An international research team has provided the first definitive proof of superconductivity in a high-pressure form of lanthanum nickelate, a material that has intrigued physicists for its potential to conduct electricity with zero resistance at relatively high temperatures. The scientists successfully observed the Meissner effect, the complete expulsion of a magnetic field, which is a fundamental and required characteristic of a true superconductor. This confirmation overcomes significant technical hurdles that had previously left the material’s superconducting nature in question.
The finding is a crucial step forward in the study of nickel-based superconductors, which are considered potential analogs to the Nobel-winning copper-based cuprates that exhibit superconductivity at high temperatures. By confirming that the lanthanum nickelate La₃Ni₂O₇ is a genuine high-temperature superconductor, this work opens a new frontier for exploring unconventional superconductivity. The novel techniques developed to perform the measurements under extreme pressure also establish a new standard for validating superconductors in challenging experimental conditions, potentially accelerating the discovery of materials that could one day function near room temperature and revolutionize energy transmission and computing.
A Gold Standard of Confirmation
In the world of physics, two critical benchmarks must be met to declare a material a superconductor. The first, and most widely known, is zero electrical resistance. This allows a current to flow indefinitely without energy loss. While the nickelate material in question, La₃Ni₂O₇, had shown evidence of zero resistance in initial 2023 experiments at temperatures around 80 Kelvin (–193° Celsius), this property alone is not sufficient proof. Certain other physical phenomena can mimic zero resistance, making a second, more rigorous test necessary.
That second test is the observation of the Meissner effect, a definitive signature of the superconducting state. When a material transitions into a superconductor, it actively expels all magnetic fields from its interior. This diamagnetism is a unique and unambiguous property. The research team, led by Prof. Liu Xiaodi of the Hefei Institute of Physical Science at the Chinese Academy of Sciences, in collaboration with Jilin University and Sun Yat-sen University, focused on detecting this elusive effect. Its confirmation provides the ironclad evidence that had been missing from the scientific community, solidifying the material’s status and justifying the excitement surrounding its discovery. The results were formally published in the peer-reviewed journal Physical Review Letters.
Advanced Sensors in Extreme Environments
Observing the Meissner effect in this nickelate was a monumental technical challenge due to the extreme conditions required to make it superconduct. The material only enters its superconducting state when subjected to immense pressures, typically between 22 and 28 gigapascals (GPa), which is more than 200,000 times the atmospheric pressure at sea level. These conditions are created within a diamond anvil cell, a device that compresses a tiny sample between the tips of two diamonds.
A Novel Measurement Technique
Traditional magnetic sensors are difficult to integrate into the microscopic space of a diamond anvil cell and often lack the sensitivity to detect the faint magnetic signal from a tiny, potentially inhomogeneous sample. To overcome this, the researchers employed a cutting-edge technique known as diamond nitrogen-vacancy (NV) center quantum sensing. This method uses atomic-scale defects within the diamond anvil itself as ultra-precise magnetic field detectors. These NV centers act like tiny quantum compasses, allowing the team to map the magnetic field at the micron scale directly on the surface of the sample crystal.
Synchronized Evidence
By combining the NV center magnetometry with simultaneous four-probe electrical resistance measurements on the exact same crystal, the team could directly correlate the disappearance of resistance with the expulsion of the magnetic field. This synchronized approach provided airtight evidence, showing that the regions exhibiting zero resistance were the same ones pushing out the magnetic field. This dual-pronged verification eliminated any ambiguity and confirmed that the superconductivity was a bulk property of the material, not just a surface effect or an experimental artifact.
Understanding the Nickelate Family
The discovery of high-temperature superconductivity in copper-based oxides, or cuprates, in the 1980s earned a Nobel Prize and sparked a revolution in materials science. For decades, scientists have theorized that nickel-based compounds, or nickelates, could share similar properties because nickel sits next to copper on the periodic table and possesses a similar electronic structure. This confirmation of robust superconductivity in La₃Ni₂O₇ provides the strongest validation yet of that long-held hypothesis.
However, nickelates are not perfect analogs to cuprates, and their differences are just as important. The crystal structure and electronic behavior of this high-pressure lanthanum nickelate introduce new variables for physicists to study. For example, the researchers noted that the superconducting transition temperature varied with pressure, peaking around 76 K at 22 GPa and decreasing slightly at higher pressures. Understanding the mechanisms behind this pressure dependence is a key question that will drive future theoretical and experimental work. This research solidifies nickelates as a vital new family of materials for studying, and ultimately understanding, the mysterious physics behind high-temperature superconductivity.
Implications for Future Discoveries
While a material requiring tens of gigapascals of pressure is not practical for everyday applications like power lines or magnetic levitation trains, its discovery has profound implications for the broader search for a room-temperature superconductor. This work demonstrates that high-temperature superconductivity can be found in new families of materials beyond the well-trodden cuprates. It energizes the field by providing a new chemical playground for scientists to explore, tune, and theorize about. The insights gained from studying the electronic and structural properties of this nickelate under pressure will inform the design of new materials that might exhibit similar properties under more manageable conditions.
Furthermore, the experimental success of using NV center quantum sensing to validate a superconductor under extreme pressure is a significant advancement in its own right. This technique provides a powerful new tool for researchers investigating quantum materials in previously inaccessible environments. As scientists continue to explore materials that only reveal their most exotic properties under immense pressures or intense magnetic fields, this sensing technology will be critical. It lowers the barrier to confirming new discoveries, reducing the ambiguity that can sometimes linger for years around preliminary reports of superconductivity. This accelerates the cycle of discovery, allowing the scientific community to focus its efforts on the most promising candidates in the ongoing quest for the ultimate prize in materials science.