D.K. Pratt

Anomalous Suppression of the Orthorhombic Lattice Distortion in Superconducting Ba(Fe1-xCox)2As2 Single Crystals

High-resolution x-ray diffraction measurements reveal an unusually strong response of the lattice to superconductivity in Ba(Fe1-xCox)2As2. The orthorhombic distortion of the lattice is suppressed and, for Co doping near x=0.063, the orthorhombic structure evolves smoothly back to a tetragonal structure. We propose that the coupling between orthorhombicity and superconductivity is indirect and arises due to the magnetoelastic coupling, in the form of emergent nematic order, and the strong competition between magnetism and superconductivity.

Coexistence of competing antiferromagnetic and superconducting phases in the underdoped Ba(Fe0.953Co0.047)2As2 compound using x-ray and neutron scattering techniques.

Neutron and x-ray diffraction studies show that the simultaneous first-order transition to an orthorhombic and antiferromagnetic (AFM) ordered state in BaFe2As2 splits into two transitions with Co doping. For Ba(Fe0.953Co0.047)2As2, a tetragonal-orthorhombic transition occurs at TS = 60 K, followed by a second-order transition to AFM order at TN = 47 K. Superconductivity (SC) occurs in the orthorhombic state below TC = 15 K and coexists with AFM. Below TC, the static Fe moment is reduced and a 4 meV spin gap develops indicating competition between coexisting SC and AFM order.

Topological RPdBi half-Heusler semimetals: A new family of noncentrosymmetric magnetic superconductors.

Tunable superconductivity and magnetism in noncentrosymmetric RPdBi provide a new route to exotic topological excitations. We report superconductivity and magnetism in a new family of topological semimetals, the ternary half-Heusler compound RPdBi (R: rare earth). In this series, tuning of the rare earth f-electron component allows for simultaneous control of both lattice density via lanthanide contraction and the strength of magnetic interaction via de Gennes scaling, allowing for a unique tuning of the normal-state band inversion strength, superconducting pairing, and magnetically ordered ground states. Antiferromagnetism with ordering vector (½,½,½) occurs below a Néel temperature that scales with de Gennes factor dG, whereas a superconducting transition is simultaneously supressed with increasing dG. With superconductivity appearing in a system with noncentrosymmetric crystallographic symmetry, the possibility of spin-triplet Cooper pairing with nontrivial topology analogous to that predicted for the normal-state electronic structure provides a unique and rich opportunity to realize both predicted and new exotic excitations in topological materials.

Anisotropic and quasipropagating spin excitations in superconducting Ba(Fe0.926Co0.074)2As2

Inelastic neutron scattering from superconducting (SC) Ba(Fe

Neutron-Scattering Measurements of Spin Excitations in LaFeAsO and Ba(Fe0.953Co0.047)2As2: Evidence for a Sharp Enhancement of Spin Fluctuations by Nematic Order

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Neutron scattering studies of the ferroelectric distortion and spin dynamics in the type-1 multiferroic perovskite Sr 0.56 Ba 0.44 MnO 3

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Competition between stripe and checkerboard magnetic instabilities in Mn-doped BaFe2As2

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Fragile antiferromagnetism in the heavy-fermion compound YbBiPt

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Anisotropic transport and magnetic properties and magnetic-field tuned states of CeZn11single crystals

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Competition and coexistence of antiferromagnetism and superconductivity in underdoped Ba(Fe0.953Co0.047)2As2

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