Between opposition and symmetry

Superconductivity is expressed in the absolute absence of resistance to the passage of an electric current in a material. The possible applications of superconductors range from long-distance transmission of electrical energy without losses, to trains that hover above tracks, without friction

Every good story has deep roots and a bright future. In this case, the warning (fictional) future is described in the book "The World of the Ring" by the author "Hugo" award winner, Larry Niven. The ring world is built on the idea of ​​the physicist Freeman Dyson, who claimed that the way to discover intelligent civilizations in the universe is by searching for "giant spheres that they will form around their suns (instead of looking for planets that are relatively few and have a small area)". Niven's heroes explore the world of the ring, and among other things, they discover in it, in the living area of ​​the ring builders (who have disappeared), various facilities based on superconducting materials that work at room temperature. These materials, explains Niven, are the outstanding proof of the supreme scientific level of the ring's builders. The roots of the story go back to 1911, when Heike Kamerling Onnes discovered the phenomenon of superconductivity (another work of his later earned him the Nobel Prize in Physics).

Superconductivity is expressed in the absolute absence of resistance to the passage of an electric current in a material. The possible applications of superconductors range from the transmission of electrical energy over long distances without losses, to trains that float above the tracks, without friction, which enables fast movement with reduced fuel consumption (this application is based on the fact that superconductors repel magnetic fields). The problem is that superconductivity takes place at very low temperatures - close to absolute zero. About 30 years ago, superconductors were discovered at relatively high temperatures: minus 137 degrees Celsius "only". But all attempts to improve this result did not go well.

Why does superconductivity "break down" when the material is heated above minus 137 degrees? no one knows In fact, we do not understand the reasons and the mechanisms that create the superconductivity at relatively high temperatures. The scientists believe that understanding the reasons for this will advance the ability to develop superconductors that operate at higher temperatures, which may allow simpler applications of superconductors.

In their attempts to understand the origins of superconductivity, Prof. Dan Shahar and research student Mouz Ovadia, from the Department of Condensed Matter Physics at the Weizmann Institute of Science, began to "spoil" superconductors, with the aim of discovering the exact point at which they lose this property. If they understand what causes the loss of the property, they may formulate new insights regarding the causes of the appearance of superconductivity.

There are different ways to spoil a superconductor. One of them is based on the destruction of special particles present in superconductors, which are called "Cooper pairs". They consist of pairs of electrons that together form a kind of one particle, and when the "Cooper pairs" are destroyed, the superconductor loses its superconductivity property.

Another way is based on the "special relationship" that exists between superconductors and magnetic fields that penetrate into them as a kind of tiny current eddies, each of which contains a weak magnetic flux in the center. Under optimal conditions, these vortices are organized at equal distances from each other, in a configuration reminiscent of the arrangement of molecules in a solid crystal. However, under certain conditions, the "melting" of the "crystal" may occur, so that the eddies will move to a state of disorder, reminiscent of the structure of the material when it is liquid. When the eddies become "liquid" and begin to "flow" - the superconductor loses its conductivity property. It is possible to "spoil" a superconductor even when various impurities are introduced into it, and also when it is heated. But Prof. Shahar and Mouz Ovadia chose to do this by activating a strong magnetic field. They slowly changed the strength of the magnetic field and the temperature, and discovered that in a certain combination, the material completely loses the ability to conduct an electric current. In other words, they discovered the existence of a phenomenon that can be called "super-isolation". At this stage it is a feature that exists at very low temperatures, close to absolute zero, but if a way is found to create super insulators that will operate at room temperature, it will be possible to use them, among other things, to produce transistors that do not lose electricity, as well as batteries and electric accumulators that will operate for a much longer time compared to those that stand available to us today.

In a recent study by the scientists, which was published in the scientific journal Nature Physics, they reported that the difference between the state of a superconductor and the state of a superinsulator is quite small, and that the transition between them is fast. This is a kind of similarity and closeness between opposites which reminds, perhaps, the well-known closeness between love and hate.

What is the meaning of this closeness? The scientists began to slowly apply a magnetic field to a superconductor and a superinsulator. Thus they discovered that at a certain point there is an equality between the degree of electrical conductivity of an insulator and the degree of insulation of a conductor.

In the superconducting state, the magnetic vortices are locked, while the "Cooper pairs" flow. In an isolated state, the situation is reversed: the "Cooper pairs" are organized and locked, while the magnetic vortices flow. But the scientists discovered that at the point where there is equality between the conductivity of the insulator and the degree of insulation of the conductor, there is a certain symmetry in the "strange pairing" between the "Cooper pairs" and the magnetic vortices. Understanding this symmetry, or this dependence, the scientists hope, may reveal, in one of their next studies, a profound feature of the phenomenon of superconductivity, and perhaps of superinsulation.