Exchange-enhanced paramagnetism amid a flat band inYCo₂

Revisiting the large family of cubic AB₂ Laves phase materials where the B sublattice forms a pyrochlore network finds examples of correlated electronic and magnetic phases that are worthy of study via a modern approach in terms of flat bands and topology. YCo₂ is a cubic-Laves phase exchange-enhanced paramagnet sitting close to a ferromagnetic instability. We present ARPES and DFT results that show a flat electronic band lying ≈ 300 meV below E_F, and inelastic neutron scattering (INS) data revealing paramagnons extending past 100 meV which are less damped than for narrow-band Stoner magnets like Pd or Ni₃Ga. In addition, we find a striking zone-to-zone momentum dependence of the paramagnon intensity which appears inconsistent with q-independent Stoner theory. We present our analysis of the paramagnons using a diffusive model for the magnetic susceptibility and discuss our analysis of the Brillouin-zone dependent variation of INS intensity.