Possible coexistence of antiferromagnetic and ferromagnetic spin fluctuations in the spin-triplet superconductor UTe2 revealed by Te125 NMR under pressure

Abstract

A spin-triplet superconducting state mediated by ferromagnetic (FM) spin fluctuations has been suggested to occur in the newly discovered heavy-fermion superconductor ${\mathrm{UTe}}_{2}$. However, the recent neutron scattering measurements revealed the presence of antiferromagnetic (AFM) spin fluctuations in ${\mathrm{UTe}}_{2}$. Here, we report the $^{125}\mathrm{Te}$ nuclear magnetic resonance studies of a single-crystal ${\mathrm{UTe}}_{2}$, suggesting the coexistence of FM and AFM spin fluctuations in ${\mathrm{UTe}}_{2}$. 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 interladder 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 ${\mathrm{UTe}}_{2}$.