Soshi Ibuka

Sc2Ru3Si4, monoclinic, C2/c (no. 15), a = 19.0663(5) Å, b = 5.27810(10) Å, c = 13.3458(4) Å, β = 127.7710(10)°, V = 1061.62(5) Å3, Z = 8, Rgt(F) = 0.0209, wRref(F2) = 0.0530, T = 293(2) K.

The High Resolution Chopper Spectrometer (HRC) installed at MLF, J-PARC provides opportunities for dynamical studies of materials over a wide energy-momentum space with high resolution. Three types of inelastic neutron scattering experiments can be performed with the HRC: high-resolution experiments in a conventional energy-momentum space, eV neutron spectroscopy, and neutron Brillouin scattering (NBS). Some results have been obtained using these techniques. The NBS option makes the HRC different from other chopper spectrometers. Coherent excitations in non-single-crystal samples can be observed with NBS. On the HRC, NBS experiments were made feasible by reducing the background noise at low scattering angles, and some results were obtained.

Spin wave dispersion of the metallic antiferromagnet Mn₃Pt was investigated just above the order-order transition temperature by using the inelastic neutron scattering technique. The spin wave dispersion at T = 400 K along [100], [110] and [111] directions was isotropic within the measurement accuracy. The dispersion was described by (ħω)² = c ² q ² + δ² with c = 190 meVÅ and Δ = 3.3 meV. Compared with the previous reports, the result shows that large reduction of the stiffness constant with increasing temperature. This feature is similar to that in FePt₃, and will be an indication of the itinerancy of the magnetic moments.

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 first-order transition at T ₀ = 270 K for the platinum-based SrPt₂Sb₂ superconductor was investigated using x-ray diffraction and magnetic susceptibility measurements. When polycrystalline SrPt₂Sb₂ was cooled down through T ₀, the structure was transformed from monoclinic to a modulated orthorhombic structure, and no magnetic order was formed, which illustrates the possibility of a charge density wave (CDW) transition at T ₀. SrPt₂Sb₂ can thus be a new example to examine the interplay of CDW and superconductivity in addition to SrPt₂As₂, BaPt₂As₂, and LaPt₂Si₂. It is unique that the average structure of the low-temperature phase has higher symmetry than that of the high-temperature phase.