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

TL;DR

This study uses $^{125}$Te NMR to reveal that UTe$_2$ exhibits coexisting ferromagnetic and antiferromagnetic spin fluctuations, with implications for its spin-triplet superconductivity.

Contribution

It provides evidence of coexistence of FM and AFM spin fluctuations in UTe$_2$, highlighting the role of different Te sites and inter-ladder interactions.

Findings

FM spin fluctuations dominate within ladders

AFM spin fluctuations originate from inter-ladder coupling

FM fluctuations may be key to spin-triplet superconductivity

Abstract

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$_2$.