Helium doesn’t play well with others. Beyond its noble gas designation on the periodic table, it has the lowest electron affinity—zero—among the elements, and the highest ionization energy. Scientists have managed to mechanically pack He atoms with other elements, but the He has little effect on those compounds’ characteristics.

Now an international team has presented evidence for a compound whose electronic structure and thus its physical properties are influenced by its He components. Researchers led by Artem Oganov ran a crystal structure prediction algorithm to play matchmaker for He and found that the compound Na2He should form at high pressures. The researchers shared their prediction with Alexander Goncharov and colleagues, who loaded He gas and solid sodium into a diamond-anvil cell at the Carnegie Institution for Science. After increasing the pressure to 140 GPa and heating the sample, Goncharov’s team noticed a marked shift in material properties. New...

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