Topological Surface State Visualization in Spin-Triplet Superconductor UTe2

Although UTe₂ appears to be the first 3D spin-triplet topological superconductor, its superconductive order-parameter has not yet been established. If spin-triplet, it should have odd parity so that  and, in addition, may break time-reversal symmetry. A distinctive identifier of  3D spin-triplet topological superconductors is the appearance of an Andreev bound state (ABS) on all surfaces parallel to a nodal axis, due to the presence of a topological surface band (TSB). Moreover, theory shows that specific ABS characteristics observable in tunneling to an s-wave superconductor distinguish between chiral and non-chiral . To search for such phenomena in UTe₂ we employ s-wave superconductive scan-tip imaging of UTe₂[1] to discover a powerful zero-energy ABS signature at the (0-11) crystal termination[2]. Its imaging yields quasiparticle scattering interference signatures of two  nodes aligned with the crystal a-axis. Most critically, development of the zero-energy Andreev conductance peak into two finite-energy particle-hole symmetric conductance maxima as the tunnel barrier is reduced, signifies that UTe₂ superconductivity is non-chiral. Overall, the discovery of a TSB, of its a zero-energy ABS, of internodal scattering along the a-axis, and of splitting the zero-energy Andreev conductance maximum due to s-wave proximity, categorizes the superconductive as the odd-parity non-chiral B_3u state[2].

[1] Nature, 618, 921–927 (2023) 

[3] Gu, Wang, et al. Science (2023)