The researchers succeeded in creating a unidirectional superconductor

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A team from Delft University of Technology in the Netherlands has recently done what has been considered impossible so far: they have succeeded in designing a superconductor that only allows current to flow in one direction. This discovery could pave the way for a new generation of computers and electronic devices where this property is essential.

The phenomenon of superconductivity was discovered in 1911 by physicist Heike Kamerlingh Onnes. By definition, a superconductor is able to handle electricity without any resistance, so there is no loss of power. In other words, with a superconductor, current can theoretically flow almost indefinitely, since energy is not lost. It also has the property of completely dissipating the magnetic field around it. The event occurs at very low temperatures, close to absolute zero, and is based on the formation of pairs of electrons (called “Cooper pairs”).

In contrast, in a standard electrical or electronic circuit, when current is flowing, electrons encounter some resistance as they move (due to interaction around atoms); therefore, part of the electrical energy is lost in the form of heat. This is also the reason why electrical appliances can be hot to the touch after a few minutes of operation. If these devices operate based on superconductors, they will not only be more efficient, but much more economical in terms of electricity.

Two superconductors separated by a quantum material

Superconductors can make electronics hundreds of times faster, and their implementation can make computing more “green”. According to the Dutch Research Council (NWO), using superconductors instead of ordinary semiconductors can save up to 10% of all energy reserves in the West. To do this one day, however, superconducting electrons will have to move only in one direction in circuits, because this is how computing and electronics work – a seemingly impossible challenge.

Professor Mazhar Ali and his research team from the Technical University of Delft still achieve this success, which is very remarkable: it is like inventing a kind of ice where it is only possible to skate one by the way! ” If the 20th century is the century of semiconductors, the 21st will be a century of superconductors. “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 combining small amounts of impurities into the material to create an excess or deficiency of electrons. Different doped semiconductors can be contacted to form junctions: ” The classic example is the famous “pn junction”, where two semiconductors are connected: one has more electrons (-) and the other has more holes (+). The charge separation creates an embedded net potential that can be felt by an electron passing through the system. This can break symmetry and produce ‘one way’ properties “said Ali.

It is never possible to obtain a similar behavior without a magnetic field with superconductors, which always conduct current in both directions and have no integrated potential. But Ali and his team came up with an idea to use “quantum material Josephson junctions”. Josephson junctions are assemblies of two superconductors, separated by a non-superconducting insulating or metallic material; This time they chose a two-dimensional quantum material (such as graphene), with the formula Nb3Br8-which is part of the group of new quantum materials created by a team from Johns Hopkins University, in the United States.

Other challenges to be overcome before a commercial application

The theory suggests that Nb3Br8 hosts a sharp electric dipole. Relying between two layers of niobium penyelenide (NbSe2), it makes it possible to create a junction that can be superconductive with a positive current, while resistive to a negative current.

To confirm their results, the researchers tried to “move” the diode, using the same magnitude current in the same direction. They therefore show that they do not measure resistance (superconductivity) in one direction, but actual resistance (normal conductivity) in the other. They also ensured that the effect occurred only in the complete disappearance of a magnetic field – a particularly important point, because the nanoscale magnetic field is very difficult to control and limit, the scientist pointed out.

Therefore, a technology that was previously only possible in semiconductors can now be achieved in superconductors. This new approach could make it possible to make computers 300 to 400 times faster than today’s computers. There remains, however, a challenge to be encountered before considering a commercial application: raising the operating temperature at the junction (the superconductor used in this study requires temperatures below -266 ° C).

We want to work now with a well-known so-called “high critical temperature” superconductor and see if we can run Josephson diodes at temperatures above 77 K (-196 ° C), as this will allow liquid nitrogen to cool. . “, Ali specified in the press release. Once that is done, we will still have to find a way to make these components on a large scale, the purpose of which is to get chips equipped with millions of Josephson diodes.

Source: H. Wu et al., Nature

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