Chinese Researchers Discover Room-Temperature Superconductivity

Researchers in China have made a groundbreaking advancement in superconductivity by identifying a potential room-temperature superconductor. The team, led by physicist Yanming Ma from Jilin University, successfully compressed an alloy of lanthanum-scandium (La-Sc) and ammonia borane (NH3BH3) under extreme pressures ranging from 250 to 260 GPa. This experimentation resulted in the observation of superconductivity with a maximum onset temperature reaching 298 K, marking a significant milestone in the field.

Superconductors are materials that can conduct electricity without resistance, typically requiring extremely low temperatures to activate this property. Historically, the first superconductor, solid mercury, exhibited a critical temperature (Tc) of just 4.2 K. The pursuit of superconductors that operate at higher temperatures has been a focus of research for decades. Materials functioning at or near room temperature could revolutionize various technologies, including electric generators and magnetic resonance imaging (MRI) systems, by enabling lossless electricity transmission.

In the late 20th century, researchers made substantial progress with the discovery of high-temperature superconductors, particularly copper oxide superconductors, which had Tc values between 30 and 133 K. The breakthrough continued in 2015 with the discovery of a sulphide material, H3S, which achieved a Tc of 203 K under 150 GPa. A further advancement occurred in 2019 when lanthanum decahydride (LaH10) was found to have a Tc of 250–260 K under similar extreme pressures.

Ternary Hydrides: A New Frontier

The recent focus of superconductivity research has shifted towards ternary hydrides, which consist of three different atomic species. These materials are structurally complex and have the potential to exhibit higher Tc values. For instance, Li2MgH16 has been theoretically predicted to demonstrate superconductivity at temperatures between 351 and 473 K under multimegabar pressures. Other high-Tc hydrides, such as MBxHy and Mg2IrH6-7, are also thought to be stable at comparatively lower pressures.

In this latest study, Ma and his team investigated the compound LaSc2H24, formed by introducing scandium into the established La-H binary system. Utilizing a crystal structure prediction method known as CALYPSO, the researchers theorized that this ternary compound would exhibit a hexagonal P6/mmm symmetry. The introduction of scandium led to the formation of novel interlinked hydrogen clathrate “cages,” which are crucial for fostering superconductivity.

Through a series of experiments, the researchers placed LaSc2H24 in a diamond-anvil cell, a device capable of generating extreme pressures by compressing the sample between two diamond crystals while applying heat with a laser. In situ X-ray diffraction experiments confirmed that the material crystallized into the predicted hexagonal structure.

According to co-author Guangtao Liu, one of the critical indicators of superconductivity in the La-Sc-H ternary system was the consistent observation of zero electrical resistance below the Tc. Another significant finding was the reduction in Tc when an external magnetic field was applied, in line with conventional superconductivity theory, which states that magnetic fields can disrupt Cooper pairs—the charge carriers responsible for superconductivity.

Challenges and Future Directions

The path to this discovery was fraught with challenges. Liu noted that the first six months of attempting to synthesize LaSc2H24 at pressures below 200 GPa did not yield any significant enhancements in Tc. The researchers eventually had to increase the pressure beyond 250 GPa, manually layering three precursor materials and ensuring proper electrical connections within a minuscule sample chamber, measuring just 10 to 15 μm across.

The successful synthesis of LaSc2H24 involved meticulous preparation of precursor alloys, as the differing atomic radii of scandium and lanthanum made it difficult to achieve the desired molar ratios through conventional melting methods. After extensive experimentation, the team adopted a magnetron sputtering technique to produce films with the correct proportions.

Sven Friedemann from the University of Bristol, who did not participate in the study, remarked that this research represents a significant advancement in superconductivity, especially with the new record transition temperature of 295 K. He emphasized the importance of further investigations to confirm the superconductivity claims and explore additional characteristics of the material.

Moving forward, Ma and his colleagues plan to continue investigating the properties of LaSc2H24, aiming to verify the isotope effect—an important hallmark of conventional superconductors—and to measure the superconducting critical current. The team also intends to directly detect the Meissner effect, a key characteristic of superconductivity, while exploring new multinary superhydrides to achieve superior superconducting properties at lower pressures.

The findings from this research have been made available on the arXiv pre-print server, paving the way for future exploration in the promising field of superconductivity.