  A focus of recent experimental and theoretical studies on heavy fermion
systems close to antiferromagnetic (AFM) quantum critical points (QCP) is
directed toward revealing the nature of the fixed point, i.e., whether it is an
itinerant antiferromagnet [spin density wave (SDW)] type or a locally-critical
fixed point. The relevance of the local QCP was proposed to explain the
E/T-scaling with an anomalous exponent observed for the AFM QCP of
CeCu_{5.9}Au_{0.1}. In this work, we have investigated an AFM QCP of another
archetypal heavy fermion system Ce(Ru_{1-x}Rh_x)_2Si_2 with x = 0 and 0.03 (sim
x_c) using single-crystalline neutron scattering. Accurate measurements of the
dynamical susceptibility Im[chi(Q,E)] at the AFM wave vector Q = 0.35 c^* have
shown that Im[chi(Q,E)] is well described by a Lorentzian and its energy width
Gamma(Q), i.e., the inverse correlation time depends on temperature as Gamma(Q)
= c_1 + c_2 T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in low
temperature ranges.This critical exponent 3/2 proves that the QCP is controlled
by the SDW QCP in three space dimensions studied by the renormalization group
and self-consistent renormalization theories.
