𝑏-axis and 𝑐-axis Knight shift measurements in the superconducting state on ultraclean UTe₂ with 𝑇𝑐=2.1 K

Knight shifts along the 𝑏 and 𝑐 axes (𝐾𝑏 and 𝐾𝑐) at two crystallographically distinct Te sites were measured down to 70 mK using ¹²⁵Te nuclear magnetic resonance on an ultraclean UTe₂ single crystal with a superconducting (SC) transition temperature 𝑇𝑐=2.1 K. This was carried out to determine the 𝒅-vector components, which are the order parameter in the spin-triplet pairing. Although the decrease in 𝐾𝑏 and 𝐾𝑐 is comparable to the theoretical estimation of the SC diamagnetic shielding effect, it is confirmed, by taking the difference between two Knight shifts at the distinct Te sites, that the spin susceptibility along the 𝑏 and 𝑐 axes decreases in the SC state. Taking into account the large decrease in 𝐾𝑎 in the SC state, we conclude that the 𝒅 vector has components along all three crystal axes.