Daniel Pratt

Unconventional pairing in the iron arsenide superconductors

We use magnetic long-range order as a tool to probe the Cooper-pair wave function in the iron arsenide superconductors. We show theoretically that antiferromagnetism and superconductivity can coexist in these materials only if Cooper pairs form an unconventional, sign-changing state. The observation of coexistence in

Lattice collapse and quenching of magnetism in CaFe[subscript 2]As[subscript 2] under pressure: A single-crystal neutron and x-ray diffraction investigation

\text{Ba}{({\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x})}_{2}{\text{As}}_{2}

Antiretroviral activity of synthetic hypericin and related analogs

then demonstrates unconventional pairing in this material. The detailed agreement between theory and neutron-diffraction experiments, in particular, for the unusual behavior of the magnetic order below

Incommensurate Spin-Density Wave Order in Electron-Doped BaFe2As2 Superconductors

{T}_{c}

Stabilization of an ambient-pressure collapsed tetragonal phase in CaFe[subscript 2]As[subscript 2] and tuning of the orthorhombic-antiferromagnetic transition temperature by over 70 K via control of nanoscale precipitates

, demonstrates the robustness of our conclusions. Our findings strongly suggest that superconductivity is unconventional in all members of the iron arsenide family.

Paramagnetic Spin Correlations in CaFe2As2 Single Crystals

Single-crystal neutron and high-energy x-ray diffraction measurements have identified the phase lines corresponding to transitions among the ambient-pressure paramagnetic tetragonal (T), the antiferromagnetic orthorhombic (O), and the nonmagnetic collapsed tetragonal (cT) phases of

Magnetic ordering and structural distortion in Ru-doped BaFe 2 As 2 single crystals studied by neutron and x-ray diffraction

{\text{CaFe}}_{2}{\text{As}}_{2}

Suppression of antiferromagnetic spin fluctuations in the collapsed phase of CaFe2As2

. We find no evidence of additional structures for pressures of up to 2.5 GPa (at 300 K). Both the T-cT and O-cT transitions exhibit significant hysteresis effects, and we demonstrate that coexistence of the O and cT phases can occur if a nonhydrostatic component of pressure is present. Measurements of the magnetic diffraction peaks show no change in the magnetic structure or ordered moment as a function of pressure in the O phase, and we find no evidence of magnetic ordering in the cT phase. Band-structure calculations show that the transition into the cT phase results in a strong decrease in the iron

Suppression of antiferromagnetic order and orthorhombic distortion in superconducting Ba ( Fe 0.961 Rh 0.039 ) 2 As 2

3d

Effects of Transition Metal Substitutions on the Incommensurability and Spin Fluctuations in BaFe2As2 by Elastic and Inelastic Neutron Scattering

density of states at the Fermi energy, consistent with a loss of the magnetic moment.