Low temperature excitations in CeRu₂Si_2-xGe_x alloys

Alloys in the series CeRu₂Si_2-xGe_x have been studied by inelastic neutron scattering. The high temperature quasielastic response is consistent with a smooth decrease in the 4f-conduction electron hybridisation with increasing x. The linewidths are strongly modulated with wavevector Q, indicating the presence of strong RKKY interactions. The single ion component of the dynamical response shows scaling with x and T in good agreement with standard Kondo theory. In the ordered state, for x ≈ 1, the longitudinal spin fluctuations are characterised by an inelastic peak. The strength of this inelastic response decreases with increasing x, as the exchange field wins over the Kondo screening. The neutron cross-sections are well described by a simple ansatz in which the screened state of the 4f electrons is represented by a pair of singlets separated by an energy of order k_BT_K.