Anomalous behavior in a three-dimensional frustrated itinerant electron magnet

We present a simple microscopic theory for the magnetic and electronic properties of a three-dimensional frustrated itinerant electron magnet. Based on the single-band Hubbard model, it is investigated in the weak-correlation limit at a half-filling on the pyrochlore lattice. A doubly-degenerate flat band in the bare spectrum emerges as a character of the fully frustrated geometry. The random-phase-approximation dynamical susceptibility reproduces some characters in the low-frequency regime that were found in the neutron inelastic-scattering experiment of the cubic Laves compound Y(Sc)Mn2, especially in the spectral intensity distribution in the reciprocal space and in the almost irrelevant feature of the distribution to frequency. The quasi-particle selfenergy shows a peculiarity, resulting from an anomalous frequency dependence in the non-interacting dynamical susceptibility, and then it leads to the breakdown of the Fermi-liquid picture.