Kuanysh Zhussupbekov (Cornell University and University College Cork) - QPI Imaging of Subgap Quasiparticles in the Superconducting Topological Surface State of UTe₂

Abstract:

UTe_₂ has emerged as a leading candidate for exhibiting intrinsic topological superconductivity, where the bulk pairing potential Δ(k) satisfies Δ(-k) = -Δ(k). While no material has definitively shown this behavior, Bogoliubov quasiparticle interference (QPI) imaging is a promising technique for determining Δ(k) in complex superconductors. In intrinsic topological superconductors, a unique Bogoliubov quasiparticle surface band (QSB) is expected to form within the energy gap |E| ≤ Δ which, for typical Fermi surface geometries is also a superconductive topological surface state. Hence, in theory, QPI should be dominated by the QSB's electronic structure k(E) while also reflecting the bulk pairing symmetry Δ(k). Using a superconducting scan-tip to enhance QPI sensitivity in UTe₂, we observe distinct in-gap quasiparticle interference patterns on the (0-11) surface, characterized by six modulation vectors qi (i=1-6). Theoretical analysis indicates that these patterns are most consistent with a bulk Δ(k) of time-reversal-invariant odd-parity B3u symmetry.

* S. Wang, K. Zhussupbekov, J.P. Carroll, et al., Imaging Odd-Parity Quasiparticle Interference in the Superconductive Surface State of UTe2, Nature Physics - under review.

* Q. Gu, S. Wang, J.P. Carroll, K. Zhussupbekov, et al., Pair Wavefunction Symmetry in UTe2 from Zero-Energy Surface State Visualization, arXiv. 2501.16636 (2025).