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The magnon dispersion in Ca2RuO4 has been determined by inelastic neutron scattering on single crytals containing 1% of Ti. The dispersion is well described by a conventional Heisenberg model suggesting a local moment model with nearest neighbor interaction of J=8 meV. Nearest and next-nearest neighbor interaction as well as interlayer coupling parameters are required to properly describe the entire dispersion. Spin-orbit coupling induces a very large anisotropy gap in the magnetic excitations in apparent contrast with a simple planar magnetic model. Orbital ordering breaking tetragonal symmetry, and strong spin-orbit coupling can thus be identified as important factors in this system. [ABSTRACT FROM AUTHOR]

Spin fluctuations in superconducting BaFe2(As1-xPx (x = 0.34, Tc = 29.5 K) are studied using inelastic neutron scattering. Well-defined commensurate magnetic signals are observed at (π, 0), which is consistent with the nesting vector of the Fermi surface. Antiferromagnetic (AFM) spin fluctuations in the normal state exhibit a three-dimensional character reminiscent of the AFM order in nondoped BaFe2As2. A clear spin gap is observed in the superconducting phase forming a peak whose energy is significantly dispersed along the c axis. The bandwidth of dispersion becomes larger with approaching the AFM ordered phase universally in all superconducting BaFe2As2, indicating that the dispersive feature is attributed to three-dimensional AFM correlations. The results suggest a strong relationship between the magnetism and superconductivity. [ABSTRACT FROM AUTHOR]

Magnetic excitations in Ba(Fe0.94Co0.06)2As2 are studied by polarized inelastic neutron scattering above and below the superconducting transition. In the superconducting state, we find clear evidence for two resonancelike excitations. At a higher energy of about 8 meV, there is an isotropic resonance mode with weak dispersion along the c direction. In addition, we find a lower excitation at 4 meV that appears only in the c-polarized channel and whose intensity strongly varies with the l component of the scattering vector. These resonance excitations behave remarkably similar to the gap modes in the antiferromagnetic phase of the parent compound BaFe2As2. [ABSTRACT FROM AUTHOR]

Magnetic correlations in superconducting LiFeAs were studied by elastic and by inelastic neutron-scattering experiments. There is no indication for static magnetic ordering, but inelastic correlations appear at the incommensurate wave vector (0.5 ± &dgr;, 0.5 ∓ &dgr;, 0) with &dgr; ∼ 0.07 slightly shifted from the commensurate ordering observed in other FeAs-based compounds. The incommensurate magnetic excitations respond to the opening of the superconducting gap by a transfer of spectral weight. [ABSTRACT FROM AUTHOR]

The magnon dispersion of ferromagnetic SrRuO3 was studied by inelastic neutron scattering experiments on single crystals as a function of temperature. Even at low temperature the magnon modes exhibit substantial broadening pointing to strong interaction with charge carriers. We find an anomalous temperature dependence of both the magnon gap and the magnon stiffness, which soften upon cooling in the ferromagnetic phase. Both effects trace the temperature dependence of the anomalous Hall effect and can be attributed to the impact of Weyl points, which results in the same relative renormalization in the spin stiffness and magnon gap. [ABSTRACT FROM AUTHOR]

Triplet pairing in Sr2RuO4 was initially suggested based on the hypothesis of strong ferromagnetic spin fluctuations. Using polarized inelastic neutron scattering, we accurately determine the full spectrum of spin fluctuations in Sr2RuO4. Besides the well-studied incommensurate magnetic fluctuations, we do find a sizable quasiferromagnetic signal, quantitatively consistent with all macroscopic and microscopic probes. We use this result to address the possibility of magnetically driven triplet superconductivity in Sr2RuO4. We conclude that, even though the quasiferromagnetic signal is stronger and sharper than previously anticipated, spin fluctuations alone are not enough to generate a triplet state strengthening the need for additional interactions or an alternative pairing scenario. [ABSTRACT FROM AUTHOR]

