Cooling This Uranium Crystal Makes One Kind of Superconductivity Vanish

Physicists have measured a transition in which uranium ditelluride loses one of its two kinds of superconductivity as it gets colder, the reverse of the usual direction. Sahas Kamat, Brad Ramshaw and colleagues report the measurement in Nature Physics, published Oct. 30, 2026.

The published map of the material under pressure had a problem. That map, the phase diagram, charts where each kind of superconductivity appears as temperature, pressure and magnetic field change, and the one in the literature showed two boundaries crossing in a way thermodynamics does not allow. The authors report that the boundary they found resolves it and establishes a tetracritical point, a place where four phases meet, past which the material's two superconducting states combine into one.

The team used pulse ultrasound, sound pulses timed through the crystal, and found an upward jump in the speed of sound at the new boundary. The paper calls that "direct thermodynamic evidence for a phase transition in which superconducting order is lost on cooling." Cornell University's release describes the squeeze as about 18,000 pounds focused on five millimeters, "like nine cars balanced on your pinky," Kamat said; the pressure was locked in at room temperature before the crystal was cooled to between 2 and 1 kelvin.

In this material, one kind of superconductivity appears on cooling alone, and a second only under strong magnetic fields or pressure. The authors report that competition between the two drives the loss of order on cooling and locks the two states together, damping fluctuations in their superconductivity.

"No one has yet convincingly demonstrated a topological superconductor, but now we know that uranium ditelluride at least has the right ingredients to make it happen," said Brad Ramshaw, the Cornell physicist who is the paper's corresponding author. The paper still calls the material a candidate, and Ramshaw said any application in quantum computing is several steps away.

Co-authors are from the University of Maryland, the Karlsruhe Institute of Technology and the Canadian Institute for Advanced Research, according to the release. The paper says the measured data are freely available on GitHub.