Unconventional spin states in YPtBi

Physics 16, s93

Nuclear magnetic resonance spectroscopy offers strong evidence that YPtBi can exhibit topological superconductivity, a property that could be exploited to build quantum computers.

Y. Zhou and R. Zhou/Institute of Physics, Chinese Academy of Sciences

Existing quantum computers are prone to errors because they store information in superpositions of quantum states that can easily be destroyed. Researchers are developing an alternative technology that stores quantum information more robustly as Majorana fermions, quasiparticles that can be hosted by a class of materials known as topological superconductors. In a new experiment, Rui Zhou of the Physics Institute of the Chinese Academy of Sciences and colleagues investigated the superconducting properties of a candidate topological superconductor, yttrium platinum bismuth (YPtBi) [1].

Several key properties of YPtBi, including strong spin-orbit coupling and a lack of inversion symmetry, allow the material to sustain topologically non-trivial states. But whether such states include topological superconductivity depends on how the material’s electrons combine to form so-called Cooper pairs, the quasiparticles that carry supercurrents. Determining the type of coupling underlying the superconductivity in YPtBi has been difficult due to the material’s low charge carrier density and its low superconducting critical temperature.

Zhou and colleagues studied YPtBi at temperatures approaching absolute zero using nuclear magnetic resonance (NMR) spectroscopy. They placed a sample in a magnetic field to align the nuclear spins of a specific isotope, Pt-195. Then, by measuring how these nuclei returned to alignment after being perturbed by a radio-frequency pulse, they gleaned information about the electronic environment of the nuclei. The dependence of the relaxation rate and NMR spectra on the sample temperature suggested that, in the superconducting YPtBi, the Cooper pairs have more varied spin states than the spin-up and spin-down electron pairs alone of conventional superconductors.

Such unconventional coupling strengthens the hypothesis that YPtBi is a topological superconductor. The results will also inform models of the coupling mechanism in topological superconductors, improving the prospects of these materials in topological quantum computing.

Sophia Chen

Sophia Chen is a freelance science writer based in Columbus, Ohio.

References

  1. YZZhou et al.Antiferromagnetic spin fluctuations and unconventional superconductivity in the topological candidate superconductor YPtBi revealed by 195Pt-NMR, Phys. Rev. Lett. 130266002 (2023).

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