Low-Temperature Magnetic Fluctuations Investigated by 125Te-NMR on the Uranium-Based Superconductor UTe2.

To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe₂, we measured the NMR Knight shift K and the nuclear spin–lattice relaxation rate 1/T₁ in H || a by ¹²⁵Te-NMR on a ¹²⁵Te-enriched single-crystal sample. 1/T₁T in H || a is much smaller than 1/T₁T in H || b and c, and magnetic fluctuations along each axis are derived from the 1/T₁T measured in H parallel to all three crystalline axes. The magnetic fluctuations are almost identical at two Te sites and isotropic at high temperatures, but become anisotropic below 40 K, where heavy-fermion state is formed. The character of magnetic fluctuations in UTe₂ is discussed with the comparison to its static susceptibility and the results on other U-based superconductors. It is considered that the magnetic fluctuations probed with the NMR measurements are determined by the magnetic properties inside the two-leg ladder formed by U atoms, which are dominated by the q_a = 0 ferromagnetic fluctuations. [ABSTRACT FROM AUTHOR]