Lanthanum hydrides, including LaH₁₀, are among the superconducting systems with the highest known transition temperatures. They typically require extreme pressures above 100 GPa to remain stable. Their tiny sample size makes the Meissner effect difficult to study with conventional magnetic measurements.
A team from the Institute of Physics of the Chinese Academy of Sciences and the Beijing National Center for Condensed Matter Physics used a quantum sensor based on nitrogen-vacancy centres in diamond. By improving the pressure-transmitting medium, the researchers raised the sensor’s operating pressure to nearly 180 GPa.
In sufficiently annealed samples, zero-field cooling followed by warming in a magnetic field revealed local magnetic screening. Field-cooling and warming experiments also confirmed the spontaneous Meissner effect for magnetic flux.
At 155 GPa, the sample’s superconducting transition temperature reached 237 K, close to the 240–255 K record range reported for LaH₁₀. Less thoroughly annealed samples showed lower transition temperatures of 190–220 K. Synchrotron X-ray diffraction measurements indicated that the transition corresponded to the LaH₉.₅±δ phase.
Spatially resolved magnetic imaging also found superconducting and non-superconducting regions coexisting within the sample. The finding provides a quantitative basis for assessing and improving the uniformity of hydride samples.
The study provides direct experimental evidence of the Meissner effect in superconducting lanthanum hydrides and demonstrates the potential of diamond quantum sensors under extreme pressure. The results were published in the Proceedings of the National Academy of Sciences (PNAS). The work received support from China’s national research programmes and Chinese Academy of Sciences projects.
