Intrinsic low-temperature magnetic properties on ultraclean UTe₂ with 𝑇𝑐=2.1 K revealed by ¹²⁵Te NMR

To investigate the intrinsic magnetic properties of UTe₂, we performed ¹²⁵Te-NMR measurements on the ultraclean single-crystalline UTe₂ with superconducting transition temperature 𝑇𝑐=2.1 K and compared the results with those of the 𝑇𝑐=1.6 K sample. The broadening of the linewidth of the NMR spectrum in the 𝑎-axis magnetic field and the low-temperature magnetic fluctuations observed in the 1.6 K sample are suppressed in the ultraclean sample, indicating that such magnetic properties originate from a tiny amount of U deficiency. The present results suggest that the magnetic properties in UTe₂ are sensitive to the U deficiency. We also observed a peculiar angular dependence of the NMR quantities due to large magnetic anisotropy with the 𝑎 axis as the magnetic easy axis.