Inelastic neutron scattering experiments on Sr2RuO4 determine the spectral weight of the nesting induced magnetic fluctuations across the superconducting transition. There is no observable change at the superconducting transition down to an energy of ~ 0.35 meV, which is well below the 2Δ values reported in several tunneling experiments. At this and higher energies magnetic fluctuations clearly persist in the superconducting state. Only at energies below ~ 0.3 meV can evidence for partial suppression of spectral weight in the superconducting state be observed. This strongly suggests that the one-dimensional bands with the associated nesting fluctuations do not form the active, highly gapped bands in the superconducting pairing in Sr2RuO4. [ABSTRACT FROM AUTHOR]

Topological materials with broken inversion symmetry can give rise to nonreciprocal responses, such as the current rectification controlled by magnetic fields via magnetochiral anisotropy. Bulk nonreciprocal responses usually stem from relativistic corrections and are always very small. Here we report our discovery that ZrTe_{5} crystals in proximity to a topological quantum phase transition present gigantic magnetochiral anisotropy, which is the largest ever observed to date. We argue that a very low carrier density, inhomogeneities, and a torus-shaped Fermi surface induced by breaking of inversion symmetry in a Dirac material are central to explain this extraordinary property.

We study the temporal stability of stripe-type spin order in a layered nickelate with x-ray photon correlation spectroscopy and observe fluctuations on timescales of tens of minutes over a wide temperature range. These fluctuations show an anomalous temperature dependence: they slow down at intermediate temperatures and speed up on both heating and cooling. This behavior appears to be directly connected with spatial correlations: stripes fluctuate slowly when stripe correlation lengths are large and become faster when spatial correlations decrease. A low-temperature decay of nickelate stripe correlations, reminiscent of what occurs in cuprates as a result of a competition between stripes and superconductivity, hence occurs via loss of both spatial and temporal correlations.

The magnon dispersion in Ca_{2}RuO_{4} has been determined by inelastic neutron scattering on single crytals containing 1% of Ti. The dispersion is well described by a conventional Heisenberg model suggesting a local moment model with nearest neighbor interaction of J=8  meV. Nearest and next-nearest neighbor interaction as well as interlayer coupling parameters are required to properly describe the entire dispersion. Spin-orbit coupling induces a very large anisotropy gap in the magnetic excitations in apparent contrast with a simple planar magnetic model. Orbital ordering breaking tetragonal symmetry, and strong spin-orbit coupling can thus be identified as important factors in this system.

Magnetic excitations in Ba(Fe0.94Co0.06)2As2: are studied by polarized inelastic neutron scattering above and below the superconducting transition. In the superconducting state, we find clear evidence for two resonancelike excitations. At a higher energy of about 8 meV, there is an isotropic resonance mode with weak dispersion along the c direction. In addition, we find a lower excitation at 4 meV that appears only in the c-polarized channel and whose intensity strongly varies with the l component of the scattering vector. These resonance excitations behave remarkably similar to the gap modes in the antiferromagnetic phase of the parent compound BaFe2As2.

Spin correlations in La2-xSrxCoO4 (0.3 < or = x < or = 0.6) have been studied by neutron scattering. The commensurate antiferromagnetic order of La2CoO4 persists in a very short range up to a Sr content of x = 0.3, whereas small amounts of Sr suppress commensurate antiferromagnetism in cuprates and in nickelates. La2-xSrxCoO4 with x > 0.3 exhibits incommensurate spin ordering with the modulation closely following the amount of doping. These incommensurate phases strongly resemble the stripe phases observed in cuprates and nickelates, but incommensurate magnetic ordering appears only at larger Sr content in the cobaltates due to a reduced charge mobility.

The magnetic excitations in multiferroic TbMnO3 have been studied by inelastic neutron scattering in the spiral and sinusoidally ordered phases. At the incommensurate magnetic zone center of the spiral phase, we find three low-lying magnons whose character has been fully determined using neutron-polarization analysis. The excitation at the lowest energy is the sliding mode of the spiral, and two modes at 1.1 and 2.5 meV correspond to rotations of the spiral rotation plane. These latter modes are expected to couple to the electric polarization. The 2.5 meV mode is in perfect agreement with recent infrared-spectroscopy data giving strong support to its interpretation as a hybridized phonon-magnon excitation.