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A Forked Path for Superconductivity

Research activity on uranium ditelluride (UTe2) has surged in the last year following the discovery that it realizes a unique superconducting state (“spin-triplet” superconductivity) that appears to be the first solid-state analogue of 3He superfluidity. This form of superconductivity is believed to give rise to exotic quasiparticle states that could, in theory, enable fault-tolerant quantum computing.

To explore the origins of this long-sought type of superconductivity, scientists at New York University and the Advanced Light Source (ALS), in close collaboration with groups at the University of Maryland and Rutgers University, used angle-resolved photoemission spectroscopy (ARPES) at ALS Beamline 4.0.3 to measure the low-energy states occupied by electrons in UTe2.

The microscopic electronic environment revealed by these measurements is extraordinarily unusual. Two principal types of conducting electronic states were found, running along atomic chains aligned with the x– and y-axes of the crystal. One-dimensional conducting channels are often found within fibrous crystals, but it is surprising—and almost paradoxical—to have such channels run in two orthogonal directions.

The investigation also revealed a third band of uranium electrons that are very slow moving and appear to travel more isotropically. Minimal models of triplet superconductivity tend to involve at least two electronic bands that can co-occupy the same atom, and the slow movers appear to combine with the x-oriented one-dimensional electrons to fulfill this key role.

The experimental map of these electron populations is vital to understanding and harnessing triplet superconductivity, as it constitutes the setting from which the unique superconducting state emerges.

Left: Ball-and-stick structure with red spheres (uranium), green spheres (telluride-1), and blue spheres (telluride-2). Right: Cube showing three different cuts through the ARPES data.
Left: Crystal structure of UTe2 showing two orthogonal 1D chains in the horizontal plane (red and blue arrows). Right: ARPES data of the UTe2 electronic band structure showing the two orthogonal 1D Fermi surface metallic band crossings that arise from U 6d electron-like and Te(2) 5p hole-like states.

L. Miao, S. Liu, Y. Xu, E.C. Kotta, C.-J. Kang, S. Ran, J. Paglione, G. Kotliar, N.P. Butch, J.D. Denlinger, and L.A. Wray, “Low energy band structure and symmetries of UTe2 from angle resolved photoemission spectroscopy,” Phys. Rev. Lett. 124, 076401 (2020), doi:10.1103/PhysRevLett.124.076401.