Detection of a pair density wave state in UTe₂

Spin-triplet topological superconductors should exhibit many unprecedented electronic properties, including fractionalized electronic states relevant to quantum information processing. Although UTe2 may embody such bulk topological superconductivity(1-11), its superconductive order parameter Delta(k) remains unknown(12). Many diverse forms for Delta(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 Delta(r), electron-pair density(16-19) and pairing energy gap(17,20-23). Hence, the newly discovered CDW state(24) in UTe2 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 mu eV-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 mu eV and at incommensurate wavevectors P-i=1,P-2,P-3 that are indistinguishable from the wavevectors Q(i=1,2,3) of the prevenient(24) CDW. Concurrent visualization of the UTe2 superconductive PDWs and the non-superconductive CDWs shows that every P-i:Q(i) pair exhibits a relative spatial phase delta phi approximate to pi. From these observations, and given UTe2 as a spin-triplet superconductor(12), this PDW state should be a spin-triplet PDW24,25. Although such states do exist(32) in superfluid He-3, for superconductors, they are unprecedented.