Detection of a pair density wave state in UTe2


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Published Article Nature 618, 921 - June 2023

The properties of superconducting materials, their perfectly dissipationless electronics, perfect diamagnetism, and macroscopic quantum mechanical dynamics are all the products of the formation of a macroscopic quantum fluid of electron pairs. To better understand this, we have developed the first scanned Josephson/Andreev tunneling microscopes (SJTM/SATM) which provide direct access to the macroscopic quantum electron pair condensate.

Since the 1960s the possibility of a crystalline superconducting phase within the overall fluid has been discussed with great interest in the superconducting community. Such a state should manifest itself as a spatially periodic electron-pair crystal; we call this state a Pair Density Wave (PDW). For years the superconducting community had suggested that such a PDW state might exist in the high-temperature superconductor Bi2Sr2CaCu2O8+x. In 2016 our group developed our first SJTM system and subsequently detected this long predicted PDW state. Since then we have discovered PDWs in several other materials including in the transition metal dichalcogenide superconductor NbSe2.

Recently our focus of study has been the spin-triplet topological superconductor UTe2. This class of superconductor should exhibit many unprecedented electronic properties including fractionalized electronic states relevant to quantum information processing. In UTe2 we searched for a PDW state, by visualizing the pairing energy-gap with µeV-scale energy-resolution made possible by a superconducting SATM tip. We discovered three PDWs at incommensurate wavevectors Pi=1,2,3 that are indistinguishable from the wavevectors Qi=1,2,3 of the prevenient CDW. From these observations and given UTe2 as a spin-triplet superconductor, this PDW state appears to be the first known spin-triplet pair density wave.

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