Superconductivity: ultrasound sheds light on the states of UTe2
· BehindLines newsroom
Can one material host several forms of superconductivity at the same time? A team led at Cornell is providing new evidence in the case of uranium ditelluride, UTe2. On 30 October the university presented experiments that clarify the conditions under which two states coexist. They strengthen a line of research, but they do not establish the existence of the topological superconductor that is hoped for in quantum computing.
The issue concerns the phase diagram: a map showing the states of the material as a function of temperature, pressure and magnetic field. In their preprint, the researchers explain that an apparent meeting of certain boundaries on this map raised a thermodynamic problem, because it should not be possible. Previously published maps therefore seemed to them inconsistent with thermodynamics.
To see more clearly, they sent ultrasound pulses through the material. A particular jump in the speed of sound reveals a new boundary between the phases. Their analysis brings out a point where four regions meet, known as a tetracritical point, and beyond it a state combining several superconducting components.
The behaviour also has a peculiar feature: on further cooling, one superconducting order can disappear. The team attributes this to competition between the two components, one pushing the other out. Cooling further therefore does not necessarily strengthen every form of superconductivity present in this material.
Cornell places the experiments at very low temperature, between one and two kelvin (roughly −272 °C), under high pressure. The work remains fundamental research: it describes neither a working computing component nor an application at room temperature. The university's communication and the preprint come from the same team and concern the same study, so they are not two independent replications. The preprint was submitted in March and revised in July; Cornell announces its publication in Nature Physics on 30 October.