Low-Temperature Magnetic Fluctuations Investigated by <sup>125</sup>Te-NMR on the Uranium-Based Superconductor UTe<sub>2</sub>
Hiroki Fujibayashi, Katsuki Kinjo, Genki Nakamine, Shunsaku Kitagawa, K. Ishida, Y. Tokunaga, H. Sakai, S. Kambe, Ai Nakamura, Yusei Shimizu, Yoshiya Homma, Dexin Li, Fuminori Honda, Dai Aoki
Abstract
To investigate the static and dynamic magnetic properties on the uranium-based superconductor UTe$_{2}$, we measured the NMR Knight shift $K$ and the nuclear spin-lattice relaxation rate $1/T_{1}$ in $H \parallel a$ by $^{125}$Te-NMR on a $^{125}$Te-enriched single-crystal sample. $1/T_1T$ in $H \parallel a$ is much smaller than $1/T_1T$ in $H \parallel b$ and $c$, and magnetic fluctuations along each axis are derived from the $1/T_1T$ 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 UTe$_2$ 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.