Researchers at Ames National Laboratory have achieved a groundbreaking milestone in the realm of superconductors by identifying the inaugural unconventional superconductor boasting a chemical composition naturally occurring in the environment. Amongst the limited selection of minerals exhibiting superconductive behavior when cultured in laboratory settings, miassite emerges as a standout, joining the exclusive league of merely four minerals found in nature with such properties.
Delving into the intricacies of miassite, the team’s exploration illuminated its status as an unconventional superconductor, showcasing traits akin to those witnessed in high-temperature superconductors. This revelation marks a significant stride forward in our understanding and utilization of superconducting materials, promising a myriad of potential applications across various domains of science and technology.
The recent publication in Communications Materials represents a significant advancement in the comprehension of unconventional superconductivity, as detailed by scientists from Ames National Laboratory. This breakthrough stands to catalyze the development of more sustainable and cost-effective superconductor-based technologies in the foreseeable future.
Superconductivity, a phenomenon characterized by the ability of materials to conduct electricity without any energy dissipation, holds immense potential across diverse fields such as medical imaging (MRI machines), power transmission (cables), and quantum computing. While conventional superconductors are well-studied, they exhibit low critical temperatures—the threshold temperature at which a material transitions into a superconducting state.
In contrast, the 1980s witnessed the discovery of unconventional superconductors, distinguished by significantly higher critical temperatures. Notably, all known unconventional superconductors have been synthesized in laboratory settings, prompting the prevailing belief that unconventional superconductivity is solely a product of artificial synthesis. Ruslan Prozorov, a scientist at Ames Lab, underscores this prevailing notion, emphasizing that these materials are exclusively lab-grown.
This prevailing understanding has thus far limited the exploration of natural occurrences of unconventional superconductivity. However, the recent identification of miassite as a naturally occurring unconventional superconductor challenges this notion, opening new avenues for research and potentially reshaping our understanding of superconductivity as a natural phenomenon.
According to Prozorov, the scarcity of naturally occurring superconductors stems from the tendency of most superconducting elements and compounds, primarily metals, to readily react with other elements, notably oxygen. He highlights miassite (Rh17S15) as a particularly intriguing mineral, citing its intricate chemical composition as one of its compelling features. “At first glance, you might assume that such a complex compound could only be synthetically created through targeted efforts, and not exist in nature,” Prozorov remarked. “However, as it turns out, miassite defies these expectations.”
Paul Canfield, Distinguished Professor of Physics and Astronomy at Iowa State University and a researcher at Ames Lab, brings his expertise in the design, discovery, growth, and characterization of novel crystalline materials to the forefront of this project. Canfield synthesized high-quality miassite crystals specifically for this endeavor. “While miassite was initially discovered near the Miass River in Chelyabinsk Oblast, Russia,” Canfield noted, “it remains a rarity, with well-formed crystals being exceptionally uncommon.”
Growing miassite crystals constituted a pivotal aspect of a broader initiative aimed at uncovering compounds that marry high-melting elements like Rhodium with volatile elements like Sulfur. Canfield elucidated on this endeavor, noting, “Contrary to the innate properties of these pure elements, our focus has been on harnessing mixtures that facilitate the low-temperature growth of crystals while minimizing vapor pressure.”
Describing the endeavor akin to stumbling upon a hidden fishing spot teeming with prized catches, Canfield highlighted the discovery of three new superconductors within the Rh-S system. Through meticulous measurements conducted by Ruslan’s team, miassite emerged as an unconventional superconductor.
Prozorov’s team, renowned for their expertise in employing advanced techniques to investigate superconductors at ultra-low temperatures, attested to the challenging conditions required for their experiments, necessitating temperatures as frigid as 50 millikelvins, equivalent to around -460°F.
Employing three distinct tests, the team scrutinized the nature of miassite’s superconductivity. Foremost among these was the “London penetration depth” test, which assesses the depth to which a weak magnetic field can penetrate the superconductor bulk from its surface. While conventional superconductors exhibit a relatively constant penetration depth at low temperatures, unconventional superconductors display a linear variation with temperature. Results confirmed miassite’s behavior as an unconventional superconductor.
Further experimentation involved inducing defects into the material—a signature technique refined by Prozorov’s team over the past decade. This involved bombarding the material with high-energy electrons to displace ions from their positions, thereby introducing defects in the crystal structure. While conventional superconductors remain largely unaffected by non-magnetic disorder, introducing defects alters or suppresses the critical temperature and magnetic field, characteristics crucial for unconventional superconductors. In miassite, the team observed expected changes in both critical temperature and magnetic field behavior, consistent with unconventional superconductors.
The exploration of unconventional superconductors not only enhances scientific comprehension but also holds significant implications for practical applications. Prozorov emphasized the importance of unraveling the mechanisms underlying unconventional superconductivity, citing its pivotal role in facilitating economically viable applications of superconductors.