Andrew Boothroyd

Abstract:

We show that resonant scattering signals at the Bragg forbidden positions in YVO3 originate from the anisotropic nature of the atomic scattering factor. The E1-E1 scattering from the electric-quadrupole moment is explained entirely through the crystal structure and does not require sensitivity to 3d orbital order. Simulations of the resonance using the FDMNES code suggest that the Jahn-Teller distortion provides an insignificant contribution to the intensity of the forbidden reflection. Thus we show that resonant x-ray diffraction at the vanadium K -edge in YVO3 is largely insensitive, even indirectly, to 3d orbital order through Jahn-Teller distortions. © 2010 The American Physical Society.

Abstract:

We have used inelastic neutron scattering and muon-spin rotation to compare the low energy magnetic excitations in single crystals of superconducting Fe(1.01)Se(0.50)Te(0.50) and non-superconducting Fe(1.10)Se(0.25)Te(0.75). We confirm the existence of a spin resonance in the superconducting phase of Fe(1.01)Se(0.50)Te(0.50), at an energy of 7 meV and a wavevector of (1/2, 1/2, 0). The non-superconducting sample exhibits two incommensurate magnetic excitations at (1/2, 1/2, 0) ± (0.18, - 0.18, 0) which rise steeply in energy, but no resonance is observed at low energies. A strongly dispersive low energy magnetic excitation is also observed in Fe(1.10)Se(0.25)Te(0.75) close to the commensurate antiferromagnetic ordering wavevector (1/2 - δ, 0, 1/2), where δ≈0.03. The magnetic correlations in both samples are found to be quasi-two-dimensional in character and persist well above the magnetic (Fe(1.10)Se(0.25)Te(0.75)) and superconducting (Fe(1.01)Se(0.50)Te(0.50)) transition temperatures.