One of the key properties of superconducting materials is their critical temperature: the temperature at which resistance drops to zero. High-temperature superconductivity generally refers to the occurrence of this behaviour at temperatures above 77 K, which enables experimentation and systems to be investigated using liquid nitrogen cooling. Superconducting materials have already been deployed in a wide range of applications, including particle accelerator magnets and medical imaging systems. It is hoped that, in the future, superconductors can be used in areas such as power generation, transmission and storage, as well as in spintronic and quantum device applications. However, the low temperatures, and thus energy needed to enable superconducting behaviour, continues to place many of these applications out of reach.
In the search for new high-temperature superconducting materials, Ranga Dias and colleagues at the University of Rochester and the University of Nevada Las Vegas now report a carbonaceous sulfur hydride system with a highest critical temperature of 287.7 K or about 15 °C. The system was synthesized using a photochemical technique in which the constituent materials are combined in a diamond anvil cell and exposed to 532-nm laser light at pressures of 4 GPa. The superconducting behaviour only occurs at very high pressures of 140–275 GPa, and the exact stoichiometry and structure of the material remains unclear. However, the discovery will be of substantial value to both theoretical and applied researchers, and their search for practical room-temperature superconducting materials.
At a very different scale, Zachary Hartwig and colleagues at Massachusetts Institute of Technology, Commonwealth Fusion Systems, CERN and the Victoria University of Wellington have now demonstrated a high-temperature superconductor cable design for use in high-field d.c. magnets. The cable consists of a central extruded channel for carrying cryogenic coolant, which is surrounded by stacked runs of high-temperature superconductors in a twisted formation. The design overcomes a number of key challenges, namely performance stability under mechanical and thermal cycling, cryostability and the reliable detection of quench or thermal runaway events, and manufacturability. The researchers note that their cable can enable high-field superconducting magnets with strengths beyond 15 T, suitable for fusion energy research or as detector magnets for use in high-energy physics collider experiments.