Spin-wave polarization in single domain uranium selenide

Spin waves in ferromagnetic USe have been measured by inelastic neutron scattering. Previous measurements on a multidomain USe sample show that the spin wave branch has a zone center frequency of ≊9 THz, and that the spin waves are intrinsically broad. New measurements on a single domain sample show that, in addition, the spin wave is unpolarized. This behavior is unlike that of a classical ferromagnet, in which the polarization is transverse, but similar to behavior observed in some singlet ground state systems.