QPI Imaging of Subgap Quasiparticles in the Superconducting Topological Surface State of UTe₂

UTe₂ has emerged as a leading candidate for exhibiting odd-parity superconductivity, where the 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 odd-parity 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 q_i (i=1-6). Theoretical analysis indicates that these patterns are most consistent with a bulk Δ(k) of time-reversal-invariant odd-parity B_3u symmetry.