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, its superconductive order-parameter ∆k  remains unknown. Many diverse forms for ∆k  are physically possible in such heavy fermion materials. Moreover, intertwined density waves of spin (SDW), charge (CDW) and pairs (PDW) may interpose, with the latter exhibiting spatially modulating superconductive order-parameter ∆r , electron pair density and pairing energy-gap. Hence, the newly discovered CDW state in UTe₂ motivates the prospect that a PDW state may exist in this material. To search for it, we visualize the pairing energy-gap with μeV–scale  energy-resolution using superconductive STM tips. We detect three PDWs, each with peak-peak gap modulations circa 10 μeV  and at incommensurate wavevectors Pi=1,2,3  that are indistinguishable from the wavevectors Qi=1,2,3  of the prevenient CDW. Concurrent visualization of the UTe₂ superconductive PDWs and the non-superconductive CDWs reveals that every Pi:Qi  pair exhibits a relative spatial phase δϕ≈π.  From these observations and given UTe₂ as a spin-triplet superconductor_,this PDW state should be a spin-triplet pair density wave. While such states do exist in superfluid ³He, for superconductors they are unprecedented.

Read more about our research → Nature 618, 921–927 (2023)