Haslbeck, F.MLZ* ; Säubert, S.MLZ* ; Seifert, M.MLZ* ; Franz, C.MLZ* ; Schulz, M.MLZ* ; Heinemann, A.MLZ* ; Keller, T.MLZ* ; Das, P. ; Thompson, J. D. ; Bauer, E. D. ; Pfleiderer, C.MLZ* ; Janoschek, M. (Corresponding author)

2018

Abstract: Microscopic coexistence of ferromagnetism and unconventional superconductivity renders UGe$_2$ a candidate for spin-triplet superconductivity. To avoid pair-breaking, spin-triplet superconductivity is mediated by longitudinal spin fluctuations promoted by magnetic Ising anisotropy. Employing the Modulated IntEnsity by Zero Effort (MIEZE) technique - a novel neutron spectroscopy method with ultra-high energy resolution of 1~$\mu$eV - we reveal purely longitudinal spin fluctuations in UGe$_2$ with a dual nature arising from $5f$ electrons that are neither fully itinerant nor localized. 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 this dichotomy may drive spin-triplet superconductivity in UGe$_2$.

Keyword(s): Magnetic Materials (1st) ; Magnetism (2nd)

1. MATSCI
2. ANTARES
3. RESEDA
4. SANS1
5. TRISP

1. ANTARES: Cold neutron radiography and tomography station (SR4a)
2. RESEDA: Resonance spin echo spectrometer (NL5S)
3. SANS-1: Small angle neutron scattering (NL4a)