Ultra-High Resolution Neutron Spectroscopy of Low-Energy Spin Dynamics in UGe$_2$

TL;DR

This paper demonstrates the use of the MIEZE neutron spectroscopy technique to achieve ultra-high energy resolution in studying low-energy spin dynamics in the ferromagnetic superconductor UGe$_2$, revealing complex spin fluctuation behaviors.

Contribution

The study introduces MIEZE as a powerful method for high-resolution neutron spectroscopy, capable of disentangling local and itinerant spin fluctuations in quantum materials.

Findings

Identification of purely longitudinal spin fluctuations in UGe$_2$

Observation of local spin fluctuations following 3D Ising universality

Detection of itinerant spin fluctuations at length scales near the superconducting coherence length

Abstract

Studying the prototypical ferromagnetic superconductor UGe$_2$ we demonstrate the potential of the Modulated IntEnsity by Zero Effort (MIEZE) technique---a novel neutron spectroscopy method with ultra-high energy resolution of at least 1~$\mu$eV---for the study of quantum matter. We reveal purely longitudinal spin fluctuations in UGe$_2$ with a dual nature arising from $5f$ electrons that are hybridized with the conduction electrons. Local spin fluctuations are perfectly described by the Ising universality class in three dimensions, whereas itinerant spin fluctuations occur over length scales comparable to the superconducting coherence length, showing that MIEZE is able to spectroscopically disentangle the complex low-energy behavior characteristic of quantum materials.