Researchers at the Delft University of Technology (TU Delft) have realized the superconducting analogue to the semiconducting diode, the Josephson diode. Demonstrated with magnetic-field-free and single directional superconductivity with Josephson coupling, the realization will serve as the building block of the next generation of superconducting circuit technology. Since superconductivity was discovered in 1911, magnetic-field free single-direction superconductivity was thought to be impossible. The New Atlas reported on this discovery, which is expected to increase computing speed by 400% and result in large energy savings. 

The Decline of Moore’s Law

In 1965, Gordon Moore observed that the number of transistors in a dense integrated circuit doubles almost every two years. This observation has come to be known as Moore’s Law. As transistor density increased, the doubling interval fell from two years to 18 months, as the semiconductor industry reaped huge rewards. The twentieth century became the age of the semiconductor. 

However, in recent years, Moore’s Law has begun to slow down, leading to concerns that Moore’s Law is dead. Although Moore’s Law is not dead, it is true that Moore’s Law has begun to reach its limits, affecting the productivity gains that semiconductors have produced and that the economy as a whole has enjoyed. 

Consequently, the impetus to find ways to increase computing speed, has never been greater. That’s where this discovery comes in. Superconductors would allow electronic devices to operate at vastly greater speeds, without loss of energy. However, the problem has been that superconductors charge bi-directionally and use magnetic fields. This has meant that increasing computing speeds with superconductors has not been possible. Single-directionality is fundamental for computing and other electronics. Normal conduction features electrons flying around in the form of separate particles, which move as pairs in superconductors that do not experience any energy loss. In the 1970s, researchers at IBM tried to develop superconducting computing but had to abandon the projection because absent non-reciprocal superconductivity, computers run on superconductors were impossible. 

Past Problems with Superconductors

Scientists have wrestled with superconductivity since its discovery in 1911 by Kamerlingh Onnes, a Dutch physicist. Superconductors allow current to flow through a wire without any resistance, so that current cannot be inhibited or blocked. More importantly, that current cannot be made to flow in one direction or the other. 

Heng Wu and Mazhar Ali and the rest of the TU Delft team, published their results in the prestigious scientific journal, Nature. The team’s results have made superconducting diodes possible and brought the computing industry to the verge of a revolutionary shift in computing speeds and electronics’ energy efficiency. 

In order to realize the Josephson diode, the team fabricated an inversion symmetry breaking van der Waals heterostructure of NbSe2/Nb3Br8/NbSe2. Semiconductors may have a fixed dipole built-in, which makes it more difficult for electrons to move as opposed to the other, but superconductors do not enjoy this potential. Consequently, researchers have been constrained in how they can generate single-directionality. Single-directionality has only been possible through magnetic fields, making it impractical for electronics.

Single-directional superconductivity is a major achievement given the nature of superconductors. A great analogy is that single-directional superconductors are like ice that has no friction in one direction, and insurmountable friction in the other direction. 

The field-free Josephson diode in a van der Waals heterostructure

In order to get past the limitations of superconductors, the team used a new 2D quantum material similar to graphene, Nb3Br8 which is used in atomic layers. Theoretically, it had been proposed that it could have its own electric dipole.

The team developed “Quantum Material Josephson Junctions”, which sandwich atomic layers of Nb3Br8 between two superconductors. This extremely thin sandwich is as thick as a few atomic layers. This was essential for making a Josephson diode and was something that could not be done with typical 3D materials. 

The Benefits of Superconductors

Old types of Josephson Junction superconductors are already the basis of many technologies, such as MRIs, and quantum computing. Technology that ran with semiconductors can now be developed with superconductors, such as computers with as much as a terahertz of speed, 300 to 400% faster than the fastest computers today. We are now entering the age of the superconductor. That is the most obvious advantage of superconductors to electronics. 

Superconductors will also make electronics more eco-friendly. For instance, a superconductive wire stretched out all the way to the moon could transmit energy without any loss. According to the Dutch Research Council (NWO), replacing semiconductors with superconductors could lead to Western energy reserve savings of as much as 10%.

Superconductors will be implemented in supercomputers and server farms first. This is because the world has shifted to a centralized computing model, with intensive computation done in centralized facilities in which localization leads to massive gains in heat and power management, and other areas. Existing technology can be adapted to Josephson diodes. With this, superconductors will revolutionize supercomputing and centralized computation.