The investigation is a step toward becoming much more accessible superconductivity.
With additional knowledge of the interaction between spin liquids and superconductivity, it may be possible to develop superconductors that operate at room temperature. This would transform our daily lives.
Superconductors provide enormous technological and economic value for high-speed hovertrains, MRI machines, efficient power lines, quantum computing, and other applications. However, their usefulness is limited due to the fact that superconductivity requires extremely low temperatures. It is highly difficult to integrate them with modern technology because to this demanding and costly requirement.
The electrical resistance of a superconductor has a specific critical temperature beyond which it suddenly drops to zero, unlike an ordinary metallic conductor, who starts declining gradually as temperature drops below absolute zero.
The primary objective of current superconductivity research is to find superconductors that do not require such low temperatures. The mechanism by which these superconductors operate is the biggest mystery in this field, to which no one has an answer. Understanding the mechanism that produces superconductivity at high temperatures would allow for more practical applications.
A recent research undertaken by scientists at Israel's Bar-Ilan University and recently published in the journal Nature makes significant progress in unraveling this ongoing mystery. A previous discovery had been unveiled by other techniques.
When high-temperature superconductors were first discovered, scientists were surprised. Metals were assumed to have excellent superconductivity, but instead, it was discovered that insulating ceramic materials are the finest superconductors.
Finding common characteristics in these ceramic materials might help identify where their superconductivity originated and improve control over the critical temperature. One such feature is that the electrons in these materials are unable to move freely. They are instead trapped inside a periodic lattice structure.
Electrons have two defining characteristics: their charge (a moving charge produces an electric current) and their spin. Spin is the quantum property of electrons responsible for their magnetic properties. It is as if a tiny bar magnet is attached to each electron.
Interactions between the electrons allow for a unique phenomenon whereby each electron is broken into two particles, one with charge (but no spin) and one with spin (but no charge). Such quantum spin liquids may exist in high-temperature superconductors, and their existence might explain why the superconductivity in these materials is so good.
The problem is that these spin liquids are "invisible" to conventional measurements. Even when we suspect a material to be a spin liquid, there is no method that can verify it or probe its existence. This is similar to dark matter, which does not interact with light and is therefore difficult to detect.
The present investigation, conducted by Professor Beena Kalisky and doctoral student Eylon Persky from the Physics Department at Bar-Ilan University, is a significant step towards the development of a novel spin liquid investigation technique. The researchers used an engineered material made of two different atomic layers of the superconductor and the candidate spin liquid.
Superconductors have clear magnetic signatures that are easy to measure, unlike spin liquids that do not generate any signals, according to Persky. We were therefore able to investigate the properties of the spin liquid by measuring the small changes it caused in the superconductor, according to the researchers.
The greatest surprise came when the material itself generated a magnetic field, according to Kalisky.
Researchers concluded that the "hidden" magnetic phase was probably a direct result of the interaction with the spin liquid layer at the Georgia Institute of Technology. The hidden magnetism is a result of the spin-charge separation in the spin liquid, which generates vortices without the need for a "real" magnetic field.
This is the first direct observation of the relationship between these two phases of matter. These findings provide insight into the elusive spin liquids, as well as their interactions with other electrons. Additional research may enable the design of superconductors that operate at room temperature.
Eylon Persky, Anders V. Björlig, Irena Feldman, Ehud Altman, Itamar Kimchi, Jonathan Ruhman, Amit Kanigel, and Beena Kalisky, Nature. DOI: 10.1038/s41586-022-04855-2.