteristics by monitoring the minute changes it induced in the superconductor, as Persky puts it. SQUID (scanning tunneling microscope) is a highly sensitive magnetic sensor that can detect both magnetism and superconductivity, which was utilized by the researchers to probe the heterostructure’s characteristics.

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We have witnessed the formation of vortices in the superconductor. These whirlpools represent electric currents spinning around, and each one stores a single quantum of magnetic flux. “Normally, you’d need to apply a magnetic field to make these kinds of vortices, but in this case, they formed on their own,” says Kalisky. Due to this finding, it was determined that the magnetic field was produced by the material itself. The fact that this field did not manifest itself in a direct measurement came as the biggest shock of all. “We found that the magnetic field formed by the material was imperceptible to a direct magnetic measurement,” says Kalisky.

This experiment’s interaction with the superconducting layer revealed what the results suggested was a previously “hidden” magnetic phase. Researchers from Bar-Ilan, Technion, Weizmann Institute, UC Berkeley, and Georgia Tech collaborated to determine that the spin liquid layer’s interaction with the superconducting layer was likely responsible for the emergence of this magnetic phase. The spin-charge separation in the spin liquid is responsible for the latent magnetism. Without an external, “actual,” magnetic field, the superconductor will respond to this magnetism and create vortices.

In fact, this is the first time the connection between the two states of matter has been shown directly. The features of the enigmatic spin liquids, such as the interactions between electrons, are now accessible thanks to these findings. The findings also pave the way for further research into the connection between superconductivity and other electronic phases through the fabrication of additional layered materials. The development of room-temperature superconductors would have far-reaching consequences for society, and more research into the connection between spin liquids and superconductivity is needed.

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