Uranium hydride tests find no predicted superconducting transition
Experiments on uranium and hydrogen compounds found metallic behaviour without the superconducting transitions anticipated by earlier calculations. Researchers tracked structural changes under extreme pressure and recovered one compound at ordinary conditions. The peer-reviewed early article version leaves a mismatch between theory and measurement, with magnetism among the factors under examination in the tested materials.
Science··Midday
The compounds remained metallic during cooling
High-pressure experiments on uranium hydrides, compounds combining uranium with hydrogen, found no superconducting transition in the measured temperature ranges. Electrical resistance indicated metallic behaviour. Several tested structures reached 3 kelvin without the transition anticipated in earlier theoretical work. The peer-reviewed early article version also reports an absent transition in another structure tested over a different, more limited cooling range.[1]
Changing pressure rearranged the crystal structures
The team followed a sequence of structural changes at pressures approaching 99 gigapascals. Samples compressed between diamond anvils and heated by laser formed different crystalline arrangements. Further transformations accompanied the release of pressure, eventually yielding a compound recoverable at ordinary pressure and temperature. It persisted as the main phase during hours of air exposure while slowly oxidising, establishing laboratory recovery of a high-pressure product.[1]
Hydrogen positions remain indirectly assigned
X-ray diffraction chiefly resolved the arrangement of heavy uranium atoms. The much weaker signal from hydrogen required its positions to be assessed using earlier experiments and calculations. Magnetic ordering is among the proposed influences on the unexpected electrical results. Additional theoretical explanation is still needed for the missing transitions. The findings concern the uranium compounds and conditions tested, with no general exclusion of superconductivity across other hydrides.[1]
