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A team from the University of Technology in Delft, the Netherlands, has just achieved what was previously considered impossible: they have succeeded in designing a superconductor that allows current to flow in only one direction. This discovery could pave the way for a new generation of computers and electronics for which this feature is fundamental.
The phenomenon of superconductivity was discovered in 1911 by the physicist Heike Kamerlingh Onnes. By definition, a superconductor can transmit electricity without resistance, therefore without loss of energy. In other words, with a superconductor, current can theoretically flow almost infinitely, because energy is not diffused. It also has the property of completely dispersing the magnetic field that surrounds it. The phenomenon occurs at very low temperatures, close to absolute zero, and is based on the formation of electron pairs (called “Cooper pairs”).
In contrast, in a typical electrical or electronic circuit, when current flows, electrons face some resistance as they move (due to interactions with the surrounding atoms). Therefore, part of the electricity is lost in the form of heat. This is the reason why electrical appliances warm up to the touch after a few minutes of operation. If these devices were based on superconductors, they would not only be more efficient, but also much more economical in terms of electricity.
Two superconductors separated by a quantum material
Superconductors can make electronics hundreds of times faster and their application would make computers much greener. According to the Dutch Research Council (NWO), using superconductors instead of conventional semiconductors could save up to 10% of all western energy reserves. For this to be possible one day, however, superconducting electrons must only move in one direction in the circuits, because that is how computers and electronics work – a seemingly impossible challenge. It should be noted, given the very high conductivity of the superconductors…
Professor Mazhar Ali and his research team at Delft University of Technology, however, have achieved this feat, which is absolutely remarkable: it’s like inventing a type of ice that can only be skated in one direction! ” If the 20th century was the century of semiconductors, the 21st could be the century of the superconductor “, Said the scientist in a press release.
As the physicist points out, with semiconductors, the problem does not arise: their conductivity can be controlled by doping – which involves incorporating a small amount of impurities into the material to produce an excess or deficit of electrons. Semiconductors with different admixtures can then be contacted to create joints: The classic example is the famous “pn junction”, where two semiconductors are joined together: one has extra electrons (-) and the other has extra holes (+). The charge separation creates a built-in net potential that will be felt by an electron passing through the system. This breaks the symmetry and can create “one way” properties. “says Ali.
It has never been possible to achieve similar behavior without a magnetic field with superconductors, which always carry current in both directions and have no integrated potential. But Ali and his team thought of using “Josephson quantum intersections.” Josephson connectors are two conductor assemblies, separated by a non-superconducting insulating or metal material. this time they chose a two-dimensional quantum material (such as graphene), Nb3Br8 – which is part of a group of new quantum materials developed by a team from Johns Hopkins University in the United States.
Other challenges to overcome before a commercial application
Theory showed that Nb3Br8 housed a sharp electric dipole. Placed in a sandwich between two layers of niobium dienelenium (NbSe2), it made it possible to create a junction that can be superconducting with a positive current, while it is resistant with a negative current.
To confirm their results, the researchers tried to “change” the diode, applying the same magnitude of current in both directions. They thus showed that they did not measure resistance (superconductivity) in one direction, but real resistance (normal conductivity) in the other. They also claim that the phenomenon occurred only in the complete absence of a magnetic field – a particularly important point, as nanoscale magnetic fields are very difficult to control and limit, the scientist points out.
Thus, a technology that was previously only possible with semiconductors can now be achieved with superconductors. This new approach could enable computers to grow 300 to 400 times faster than today’s computers. However, there remains another challenge that must be addressed before considering a commercial application: increasing the operating temperature of the junction (the superconductor used in this study requires temperatures below -266 ° C).
” We now want to work with the well-known “high temperature” superconductors and see if we can operate Josephson diodes at temperatures above 77 K (-196 ° C), as this will allow cooling with liquid nitrogen. “, Ali explains in the press release. In this way, it will still be necessary to find a way to produce these components on a large scale, in order to be able to obtain chips equipped with millions of Josephson diodes.
Source: H. Wu et al., Nature