What it is
Lanthanum hydride shows signatures of superconductivity at around 250 K, but verifying its Meissner effect is hard because it requires megabar pressures. Using a gaseous pressure-transmitting medium, the authors extended the working pressure of nitrogen-vacancy centers in diamond to nearly 180 GPa, then used them as a quantum probe to observe magnetic-field screening and the Meissner effect of lanthanum hydride at around 240 K and 155 GPa, consistent with the record transition temperature of LaH10. Spatially resolved measurements also revealed significant inhomogeneities in an insufficiently annealed sample with a lower transition temperature of approximately 220 K.
Why it matters
Claims of high-temperature superconductivity in hydrides have been difficult to settle largely because the defining Meissner effect is so hard to confirm at the megabar pressures involved. Directly imaging magnetic-field screening at around 240 K with a diamond quantum sensor provides experimental evidence for superconductivity in lanthanum hydride and shows that spatially resolved probes can characterize and optimize samples under ultrahigh pressure.
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Filed underHigh-pressure geophysics and materials, Diamond and Carbon-based Materials Research, Rare-earth and actinide compounds