As researchers build on past milestones or breakthroughs, the field continues to edge closer to practical, high-temperature superconductors that could transform industries and everyday life
By Kiran N. Kumar
Tokyo Metropolitan University researchers, led by Associate Professor Yoshikazu Mizuguchi, have developed a groundbreaking superconducting material by combining iron, nickel, and zirconium. This new polycrystalline alloy exhibits superconducting properties, a first for this combination of elements, even though its individual components—iron zirconide and nickel zirconide—are non-superconducting in crystalline form.
Superconductors, which eliminate electrical resistance, have already revolutionized industries such as medical imaging, maglev transportation, and power transmission. New materials may help scientists meet one of today’s biggest challenges: building superconductors that operate at normal temperatures and pressures. Scientists worldwide are pursuing such materials that could show superconductivity at “very high” temperatures — closer to room temperature without requiring super-cooling.
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Using a technique called arc melting, the Japanese team varied the ratios of iron to nickel in the alloy. The resulting material retained the crystal structure of tetragonal transition-metal zirconides, a group of compounds known for their potential in superconductivity. Crucially, the team identified a “dome-shaped” phase diagram in the alloy, where the superconducting transition temperature rises and then falls, a key hallmark of unconventional superconductors. The findings are published in the Journal of Alloys and Compounds.
Unconventional superconductivity
For decades, scientists have sought materials that exhibit superconductivity at higher temperatures, ideally above 77 Kelvin, where liquid nitrogen can replace liquid helium as a coolant. This pursuit has led to discoveries like iron-based superconductors in 2008 and high-pressure hydrogen sulfide superconductors in the mid-2010s, but understanding the mechanism behind high-temperature superconductivity remains one of the greatest challenges in condensed matter physics.
Unlike conventional superconductors, high-temperature superconductors are thought to operate via different mechanisms. Hypotheses such as spin fluctuations and electron pairing mediated by short-range spin waves have gained traction. Materials with magnetic elements or magnetic ordering, like the newly-found iron-nickel-zirconium alloy, are believed to be crucial in achieving unconventional superconductivity.
The Tokyo team’s experiments revealed that the lattice constants, or the lengths of repeating unit cells, change smoothly with the iron-to-nickel ratio. They also observed a magnetic-transition-like anomaly in nickel zirconide, suggesting a link between magnetic ordering and the emergence of unconventional superconductivity.
However, further experiments using single crystals are needed for concluding the correlation, wrote the team in their research paper. In “the absence of bulk superconductivity in the Fe-rich region, we have no explanation at present, but we assume that the disappearance of bulk superconductivity would be related to strong spin fluctuations and/or the transition to a collapsed tetragonal phase. To clarify that, further structural, electronic, and magnetic properties should be investigated.”
Recent controversy to discovery
But the search for high-temperature superconductors has been fraught with controversy and breakthroughs. In 2020, a paper in Nature described a hydrogen-carbon-sulfur compound that demonstrated superconductivity at room temperature (288 K) but required extreme pressures of around 270 gigapascals. The study initially garnered significant attention, but questions about the validity of its background subtraction procedures led the journal to retract the article. Despite this, the authors maintained that their raw data strongly supported the claims.
Fast forward to 2023, a new controversy emerged when a group of scientists published a study claiming the discovery of a lutetium-based superconducting material capable of operating near ambient temperature and pressure. The bold claim triggered widespread debate, with many researchers expressing skepticism. Among them was Adam Denchfield, who decided to investigate further by revisiting past studies on rare earth trihydrides.
Denchfield found that rare earth trihydrides, first studied in the 1960s, exhibited unusual changes in electrical conductivity when cooled — a phenomena that remained unexplored. Building on these findings, he discovered that specific arrangements of lutetium atoms combined with hydrogen and nitrogen could lead to high-temperature superconductivity.
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Not content to stop with lutetium, Denchfield explored the potential of other rare earth elements, such as yttrium and scandium, which are chemically similar to lutetium. His simulations identified three promising cubic structures capable of superconductivity. These designs, outlined in his paper, could achieve critical temperatures above 200 Kelvin (-100°F). Denchfield believes some of these structures might even unlock superconductivity at room temperature and ambient pressure—an achievement often referred to as the “holy grail” of the field.
As researchers build on past milestones or breakthroughs, the field continues to edge closer to practical, high-temperature superconductors that could transform industries and everyday life.