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Weyl fermions that emerge at band crossings in momentum space caused by the spin–orbit interaction act as magnetic monopoles of the Berry curvature and contribute to a variety of novel transport phenomena such as anomalous Hall effect and magnetoresistance. However, their roles in other physical properties remain mostly unexplored. Here, we provide evidence by neutron Brillouin scattering that the spin dynamics of the metallic ferromagnet SrRuO3 in the very low energy range of milli-electron volts is closely relevant to Weyl fermions near Fermi energy. Although the observed spin wave dispersion is well described by the quadratic momentum dependence, the temperature dependence of the spin wave gap shows a nonmonotonous behaviour, which can be related to that of the anomalous Hall conductivity. This shows that the spin dynamics directly reflects the crucial role of Weyl fermions in the metallic ferromagnet.

The crystal structure, superconducting properties, and electronic structure of a novel superconducting 122-type antimonide, BaPt 2 Sb 2 , have been investigated by measurements of powder X-ray diffraction patterns, electrical resistivity, ac magnetic susceptibility, specific heat as well as ab-initio calculations. This material crystallizes in a new-type of monoclinic variant of the CaBe 2 Ge 2 -type structure, in which Pt 2 Sb 2 layers consisting of PtSb 4 tetrahedra and Sb 2 Pt 2 layers consisting of SbPt 4 tetrahedra are stacked alternatively and Ba atoms are located between the layers.Measurements of electrical resistivity, ac magnetic susceptibility and specific heat revealed that BaPt 2 Sb 2 is a superconducting material with a T C of 1.8 K. The electronic heat capacity coefficient γ n and Debye temperature θ D were 8.6(2) mJ/mol K 2 and 146(4) K, where the figures in parentheses represent the standard deviation. The upper critical field µ 0 H C2 (0) and the Ginzburg-Landau coherent length ξ(0) were determined to be 0.27 T and 35 nm. Calculations showed that it has two three-dimensional Fermi surfaces (FSs) and two two-dimensional FSs, leading to anisotropic transport properties. The d-states of the Pt atoms in the Pt 2 Sb 2 layers mainly contribute to N(E F ). A comparison between experimental and calculated results indicates that BaPt 2 Sb 2 is a superconducting material with moderate coupling.

The spin dynamics in single crystal, electron-doped Ba͑Fe 1−x Co x ͒ 2 As 2 has been investigated by inelastic neutron scattering over the full range from undoped to the overdoped regime. We observe damped magnetic fluctuations in the normal state of the optimally doped compound ͑x = 0.06͒ that share a remarkable similarity with those in the paramagnetic state of the parent compound ͑x =0͒. In the overdoped superconducting compound ͑x = 0.14͒, magnetic excitations show a gaplike behavior, possibly related to a topological change in the hole Fermi surface ͑Lifshitz transition͒ while the imaginary part of the spin susceptibility Љ prominently resembles that of the overdoped cuprates. For the heavily overdoped, nonsuperconducting compound ͑x = 0.24͒ the magnetic scattering disappears, which could be attributed to the absence of a hole Fermi-surface pocket observed by photoemission.

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Abstract. We have performed magnetic susceptibility and neutron scattering measurements on polycrystalline Ag-In-RE (RE: rare-earth) 1/1 approximants. In the magnetic susceptibility measurements, for most of the RE elements, inverse susceptibility shows linear behaviour in a wide temperature range, confirming well localized isotropic moments for the RE 3+ ions. Exceptionally for the light RE elements, such as Ce and Pr, non-linear behaviour was observed, possibly due to significant crystalline field splitting or valence fluctuation. For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the field-cooled and zero-field-cooled susceptibility at T f = 3.7 K, suggesting a spin-glass-like freezing. On the other hand, neutron scattering measurements detect significant development of short-range antiferromagnetic spin correlations in elastic channel, which accompanied by a broad peak athω = 4 meV in inelastic scattering spectrum. These features have striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the short-range spin freezing behaviour is due to local high symmetry clusters commonly seen in both the systems.

A ternary type-I Si clathrate, K 8 Al x Si 46-x , which is a candidate functional material composed of abundant non-toxic elements, was synthesized and its transport properties were investigated at temperatures ranging from 10 to 320 K. The synthesized compound is confirmed to be the ternary type-I Si clathrate K 8 Al 7 Si 39 with a lattice parameter of a = 10.442 Å using neutron powder diffractometry and inductively coupled plasma optical emission spectrometry. Electrical resistivity and Hall coefficient measurements revealed that K 8 Al 7 Si 39 is a metal with electrons as the dominant carriers at a density of approximately 1×10 27 /m 3 . The value of Seebeck coefficient for K 8 Al 7 Si 39 is negative and its absolute value increases with the temperature. The temperature dependence of the thermal conductivity is similar to that for a crystalline solid. The dimensionless figure of merit is approximately 0.01 at 300 K, which is comparable to that for other ternary Si clathrates.

Angle resolved photoemission spectroscopy of Ba(Fe1−xCox)2As2 (x = 0.06, 0.14, and 0.24) shows that the width of the Fe 3d yz/zx hole band depends on the doping level. In contrast, the Fe 3d x 2 − y 2 and 3z 2 − r 2 bands are rigid and shifted by the Co doping. The Fe 3d yz/zx hole band is flattened at the optimal doping level x = 0.06, indicating that the band renormalization of the Fe 3d yz/zx band correlates with the enhancement of the superconducting transition temperature. The orbital-dependent and doping-dependent band renormalization indicates that the fluctuations responsible for the superconductivity is deeply related to the Fe 3d orbital degeneracy.PACS numbers: