Incommensurate Spin Fluctuations in the Spin-triplet Superconductor Candidate UTe$_2$

TL;DR

This study reveals that UTe$_2$, a candidate spin-triplet superconductor, exhibits dominant incommensurate antiferromagnetic spin fluctuations without static magnetic order, providing insights into its magnetic properties relevant for topological quantum states.

Contribution

The paper demonstrates that UTe$_2$ has incommensurate spin fluctuations driven by its electronic structure, challenging the assumption of ferromagnetic fluctuations in this material.

Findings

UTe$_2$ shows no static magnetic order down to 0.3 K.

Dominant incommensurate spin fluctuations extend to 2.6 meV.

Electronic structure calculations explain the incommensurate fluctuations.

Abstract

Spin-triplet superconductors are of extensive current interest because they can host topological state and Majorana ferimons important for quantum computation. The uranium based heavyfermion superconductor UTe$_2$ has been argued as a spin-triplet superconductor similar to UGe$_2$, URhGe, and UCoGe, where the superconducting phase is near (or coexists with) a ferromagnetic (FM) instability and spin-triplet electron pairing is driven by FM spin fluctuations. Here we use neutron scattering to show that although UTe$_2$ exhibits no static magnetic order down to 0.3 K, its magnetism is dominated by incommensurate spin fluctuations near antiferromagnetic (AF) ordering wave vector and extends to at least 2.6 meV. We are able to understand the dominant incommensurate spin fluctuations of UTe$_2$ in terms of its electronic structure calculated using a combined density functional and dynamic mean field theory.