Ubiquitous Spin Freezing in the Superconducting State of UTe2

Abstract

In most superconductors electrons form Cooper pairs in a spin-singlet state mediated by either phonons or by long-range interactions such as spin fluctuations. The superconductor UTe${}_2$ is a rare material wherein electrons are believed to form pairs in a unique spin-triplet state with potential topological properties. While spin-triplet pairing may be mediated by ferromagnetic or antiferromagnetic fluctuations, experimentally, the magnetic properties of UTe${}_2$ are unclear. By way of muon spin rotation/relaxation ($\mu$SR) measurements on independently grown UTe${}_2$ single crystals we demonstrate the existence of magnetic clusters that gradually freeze into a disordered spin frozen state at low temperatures. Our findings suggest that inhomogeneous freezing of magnetic clusters is linked to the ubiquitous residual linear term in the temperature dependence of the specific heat ($C$) and the low-temperature upturn in $C/T$ versus $T$. The omnipresent magnetic inhomogeneity has potential implications for experiments aimed at establishing the intrinsic low-temperature properties of UTe${}_2$.

arXiv comment33 pages, 9 figures

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• A review of UTe${}_2$ at high magnetic fields
• The fate of time-reversal symmetry breaking in UTe2
• Fully gapped pairing state in spin-triplet superconductor UTe${}_2$
• Absence of Spontaneous Magnetic Fields Due to Time-Reversal Symmetry Breaking in Bulk Superconducting UTe2
• DFT+μ: Density Functional Theory for Muon Site Determination
• Microscopic imaging homogeneous and single phase superfluid density in UTe${}_2$
• Spontaneous time-reversal symmetry breaking by disorder in superconductors
• Anisotropic Enhancement of Lower Critical Field in Ultraclean Crystals of Spin-Triplet Superconductor UTe2
• ${\mu }^{+}$ Knight Shift in UTe${}_2$: Evidence for Relocalization in a Kondo Lattice
• Intrinsic low-temperature magnetic properties on the ultra-clean UTe${}_2$ with $T_{\mathrm{c}}$ = 2.1 K revealed by ${}^{125}$Te NMR
• Pair-Kondo effect: a mechanism for time-reversal broken superconductivity in UTe${}_2$
• Dramatic elastic response at the critical end point in UTe${}_2$
• Observation of vortex stripes in UTe${}_2$
• Magnetic edge fields in UTe${}_2$ near zero background fields