金属強磁性体SrRuO₃におけるワイルフェルミオン

抄録

Magnetic excitations in a polycrystalline sample of the metallic ferromagnet SrRuO₃ were observed by neutron Brillouin scattering, i.e., inelastic neutron scattering near the forward direction, on the High Resolution Chopper Spectrometer (HRC) installed at MLF J-PARC. While the observed spin wave dispersion is well described by the quadratic momentum dependence, the temperature dependence of the spin wave gap shows a nonmonotonous behavior, which can be related to that of the anomalous Hall conductivity. 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. The present result shows that the fictitious magnetic field produced by the Berry phase is an observable in inelastic neutron scattering and that the spin dynamics directly reflects the crucial role of Weyl fermions in the metallic ferromagnet.