μ⁺ Knight shift studies of UTe₂

Recently discovered UTe₂ is believed to be a rare example of an unconventional odd-parity superconductor. Electronic specific heat and electrical resistivity measurements [1], as well as nuclear magnetic resonance (NMR) measurements [2], indicate the superconducting state of UTe₂ emerges from a well-developed heavy Fermi liquid. However, by way of muon (μ⁺) Knight shift measurements on UTe₂ single crystals grown via a chemical vapor transport (CVT) method, we have found evidence for a significant re-localization of uranium 5f electrons prior to the onset of superconductivity [3]. The coexistence of localized moments and a Fermi liquid in the normal state of UTe₂ is surprising and may be a consequence of an under-screened Kondo lattice. We also observe an unusual component of the muon Knight shift, which despite the c-axis alignment of the external magnetic field, scales with the a-axis bulk magnetic susceptibility above T ∼12 K. These results will be discussed along with findings from a similar muon Knight shift study we have recently carried out on higher quality UTe₂ single crystals grown by a molten salt-flux (MSF) method.



References

[1] S. Ran et al., Science 365, 684 (2019).

[2] K. Kinjo et al., Phys. Rev. B 105, L140502 (2022).

[3] N. Azari et al. Phys. Rev. B 108, L081103 (2023).