Possible Coexistence of Antiferromagnetic and Ferromagnetic Spin Fluctuations in the Spin-triplet Superconductor UTe2 Revealed by 125Te NMR under Pressure

A spin-triplet superconducting state mediated by ferromagnetic (FM) spin fluctuations has been suggested to occur in the newly discovered heavy-fermion superconductor UTe${}_2$. However, the recent neutron scattering measurements revealed the presence of antiferromagnetic (AFM) spin fluctuations in UTe${}_2$. Here, we report the ${}^{125}$Te nuclear magnetic resonance (NMR) studies of a single-crystal UTe${}_2$, suggesting the coexistence of FM and AFM spin fluctuations in UTe${}_2$. Owing to the two different Te sites in the compound, we conclude that the FM spin fluctuations are dominant within ladders and the AFM spin fluctuations originate from the inter-ladder magnetic coupling. Although AFM spin fluctuations exist in the system, the FM spin fluctuations in the ladders may play an important role in the appearance of the spin-triplet superconducting state of UTe${}_2$.