Low-energy spin fluctuations of the heavy-Fermion compound CeNi₂Ge₂: origin of non-Fermi liquid behavior

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Neutron scattering shows that non-Fermi-liquid behavior of the heavy-Fermion compound CeNi₂Ge₂ is brought about by development of low-energy spin fluctuations with an energy scale of 0.6 meV. They appear around antiferromagnetic wave vectors (1/2 1/2 0) and (0 0 3/4) at low temperatures, and coexist with high-energy spin fluctuations with an energy scale of 4 meV and a modulation vector (0.23, 0.23, 1/2). The energy dependence of the spin fluctuations is a peculiar character of CeNi₂Ge₂ which differs from typical heavy-Fermion compounds, and suggests importance of low-energy structures of quasiparticle bands.