Spin fluctuations of the archetypal heavy fermion compound ${\mathrm{C}\mathrm{e}\mathrm{R}\mathrm{u}}_2{\mathrm{S}\mathrm{i}}_2$ have been investigated by neutron scattering in an entire irreducible Brillouin zone. The dynamical susceptibility is remarkably well described by the self-consistent renormalization (SCR) theory of the spin fluctuation in a phenomenological way, proving the effectiveness of the theory. The present analysis using the SCR phenomenology has allowed us to determine 14 exchange constants, which show the long-range nature of the Ruderman-Kittel-Kasuya-Yosida interaction.

• Received 10 October 2003

DOI:https://doi.org/10.1103/PhysRevLett.92.097204