Researchers from Cornell University have discovered a new phase of matter in potential topological superconductors that could have a significant impact on spintronics, quantum computing, and condensed matter physics.
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The Macroscopic Quantum Matter Group at Cornell University has used one of the most potent millikelvin Scanned Josephson Tunnelling Microscopes (SJTM) in the world to find and observe a crystalline yet superconducting state in the novel and unique superconductor uranium ditelluride (UTe2).
This “spin-triplet electron-pair crystal” is a topological quantum state that has never been observed before.
The study, “Detection of a Pair Density Wave State in UTe2,” was published in Nature on 28th June 2023.
The study was co-led by Qiangqiang Gu, a postdoctoral researcher working in the laboratory of physicist J.C. Séamus Davis, the James Gilbert White Distinguished Professor Emeritus in the College of Arts and Sciences. Joe Carroll of University College Cork and Shuqiu Wang of Oxford University also contributed to the study.
When the pairing potential exhibits odd parity, each electron pair adopts a spin-triplet state with both electron spins pointing in the same direction, resulting in superconductors.
Since they could theoretically serve as the foundation for ultra-stable quantum computers, topological superconductors are the subject of significant investigation by physicists, according to Gu.
Except superfluid 3He, which was also discovered at Cornell, no bulk materials have, despite a decade of intense research into topological superconductivity, been categorically acknowledged as spin-triplet, odd-parity superconductors.
Uranium Ditelluride (UTe2), a relatively new material, has emerged as a highly attractive contender for this categorization. According to Gu, the superconductive order parameter remains elusive.
Theoretical physicists began to postulate in 2021 that UTe2 is actually in a topological pair-density-wave (PDW) state. No such quantum matter had ever been discovered.
A PDW is analogous to the stationary dance of paired electrons in a superconductor, except the pairs produce periodic crystalline patterns in space.
Our team at Cornell discovered the first PDW ever observed in 2016 using the superconductive-tip Scanned Josephson Tunnelling Microscope that we invented for that purpose. Since then, we have pioneered SJTM studies at millikelvin temperatures and with microvolt energy resolution.
Qiangqiang Gu, Postdoctoral Researcher, Cornell University
Gu added, “For the UTe2 project, we have directly visualized the spatial modulations of the superconducting pairing potential at atomic scale and found them to modulate exactly as predicted in a PDW state as the density of electron pairs modulates periodically in space. What we detected is a new quantum matter state—a topological pair density wave composed of spin-triplet Cooper pairs.”
Cooper-pair density waves are a type of electronic quantum matter in which pairs of electrons create a superconductive PDW state rather than the more typical “superconductive” fluid in which they are all in the same state of free motion.
Gu added, “The discovery of the first PDW in spin-triplet superconductors is exciting. Uranium-based heavy fermion superconducting compounds are a new and exotic class of materials that provide a promising platform for realization of topological superconductivity.”
Gu concluded, “Our scientific discovery also points out the ubiquitous nature of this intriguing quantum state in s-wave, d-wave, and p-wave superconductors, and it sheds light on new avenues for identifying such states in a broad spectrum of materials.”
Gu, Q., et al. (2023) Detection of a pair density wave state in UTe2. Nature. doi:10.1038/s41586-023-05919-7.