Chinese Researchers Discover Room-Temperature Superconductor at 260 GPa

Researchers at Jilin University in China have made a groundbreaking discovery by identifying a potential room-temperature superconductor. By compressing a lanthanum-scandium (La-Sc) alloy combined with ammonia borane (NH3BH3) at pressures between 250–260 GPa, they observed superconductivity with a maximum onset temperature of 298 K, a significant achievement in the field of superconductivity.

Superconductors are materials that can conduct electricity without resistance, typically requiring extremely low temperatures to function. The first superconductor, solid mercury, has a transition temperature (Tc) of just 4.2 K. Most researchers have focused on finding materials that can operate at higher temperatures to improve efficiency in various applications, including power transmission and magnetic resonance imaging (MRI).

Progress in this area surged during the late 20th century with the discovery of high-temperature superconductors, particularly copper oxides, which have Tc values ranging from 30 K to 133 K. In 2015, the record was further elevated with the identification of a sulphide material, H3S, which exhibited a Tc of 203 K under pressure. This paved the way for ongoing research into hydrogen-rich materials, which have shown promise in achieving higher superconducting temperatures.

Advancements in Ternary Hydrides

In recent years, the focus has shifted toward ternary hydrides—complex compounds composed of three different atomic species. These materials demonstrate a greater structural complexity than binary hydrides, potentially leading to higher Tc values. For instance, Li2MgH16 has been predicted to achieve hot superconductivity with a Tc ranging from 351 K to 473 K under extreme pressures. Other high-Tc hydrides like MBxHy and Mg2IrH6-7 are also noted for their stability under comparatively lower pressures.

The research team, led by physicist Yanming Ma, specifically investigated LaSc2H24, a compound formed by doping scandium into the established lanthanum-hydrogen binary system. Using the crystal structure prediction method known as CALYPSO, the researchers anticipated that LaSc2H24 would adopt a hexagonal P6/mmm symmetry. This configuration includes two unique hydrogen clathrate “cages” surrounding the scandium and lanthanum atoms, which are essential for achieving high-temperature superconductivity.

To experimentally validate their predictions, the team utilized a diamond-anvil cell to generate the necessary extreme pressures while heating the sample. X-ray diffraction measurements confirmed that the compound crystallized into the anticipated hexagonal structure, aligning with the predicted LaSc2H24 configuration.

Experimental Challenges and Future Directions

Co-author Guangtao Liu highlighted the significance of their findings, noting that multiple measurements indicated the onset of zero electrical resistance below the Tc. Additionally, they observed a consistent decrease in Tc when an external magnetic field was applied, aligning with conventional superconductivity theories.

The path to this discovery was fraught with challenges. Liu recounted that initial attempts to synthesize LaSc2H24 at pressures below 200 GPa yielded no significant enhancement in Tc. The team eventually had to increase the pressure above 250 GPa, requiring meticulous preparation of precursor layers and precise electrode connections in a diminutive sample chamber measuring only 10 to 15 μm in size.

After extensive experimentation, the researchers successfully synthesized LaSc2H24 using magnetron sputtering to control the molar ratios of scandium and lanthanum, a task complicated by their differing atomic radii. Liu noted that their efforts resulted in approximately 70 pairs of diamonds being damaged during the process.

Sven Friedemann from the University of Bristol, who was not involved in the research, remarked that this study represents a significant advancement in superconductivity, highlighting the new record transition temperature of 295 K. He expressed enthusiasm for future investigations into superconductivity signatures, emphasizing the need for comprehensive X-ray diffraction measurements to confirm the structural claims.

Ma and his team plan to further explore the properties of LaSc2H24, including verifying the isotope effect and measuring superconducting critical currents. They aim to directly detect the Meissner effect, a hallmark of superconductors, and are also looking to synthesize additional multinary superhydrides to enhance superconducting properties at lower pressures.

The full study is available on the arXiv pre-print server, indicating a promising avenue for future research in the quest for room-temperature superconductivity.