Browsing by Author "Taddei, Keith M."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Local Orthorhombicity in the Magnetic ${C}_{4}$ Phase of the Hole-Doped Iron-Arsenide Superconductor ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Na}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$
    (American Physical Society, 2017) Frandsen, Benjamin A.; Taddei, Keith M.; Yi, Ming; Frano, Alex; Guguchia, Zurab; Yu, Rong; Si, Qimiao; Bugaris, Daniel E.; Stadel, Ryan; Osborn, Raymond; Rosenkranz, Stephan; Chmaissem, Omar; Birgeneau, Robert J.; Rice Center for Quantum Materials
    We report on temperature-dependent pair distribution function measurements of Sr1−xNaxFe2As2, an iron-based superconductor system that contains a magnetic phase with reentrant tetragonal symmetry, known as the magnetic C4 phase. Quantitative refinements indicate that the instantaneous local structure in the C4 phase comprises fluctuating orthorhombic regions with a length scale of ∼2 nm, despite the tetragonal symmetry of the average static structure. Additionally, local orthorhombic fluctuations exist on a similar length scale at temperatures well into the paramagnetic tetragonal phase. These results highlight the exceptionally large nematic susceptibility of iron-based superconductors and have significant implications for the magnetic C4 phase and the neighboring C2 and superconducting phases.
  • Thumbnail Image
    Item
    Spin structure and dynamics of the topological semimetal Co3Sn2-xInxS2
    (Springer Nature, 2022) Neubauer, Kelly J.; Ye, Feng; Shi, Yue; Malinowski, Paul; Gao, Bin; Taddei, Keith M.; Bourges, Philippe; Ivanov, Alexandre; Chu, Jiun-Haw; Dai, Pengcheng
    The anomalous Hall effect (AHE), typically observed in ferromagnetic (FM) metals with broken time-reversal symmetry, depends on electronic and magnetic properties. In Co3Sn2-xInxS2, a giant AHE has been attributed to Berry curvature associated with the FM Weyl semimetal phase, yet recent studies report complicated magnetism. We use neutron scattering to determine the spin dynamics and structures as a function of x and provide a microscopic understanding of the AHE and magnetism interplay. Spin gap and stiffness indicate a contribution from Weyl fermions consistent with the AHE. The magnetic structure evolves from c-axis ferromagnetism at $$x = 0$$to a canted antiferromagnetic (AFM) structure with reduced c-axis moment and in-plane AFM order at $$x = 0.12$$and further reduced c-axis FM moment at $$x = 0.3$$. Since noncollinear spins can induce non-zero Berry curvature in real space acting as a fictitious magnetic field, our results revealed another AHE contribution, establishing the impact of magnetism on transport.
  • Thumbnail Image
    Item
    Widespread orthorhombic fluctuations in the (Sr,Na)Fe2As2 family of superconductors
    (American Physical Society, 2018) Frandsen, Benjamin A.; Taddei, Keith M.; Bugaris, Daniel E.; Stadel, Ryan; Yi, Ming; Acharya, Arani; Osborn, Raymond; Rosenkranz, Stephan; Chmaissem, Omar; Birgeneau, Robert J.
    We report comprehensive pair distribution function measurements of the hole-doped iron-based superconductor system Sr1−xNaxFe2As2. Structural refinements performed as a function of temperature and length scale reveal orthorhombic distortions of the instantaneous local structure across a large region of the phase diagram possessing average tetragonal symmetry, indicative of fluctuating nematicity. These nematic fluctuations are present up to high doping levels (x≳0.48, near optimal superconductivity) and high temperatures (above room temperature for x=0, decreasing to 150 K for x=0.48), with a typical length scale of 1–3 nm. This work highlights the ubiquity of nematic fluctuations in a representative iron-based superconductor and provides important details about the evolution of these fluctuations across the phase diagram.