Detection of a pair density wave state in UTe(2)

Spin-triplet topological superconductors should exhibit many unprecedented electronic properties, including fractionalized electronic states relevant to quantum information processing. Although UTe(2) may embody such bulk topological superconductivity(1–11), its superconductive order parameter Δ(k) remains unknown(12). Many diverse forms for Δ(k) are physically possible(12) in such heavy fermion materials(13). Moreover, intertwined(14,15) density waves of spin (SDW), charge (CDW) and pair (PDW) may interpose, with the latter exhibiting spatially modulating(14,15) superconductive order parameter Δ(r), electron-pair density(16–19) and pairing energy gap(17,20–23). Hence, the newly discovered CDW state(24) in UTe(2) motivates the prospect that a PDW state may exist in this material(24,25). To search for it, we visualize the pairing energy gap with μeV-scale energy resolution using superconductive scanning tunnelling microscopy (STM) tips(26–31). We detect three PDWs, each with peak-to-peak gap modulations of around 10 μeV and at incommensurate wavevectors P(i=1,2,3) that are indistinguishable from the wavevectors Q(i=1,2,3) of the prevenient(24) CDW. Concurrent visualization of the UTe(2) superconductive PDWs and the non-superconductive CDWs shows that every P(i):Q(i) pair exhibits a relative spatial phase δϕ ≈ π. From these observations, and given UTe(2) as a spin-triplet superconductor(12), this PDW state should be a spin-triplet PDW(24,25). Although such states do exist(32) in superfluid (3)He, for superconductors, they are unprecedented.