High critical temperature superconductors - Physics and applications

Today's technology is largely based on the mastery of semiconductor materials, from which transistors and electronic circuits are manufactured with increasing integration - several billion transistors per chip - as well as detectors and transmitters of electromagnetic waves, from radio waves to visible light. There isn't an economic or industrial sector today that doesn't incorporate these "Information and Communication Technologies" (ICT).

However, behind this undisputed domination, semiconductor devices have their downside and, above all, their limits, some of which have already been reached. These are essentially due to the fact that a semiconductor device has a finite resistance, which dissipates energy by the Joule effect under the action of a current, on the one hand, and limits the bandwidth in components incorporating a capacitor (low-pass RC filter), on the other. The massive use of digital technologies is therefore accompanied by increasing energy consumption. This is a major energy and environmental challenge. We therefore need to find more energy-efficient ways of processing information, and if possible at higher frequencies. This can be achieved by changing the basic architecture of processors, to bring them closer to the way the brain works, which is particularly energy-efficient (neuromorphic systems), or by changing the very nature of information processing, using quantum coherence processes (quantum computers). Another avenue is to take advantage of the properties of superconducting materials, which dissipate very little energy, and can support quantum information processing.

Devices based on metals and/or semiconductors also have limitations when it comes to detecting electromagnetic waves. The Johnson noise associated with any resistance imposes a physical limit on device sensitivity and detectivity. Using low-dissipation superconducting materials would be an asset for progress in this area too.

The High Critical Temperature (SHTc) superconducting materials presented in this article are interesting alternatives for overcoming the limits described above, at least in a number of areas. Discovered in 1986, these complex copper-based oxides (cuprates) are superconductors at temperatures above that of liquid nitrogen (77 K), unlike conventional superconductors which are superconductors at that of liquid helium (4.2 K). Cryogenic systems that produce temperatures in the 77 K range cost much less than their 4.2 K equivalents, and are much simpler and more miniaturizable.

Unlike conventional superconductors, which are metals, SHTc are oxides, with a complex crystallographic structure that plays a key role in their electronic properties. These properties differ from those of conventional metals, and are...